APOGEE and Amateur Spectroscopy

February 17, 2018 / David Whelan / Leave a comment

Drew Chojnowski, APOGEE plate designer and lead of the emission-line stars science group, discusses SDSS and Be stars observed with the APOGEE instrument.

This weekend, APOGEEans David Whelan and Drew Chojnowski attended the Sacramento Mountains Spectroscopy Workshop. The workshop’s goal? To get amateur astronomers interested in pursuing spectroscopy. With a mix of amateurs and professionals in the room, the expertise was readily available, and the excitement was palatable.

On Friday, David Whelan lead a discussion on spectral classification of intermediate- and high-mass stars. This is a science effort that is essential to both APOGEE’s emission-line stars group and high-mass stars studies more generally. Perhaps some knowledgeable amateurs can begin to contribute?

Then on Saturday, Drew introduced the group to observing with the Sloan Telescope. Below, he is shown with one of SDSS’s APOGEE plates.

Drew and an APOGEE plate – teaching people how the SDSS is done.

These kinds of workshops break down the barrier between the amateur and the professional, and opens both groups to new possibilities. With special thanks to the organizers Ken Hudson and Joe Daglen, as well as François Cochard from Shelyak Instruments, we very much look forward to pursuing the science generated by this workshop.

The attendants of the Sacramento Mountains Spectroscopy Workshop. David and Drew are on the far right.

Amateur astronomer Joe Daglen, center, tells workshop attendants about the equipment that he uses to teach undergraduate students about imaging and spectroscopy.

Spotlight on APOGEE: Engineering with Garrett Ebelke

July 5, 2017July 5, 2017 / David Whelan / Leave a comment

Garrett Ebelke (center), with his wife, Stefanie, and their daughter, Madeleine

We have featured the building and delivery of APOGEE-2 several times before (like here, here, and here), so you may recognize the person we are spotlighting today. Garrett grew up in Kansas, but took an early interest in triathlons that brought him to the University of Colorado at Boulder, with all of its lovely mountains, for college. While there, he majored in astronomy. He took a class in observational astronomy that sparked his interest in working with telescopes. So after graduation, when a position as a Telescope Technologist on the 2.5-m SDSS telescope at Apache Point Observatory opened up, he jumped on it…and has been associated with SDSS ever since.

When APOGEE-1 arrived to Apache Point Observatory in 2011, Garrett was working the day shift as a fiber optics technician. His job was to plug plates for each night’s observations. As the telescope shut down for regular summer maintenance, he was asked to support the installation of APOGEE-1. This was the first time that Garrett was exposed to the engineering side of astronomy, and he says that he “was very intrigued”. Below is a picture of Garrett in the clean room with APOGEE-1, along with Principal Investigator Steve Majewski, Instrument Scientist John Wilson, and project scientist Gail Zasowski.

From left to right: Garrett Ebelke, Gail Zasowski, Steve Majewski (reflected), and John Wilson, standing together in the clean room with the APOGEE-1 instrument.

After 18 months at APO, Garrett transitioned to a job as a Telescope Operations Specialist, in which he was up at night running the observations of the SDSS telescope. He used this opportunity to begin taking engineering courses during the daylight hours, so that he could build a better background for instrumentation in astronomy. After several years (and several courses), he was approached about taking place in a unique opportunity: building APOGEE-South. In Garrett’s words: “Since I had seen both the day time plugging and night time operations, I was uniquely qualified to train the Chilean observers/pluggers. Shortly after, I began to design the Plugging and Mapping station with [Chief Engineer] French Leger. As I was handing this design off to French to finalize and fabricate, my wife Stefanie gave birth to our first daughter, Madeleine, and two weeks later, we relocated to Charlottesville, Virginia, so I could become involved in building the APOGEE-South instrument.” Talk about a busy two weeks.

From all accounts Garrett has stayed busy in Virginia ever since. It would take too long to explain everything that he has done to assist with the construction of APOGEE-South; suffice it to say that the end product, safely delivered and installed at Las Campanas Observatory, is a testament to his and many others’ hard work — see the team photo below. He has additionally assisted with upgrades at the University of Virginia’s Fan Mountain Observatory, and is in graduate school at Iowa State University pursuing a Master’s degree in Mechanical Engineering. Garrett says that his graduate coursework has been hugely beneficial to his work with APOGEE, and his impact on the team has been equally so.

The APOGEE team in front of the instrument after it was delivered and installed in the instrument room at Las Campanas Observatory. Kneeling, from left: Garrett Ebelke, John Wilson, Jimmy Davidson. Middle: Matt Hall, Mita Tembe, Fred Hearty, Juan David Trujillo. Back: Nick MacDonald.

¡APOGEE-Sur ha llegado! (APOGEE-South Has Arrived!)

January 30, 2017January 30, 2017 / David Whelan / Leave a comment

Estamos muy contentos de compartir algunas fotos de la llegada e instalación de APOGEE-Sur en el telescopio du Pont del Observatorio de Las Campanas. Para comenzar, una foto de APOGEE-Sur siendo retirado del contenedor—el mismo contenedor en el que fue colocado el mes pasado en los Observatorios Carnegie.

We are very excited to share with you some photos of the safe arrival and installation of APOGEE-South at the du Pont telescope, Las Campanas Observatory. To start, here is a picture of APOGEE-South being removed from its shipping container — the same container that it was placed in at Carnegie Observatories last month.

1.APOGEE-Sur está siendo retirado del contenedor delante del telescopio du Pont del Observatorio de Las Campanas. APOGEE-South is being removed from its shipping container at the du Pont telescope, Las Campanas Observatory.

APOGEE-Sur está siendo retirado del contenedor delante del telescopio du Pont del Observatorio de Las Campanas.
APOGEE-South is being removed from its shipping container at the du Pont telescope, Las Campanas Observatory.

Un gran equipo humano llevó a cabo la instalación. Abajo se puede ver a los miembros del equipo, excepto Sanjay Suchak, que tomó la fotografía. Están en un laboratorio criostático que fue especialmente construido para APOGEE-Sur en el telescopio du Pont.

A large crew assembled for the installation effort. Below you see the team that assembled on the mountain, except for Sanjay Suchak who took the picture. They are standing together in the cryostat lab that was specially built for APOGEE-South at the du Pont telescope.

1.¡El equipo! En la fila de atrás, de izquierda a derecha: Nick MacDonald (University of Washington), Garrett Ebelke (University of Virginia), Matt Hall (UVa), Mita Tembe (UVa), Fred Hearty (Penn State University) y Steven Majewski (UVa). En la fila de enfrente, de izquierda a derecha: John Wilson (UVa), Jimmy Davidson (UVa) y Juan Trujillo (UW). Créditos: Sanjay Suchak The crew! In the back row, from left to right: Nick MacDonald (University of Washington), Garrett Ebelke (University of Virginia), Matt Hall (UVa), Mita Tembe (UVa), Fred Hearty (Penn State University), and Steven Majewski (UVa). In the front row, from left to right: John Wilson (UVa), Jimmy Davidson (UVa), and Juan Trujillo (UW). Photo credit: Sanjay Suchak

¡El equipo! En la fila de atrás, de izquierda a derecha: Nick MacDonald (University of Washington), Garrett Ebelke (University of Virginia), Matt Hall (UVa), Mita Tembe (UVa), Fred Hearty (Penn State University) y Steven Majewski (UVa). En la fila de enfrente, de izquierda a derecha: John Wilson (UVa), Jimmy Davidson (UVa) y Juan Trujillo (UW). Créditos: Sanjay Suchak
The crew! In the back row, from left to right: Nick MacDonald (University of Washington), Garrett Ebelke (University of Virginia), Matt Hall (UVa), Mita Tembe (UVa), Fred Hearty (Penn State University), and Steven Majewski (UVa). In the front row, from left to right: John Wilson (UVa), Jimmy Davidson (UVa), and Juan Trujillo (UW). Photo credit: Sanjay Suchak

Una vez que APOGEE-Sur fue instalado, había que conectar los largos cables de fibra óptica que unen el instrumento con el telescopio. La tarea comenzó con una reunión para discutir la mejor manera de canalizar los cables de fibra óptica.

Once APOGEE-South was in place, its long fiber optic cables had to be fed to the telescope. To begin with, a meeting took place at the APOGEE-South instrument to discuss what needed to be done to ensure that the fiber optics were routed safely.

1.Discutiendo los procedimientos para canalizar los cables de fibra óptica desde el instrumento APOGEE-Sur al telescopio. Discussing the procedure for routing the fiber optic cables from the APOGEE-South instrument to the telescope.

Discutiendo los procedimientos para canalizar los cables de fibra óptica desde el instrumento APOGEE-Sur al telescopio.
Discussing the procedure for routing the fiber optic cables from the APOGEE-South instrument to the telescope.

Después de ultimar los detalles, Fred, Garrett, Nick, Jimmy y Juan desenrollaron los cables de fibra óptica.

After all the details had been ironed out, Fred, Garrett, Nick, Jimmy, and Juan unrolled the fiber train.

1.Fred, Garrett, Nick, Jimmy y Juan trabajan coordinadamente para desenrollar con cuidado los 50 metros de fibra óptica. Fred, Garrett, Nick, Jimmy, and Juan work in concert to carefully unfurl the 50-meter long fiber train.

Fred, Garrett, Nick, Jimmy y Juan trabajan coordinadamente para desenrollar con cuidado los 50 metros de fibra óptica.
Fred, Garrett, Nick, Jimmy, and Juan work in concert to carefully unfurl the 50-meter long fiber train.

Luego, Garrett desde abajo y Mita desde arriba trabajaron con cuidado para conectar la fibra desde el laboratorio criostático a la cúpula.

Then, Garrett from below and Mita from above worked to carefully feed the fiber train from the cryostat lab into the observatory dome.

1.Izquierda: Garrett en el laboratorio criostático pasando los cables de fibra óptica a través de un orificio en el techo. Derecha: Mita está arriba en la sala de observación, tirando cuidadosamente del cable. También en la foto de la derecha, se aprecia el telescopio (amarillo) y el brazo de soporte (estructura azul oscuro a la izquierda), que será descrito más adelante. Left: Garrett is shown in the cryostat lab feeding the fiber train through a hole in the ceiling. Right: Mita is above the same hole, carefully bringing the fiber train into the observatory room. Also in the right-hand picture, notice the telescope (yellow) and the boom arm (dark blue structure on the left), which will be discussed below.

Izquierda: Garrett en el laboratorio criostático pasando los cables de fibra óptica a través de un orificio en el techo. Derecha: Mita está arriba en la sala de observación, tirando cuidadosamente del cable. También en la foto de la derecha, se aprecia el telescopio (amarillo) y el brazo de soporte (estructura azul oscuro a la izquierda), que será descrito más adelante.
Left: Garrett is shown in the cryostat lab feeding the fiber train through a hole in the ceiling. Right: Mita is above the same hole, carefully bringing the fiber train into the observatory room. Also in the right-hand picture, notice the telescope (yellow) and the boom arm (dark blue structure on the left), which will be discussed below.

Abajo en la sala criostática, los manojos de fibras deben ser conectados al criostato donde reside APOGEE-Sur. Como se muestra más abajo, cada manojo de fibras se acopla a un conector.

Down in the cryostat room, the bundles of fibers need to enter the APOGEE-South’s cryostat, or temperature-controlled inner workings. As shown below, this is managed by plugging each fiber bundle into a port.

Manojos de 30 fibras cada uno son conectados al criostato del instrumento APOGEE-Sur.
Bundles of thirty fibers each are ported upon entering the APOGEE-South instrument’s cryostat.

Arriba en la cúpula, el cable que contiene todas las fibras se entrelaza a un largo brazo (la estructura azul en la imagen de abajo) que mantendrá las fibras suspendidas durante el funcionamiento del instrumento.

Up in the observatory dome, the fiber longlink conduit was dressed to a long boom (the blue trusswork in the picture below) that will keep the fibers suspended during operation.

Después de conectar los manojos de fibras al telescopio, John y Nick usan un ordenador para revisar que todas las conexiones se han hecho correctamente. Mientras tanto, Fred, Garrett y Juan unen las fibras al brazo de soporte.
After the fiber bundles were all connected to the telescope, John and Nick used a computer to check that they had each been placed in the correct port. Meanwhile, Fred, Garrett, and Juan attached the fiber train to the boom.

Al final de la operación las fibras conectaban el criostato, a través del techo y a lo largo del brazo de soporte, con el telescopio. Para celebrar el éxito, el equipo se puso sus camisetas de APOGEE.

When all was said and done, the fibers were safely installed, from cryostat, through the ceiling, along the boom, to the telescope! To celebrate, the crew wore matching APOGEE T-shirts.

¡Camisetas a tono! Buen trabajo en la instalación de las fibras.
Matching T-shirts! Job well done on the fiber installation.

A continuación, el sistema óptico debe ser colocado en el criostato. Para hacer ésto, el laboratorio criostático fue transformado en una sala limpia para impedir que el polvo y otras partículas contaminaran el interior del instrumento. Este trabajo se está desarrollando ahora—¡deseemos suerte a nuestro equipo en la siguiente etapa de la instalación del instrumento APOGEE-Sur!

Next, the optics have to be placed in the cryostat. To do this, the cryostat lab is being turned into a clean room to prevent dust and other particulates from polluting the inside of the instrument. This work is ongoing — please wish our crew the best of luck on this next stage of the APOGEE-South instrument installation!

Izquierda: Garrett parece particularmente atractivo en su habitación limpia. Derecha: Matt limpia el exterior del criostato de APOGEE-Sur, preparándolo para abrirlo.
Left: Garrett looks particularly fetching in his clean room get-up. Right: Matt cleans off the outside of the APOGEE-South cryostat, preparing it to be opened.

Special thanks to Andres Meza, Carles Badenes, and Barbara Pichardo for making this dual-language blog post possible.

APOGEE-2S: ¡probado, embalado y enviado! Tested, Packed, and Shipped!

December 20, 2016December 21, 2016 / David Whelan / 1 Comment

The APOGEE-2 instrument team reached a significant milestone this week — the APOGEE-2 South spectrograph has begun its long journey to Chile! It is a clone of the spectrograph that is already operating on the Sloan Telescope, and will soon be operating on Carnegie Observatories’ du Pont telescope at Las Campanas Observatory. Reaching this milestone was no small feat; instrument components needed to be checked and re-checked, the spectrograph had to be meticulously packed, and it had to be transported across North America before being loaded on a ship.

El equipo de instrumentos de APOGEE-2 alcanzó un hito significativo esta semana, ¡el espectrógrafo APOGEE-2 Sur ha comenzado su largo viaje a Chile! Es un clon del espectrógrafo que ya está operando en el telescopio Sloan y pronto funcionará en el telescopio du Pont operado por los Observatorios Carnegie en el Observatorio de Las Campanas. Alcanzar este hito no fue una hazaña menor; las componentes del instrumento necesitaban ser revisadas una y otra vez, el espectrógrafo tenía que ser meticulosamente empaquetado y transportado a través de Norteamérica antes de ser cargado en un barco.

They say a picture is worth a thousand words, but frankly there is no other way but pictures to show how hard the APOGEE hardware team has been working to put all of the pieces together at the University of Virginia.

Dicen que una imagen vale más que mil palabras, pero francamente no hay otra forma que no sea usando imágenes para demostrar lo duro que el equipo de APOGEE ha estado trabajando para juntar todas las piezas en la Universidad de Virginia.

In the left-hand image below is technician Sophia Brunner. She is holding a small mirror, with which she is inspecting what is known as a v-groove block — a component that helps direct the fiber optic cables that pass light from the telescope to the spectrograph itself. On the right you can see a close-up of the v-groove block, with the v-grooves visible above Sophia’s hands. To the left of the v-grooves are channels filled with fiber-optic bundles. When the spectrograph is operational, light from individual stars will be passing through each fiber-optic cable, and so the v-groove block allows the light form each of those stars to be sent separately through the spectrograph and recorded. These fiber optics mean that APOGEE has the capability of simultaneously observing 300 stars!

En la imagen de la izquierda a continuación se encuentra la técnica Sophia Brunner. Ella sostiene un pequeño espejo con el que está inspeccionando lo que se conoce como un bloque de ranura en V, un componente que ayuda a dirigir los cables de fibra óptica por donde pasa la luz desde el telescopio al espectrógrafo. A la derecha se puede ver un primer plano del bloque de ranuras-V, con las ranuras visibles por encima de las manos de Sophia. A la izquierda de las ranuras-V se encuentran canales llenos de haces de fibra óptica. Cuando el espectrógrafo está en funcionamiento, la luz de las estrellas individuales pasará a través de cada cable de fibra óptica, por lo que el bloque de ranura en V permite que la luz de cada una de esas estrellas se envíe por separado a través del espectrógrafo para ser registradas. ¡Estas fibras ópticas significan que APOGEE tiene la capacidad de observar simultáneamente 300 estrellas!

Sophie Brunner is inspecting a v-groove block of the fiber assembly, shown in more detail at right.
Sophie Brunner está inspeccionando un bloque de ranura en V del conjunto de fibras, que se muestra con más detalle a la derecha.

How do you work with fiber optic cables? The following pictures illustrate the care and attention necessary to ensure that they do not break (fiber optics are made from glass). On the left, scientist Nick MacDonald is feeding the fiber optic cables through a feed-through in the wall of the APOGEE-2S instrument. It is sort of like feeding a thread through the eye of a needle, only in this case your “thread” can break if you try to force it. On the right, machinist Charles Lam views the 50-meter long cable conduit before fiber installation. The 300 individual fibers are bundled into ten sets of 30 in so-called long-link assemblies. The instrument-side of each long-link assembly is individually fed into the instrument and terminates at a v-groove block as shown above. After all the long-link assemblies were installed they were put into a single conduit and rolled up on a big spool.

¿Cómo trabajas con cables de fibra óptica? Las siguientes imágenes ilustran el cuidado y la atención que son necesarios para asegurar que no se rompan (las fibras ópticas están hechas de vidrio). A la izquierda, el científico Nick MacDonald está alimentando los cables de fibra óptica a través de un orificio en la pared del instrumento APOGEE-2S. Es como pasar un hilo a través del ojo de una aguja, sólo que en este caso el “hilo” puede romperse si se intenta forzarlo. A la derecha, el maquinista Charles Lam inspecciona los paquetes de cables de 50 metros de largo antes de su instalación. En esta imagen, los 300 cables individuales de fibra óptica se envuelven juntos en pequeños paquetes llamados conjuntos de enlace largo; cada conjunto de enlace largo se alimenta a través de una ranura en V individualmente, como se mostró en la imagen anterior. Después de que Charles terminó de inspeccionar los paquetes, éstos se pusieron en un sólo conducto, que posteriormente se enrolló en un gran carrete.

Nick MacDonald is threading long-link assemblies through the side wall of the spectrograph (left). Charles Lam views the conduit stretched out behind the astronomy building at UVa (right).
Nick MacDonald está enhebrando los ensambles de enlace largo a través de la pared lateral del espectrógrafo (izquierda). Charles Lam inspecciona todos los ensambles de enlace largo totalmente estirados, antes de ser agrupados en un conducto, justo afuera del edificio de astronomía en la Universidad de Virginia (derecha).

Once the fibers were in place, the instrument had to be closed up. To test that the spectrograph was working, a single fiber-optic was connected to APOGEE-2S and pointed at the Sun using a small telescope mount. The picture below of all of those happy scientists is all we need to know that the spectrograph performed to specifications.

Una vez que las fibras estuvieron en su lugar, el instrumento tenía que ser cerrado. Para probar que el espectrógrafo funcionaba, una fibra óptica fue conectada a APOGEE-2S y apuntada al Sol usando un pequeño telescopio. La imagen de abajo de estos científicos felices es todo lo que necesitamos para saber que el espectrógrafo cumplió con las especificaciones.

Professor Mike Skrutskie, along with Jimmy Davidson, Mita Tembe, Matthew Hall, and Garrett Ebelke all give the solar test a thumbs up!
El Profesor Mike Skrutskie, junto con Jimmy Davidson, Mita Tembe, Matthew Hall y Garrett Ebelke dan a la prueba solar un ¡pulgar hacia arriba!

Now it’s time to ship! The cryostat was closed, it was wrapped in a big tarp, loaded onto the delivery truck, and then driven to Pasadena, California.

¡Ahora es hora de enviar! El criostato fue cerrado, envuelto en una lona grande, cargado en el camión de la entrega y después conducido a Pasadena, California.

The APOGEE-2S instrument sits on its load cradle(left), and is carried by forklift onto the moving truck (right). El instrumento APOGEE-2S se encuentra en su cuna de carga (izquierda) y es llevado por una carretilla elevadora al camión de carga (derecha).

The APOGEE-2S instrument and accoutrements are carefully stowed (left) before the truck is closed up and drives off (right).
El instrumento APOGEE-2S y sus accesorios se guardan cuidadosamente (izquierda) antes de que el camión se cierre y comience su viaje (derecha).

Two days later, the truck arrived at the Carnegie Observatories in Pasadena, California. The spectrograph and crates were carefully unloaded and stored, awaiting the ocean shipping container, which arrived in the middle of December.

Dos días después, el camión llegó a los Observatorios Carnegie en Pasadena, California. El espectrógrafo y las cajas fueron cuidadosamente descargadas y almacenadas, esperando el contenedor de transporte marítimo, el cual llegará a mediados de diciembre.

A forklift crew unloads APOGEE-2S at the Carnegie Observatories after a successful cross-country trek. Scientist John Wilson gratefully thanks the driving team, Ludden and Gwen, for safely transporting the spectrograph.
La tripulación del montacargas descarga APOGEE-2S en los observatorios Carnegie después de un exitoso viaje. El científico John Wilson agradece al equipo de conductores, Ludden y Gwen, por transportar con seguridad el espectrógrafo.

Shipping the APOGEE-S spectrograph is a delicate business. The spectrograph has to be securely in place on the load cradle as it was in the truck, and a Shock Logger has to be placed to record any jarring movements during transportation. Below, John Wilson can be seen placing the Shock Logger on the load cradle, before the spectrograph is loaded into the shipping crate.

Transportar el espectrógrafo APOGEE-S es algo delicado. El espectrógrafo debe ser colocado cuidadosamente en su cuna de carga mientras se encuentre en el camión, así mismo se debe instalar un registrador de impactos para monitorear cualquier movimiento brusco que se produzca durante el viaje. Abajo podemos ver a John Wilson, instalando el registrador en la cuna de carga, antes de que el espectrógrafo fuera cargado.

John Wilson is mounting the Shock Logger to the APOGEE-S instrument (left). Then, John helps Greg Ortiz load APOGEE-S onto the Maersk shipping container (right).
John Wilson instala un registrador de impactos al instrumento APOGEE-S (izquierda). Más tarde John ayuda a Greg Ortiz a cargar el instrumento en el contendor (derecha).

Once the instrument is loaded onto its cargo ship in Long Beach, it will take about three weeks before it reaches San Antonio, Chile. Keep your fingers crossed for a successful last leg of the journey for APOGEE-2S!

Una vez que el instrumento suba al carguero en Long Beach, tomará alrededor de tres semanas en llegar a San Antonio, Chile.¡Mantenga sus dedos cruzados para una última etapa exitosa del viaje para APOGEE-2S!

Special thanks to Andres Meza and Mariana Cano Diaz for making this dual-language blog post possible.

SDSS Celebrates Leaders Inducted into the National Academy of Sciences

July 3, 2016July 3, 2016 / David Whelan / Leave a comment

This year, we are pleased that two scientists related to the SDSS collaboration have been recognized for their wide contributions to astronomical research.

Professor Meg Urry, of Yale University, has served on the Advisory Committee for SDSS-III and SDSS-IV. Her research focuses of supermassive black holes, and she is known, among other things, for her work that demonstrates Active Galactic Nuclei are a common phase in galaxy evolution.

Dr. Meg Urry of Yale University

Professor Timothy Heckman, of John Hopkins University, has also served on the Advisory Committee for SDSS, as well as being an Astrophysical Research Consortium Board member from 1995 to 2000. His research touches upon the ways that supermassive black holes effect their host galaxies.

Dr. Timothy Heckman, Johns Hopkins University

Congratulations to both Timothy and Meg on their achievements!

A Fundamental Constant of Nature through the SDSS — Una constante fundamental de la Naturaleza a través del SDSS

February 16, 2016February 16, 2016 / David Whelan / Leave a comment

(The following is a guest post by Franco Albareti, a PhD candidate at Universidad Autónoma de Madrid. It is based on recent work with co-workers Johan Comparat and Francisco Prada, which was published last year in the Monthly Notices of the Royal Astronomical Society.)

The physical models we use to describe the world around us and predict new phenomena have some free parameters or constants. These parameters must be adjusted to what is experimentally observed. Among them, those known as the fundamental constants of Nature play a central role in our theoretical understanding of physics.

Los modelos físicos que usamos para describir el mundo a nuestro alrededor y predecir nuevos fenómenos contienen parámetros o constantes sin determinar. Estos parámetros deben ajustarse según lo que se observa experimentalmente. Entre ellos, aquellos conocidos como las constantes fundamentales de la Naturaleza desempeñan un papel fundamental en nuestra comprensión teórica de la Física.

In particular, the fine-structure constant (informally called “α”) tells us the strength of electromagnetic interactions. These interactions are responsible for most of the natural phenomena around us. The correct understanding and description of how they work is not only one of the major achievement of science, but had a tremendous impact on modern life, for instance in telecommunications. The BOSS cosmological survey, one of the surveys within SDSS, has constrained the time variation of the fine-structure constant or, alternatively, the strength of the electromagnetic interactions over more than half the age of our Universe (7 Gyrs).

En particular, la constante de estructura fina (para los amigos, “α”) nos da información sobre la fuerza de las interacciones electromagnéticas. Estas interacciones son responsables de la mayoría de los fenómenos naturales que nos rodean. El hecho de que seamos capaces de entender y describir correctamente cómo funcionan, no sólo es uno de los grandes hitos de la Ciencia, sino que también ha tenido un impacto radical en nuestra forma de vida, por ejemplo, en las telecomunicaciones. El cartografiado cosmológico BOSS, uno de los cartografiados que forman parte del SDSS, ha restringido la variación temporal de la constante de estructura fina o, en otras palabras, la fuerza de las interacciones electromagnéticas durante un período de tiempo que abarca más de la mitad de la edad del Universo (7 Ga).

Any change in the fine-structure constant value will leave its imprint on the separation between two characteristic spectral lines of oxygen, see figure 1 below. These lines are emitted by quasars (extremely luminous galaxies whose light reaches us from the furthest places in the Universe). Thus, a bigger or smaller separation between those lines means that the electromagnetic interactions were stronger or weaker when the light was emitted.

Cualquier cambio en el valor de la constante de estructura fina afectará la separación entre dos líneas espectrales del Oxígeno (ver figura 1). Estas líneas son emitidas por cuásares (galaxias extremadamente luminosas cuya luz nos llega desde los lugares más recónditos de nuestro Universo). Una separación mayor o menor entre estas líneas espectrales significa que las interacciones electromagnéticas eran más fuertes/débiles cuando la luz fue emitida.

Doubly-ionized oxygen lines [OIII] observed in a BOSS quasar spectrum. Líneas espectrales de Oxígeno doblemente ionizado [OIII] observadas en un espectro de un cuásar tomado por BOSS.

Figure 1. Doubly-ionized oxygen lines [OIII] observed in a BOSS quasar spectrum.
Líneas espectrales de Oxígeno doblemente ionizado [OIII] observadas en un espectro de un cuásar tomado por BOSS.

Members of the SDSS collaboration have concluded that the value of the fine-structure constant has remained the same over the last 7 billions years in 1 part in 50,000 (figure 2). For this, more than 10,000 quasar spectra collected by BOSS were used (figure 3).

Miembros de la Colaboración SDSS han concluido que el valor de la constante de estructura fina no ha variado durante los últimos 7 mil millones de años en más de una parte en 50.000 (figura 2). Para ello. más de 10.000 espectros de cuásares tomados por BOSS han sido analizados (figura 3).

Measurements of the variation of the fine-structure constant (Δα/α) as a function of redshift (left panel) and line intensity (right panel). The grey bands in the left figure indicate regions where the sky contamination is strong and, therefore, it affects the measured value. Medidas de la variación de la constante de estructura fina (Δα/α) en función del corrimiento al rojo (imagen izquierda) y la intensidad de las líneas (imagen derecha). Las bandas grises en la figura de la izquierda indican las regiones donde la emisión del cielo es fuerte y, por tanto, afecta al valor medido.

Figure 2. Measurements of the variation of the fine-structure constant (Δα/α) as a function of redshift (left panel) and line intensity (right panel). The grey bands in the left figure indicate regions where the sky contamination is strong and, therefore, it affects the measured value.
Medidas de la variación de la constante de estructura fina (Δα/α) en función del corrimiento al rojo (imagen izquierda) y la intensidad de las líneas (imagen derecha). Las bandas grises en la figura de la izquierda indican las regiones donde la emisión del cielo es fuerte y, por tanto, afecta al valor medido.

Figure 3. Left panel: Composite image with all the BOSS quasar spectra used in this research (10,363) sorted by redshift (each horizontal line is a quasar spectrum). The displacement of the spectral lines to larger wavelengths (effect known as redshift) is due to the cosmological expansion of the Universe. Right panel: Composite image centered on the Oxygen lines and horizontally displaced to account for the redshift effect.
Imagen izquierda: Conjunto de todos los espectros tomados por BOSS que han sido usados en la investigación (10.363) ordenados según el corrimiento al rojo (cada línea horizontal es un espectro de un cuásar). El desplazamiento de las líneas espectrales hacia longitudes de onda más largas (efecto conocido como corrimiento al rojo) es debido a la expansión cosmológica del Universo. Imagen derecha: Misma imagen anterior centrada en las líneas de Oxígeno y corrigiendo el desplazamiento horizontal para tener en cuenta el corrimiento al rojo.

Animation -> The animation below shows an image of a quasar, its full optical spectrum (bottom left), a zoom in the oxygen lines used for the analysis (bottom right), and the measured value of the variation of the fine-structure constant as a function of redshift (top panel). It only displays 200 objects among the >10,000 quasars used for the research. (It starts slow so you can pay attention to all of the information, but then it goes faster)

Animación -> Esta animación muestra una imagen de un cuásar, junto con su espectro en el óptico (parte inferior izquierda), un zoom en las líneas de Oxígeno usadas para el análisis (parte inferior derecha), y el valor medido de la variación de la constante de estructura fina como función del corrimiento al rojo (parte superior). La animación sólo muestra 200 objetos de entre los >10.000 cuásares usados para la investigación. (Empieza despacio para que uno se pueda fijar en toda la información que se muestra, pero luego empieza a ir más rápido.)

Animation of the measured change in the fine structure constant with cosmic time. You may need to refresh this page to see the animation again.

To reach further in the past, when the Universe was five times younger, a dedicated observational program, APOGEE-Q (APOGEE Quasar Survey), is being developed in order to not only measure a variation on the fine-structure constant, but study supermassive black hole masses and quasar redshifts. This program will use an infrared spectrograph from the APOGEE survey instead of the optical one used by BOSS. This allows us to observe the infrared region of the electromagnetic spectrum, where the oxygen lines emitted by distant quasars are found due to the cosmological expansion of the Universe. It will start to take the first data during 2016.

Para remontarnos todavía más atrás en el tiempo, cuando el Universo era cinco veces más joven, un programa observacional específico, APOGEE-Q: APOGEE Quasar Survey, está siendo desarrollado para, no sólo medir la variación de la constante de estructura fina, sino también para estudiar agujeros negros súper masivos y corrimientos al rojo de cuásares. Este programa usará un espectrógrafo infrarrojo del cartografiado APOGEE en vez del espectrógrafo óptico usado por BOSS. Esto nos permitirá observar la región infrarroja del espectro electromagnético, que es donde se encuentran las líneas del Oxígeno emitidas por cuásares muy lejanos debido a la expansión cosmológica del Universo. El programa empezará a tomar los primeros datos en 2016.

Building the APOGEE-2S Spectrograph: Putting Together All the Little Pieces

December 21, 2015 / David Whelan / 1 Comment

Building a spectrograph is no mean feat — and an instrument like the APOGEE spectrograph, with high expectations of precision to meet its mighty science goals, takes time and effort. Today we want to share with you some of the many highlights of the ongoing, and exciting, work being done to make the APOGEE-2S spectrograph, the “twin” spectrograph that is going to perform survey operations on the du Pont Telescope at Las Campanas Observatory in Chile.

Spectrographs have several key components. The light collected by the telescope from a star is collimated by a great big lens before it strikes the diffraction grating, which splits the light into its constituent colors (it’s a fancy prism). The “split” light then travels through a camera so that it can be refocused onto the infrared array, which records the spectrum of the star.

With that in mind, here’s a picture of a part of the collimator known as the collimator positioning actuator, which is the little piece of metal seen at the center of the test dewar (the large cylinder). Its role is to precisely position the collimator lens, to ensure precise collimation at all times.

Josh Peebles from Johns Hopkins is seen here preparing the collimator positioning actuator for cryogenic testing.

Josh Peebles from Johns Hopkins is seen here preparing the collimator positioning actuator inside of a dewar for cryogenic testing.

Next we have some fancy-looking lenses. Because APOGEE works with infrared wavelengths, the lenses have to be made out of substances that are transparent to infrared light, not visible light. As a result, they are actually opaque at visible wavelengths. In the picture below, the lens appears green to us, but this fused silicon lens would be see-through if we had infrared-sensitive eyes.

This is one of the APOGEE-2S spectrograph's lenses (there are six of them in total) up close. It is made of fused silicon, is opaque to our eyes, but is transparent to infrared light. You can see light reflecting from its surface in this photo

This is one of the APOGEE-2S spectrograph’s lenses (there are six of them in total) up close. It is made of fused silicon, and is transparent to infrared light.

New England Optical Systems installed these lenses into the camera barrels — the black cylinders shown below — which will be attached to form the spectrograph’s camera (see further below).

In November, New England Optical Systems finished installing the lenses into the camera barrel.

As of just a few days ago, the camera is now fully assembled, and is currently undergoing tests to ensure that it is working to specifications.

The spectrograph camera is fully assembled, and undergoing a test called laser unequal path interferometry (LUPI for short).

This little photojournal makes building a multi-million dollar spectrograph look so neat and tidy! One final picture to disillusion you. Below is Matt Hall, one of the technicians at the University of Virginia assisting with the build. In this picture, he is testing springs that are used to hold some of the lenses in place. It sounds strange that springs are part of a lens system; but because the APOGEE-2S spectrograph is going to be cooled cryogenically, the lenses will all shrink a little. These springs apply pressure to the edges of the lenses so that they stay in place when they shrink.

This picture illustrates the secret to building instruments like the APOGEE-2S spectrograph: every big piece, like the collimator or camera, is made up of dozens or even hundreds of small, interconnected and interdependent pieces. And each little piece has to be built and tested to ensure that it does its job properly. So here’s to the people, both in Chile and in the U.S., who are currently dedicating their time and effort to build the best spectrograph possible. We look forward to making good use of it!

Matt Hall (UVa) is seen here testing the spring constants of individual spring plungers. As with every small part of the build, it is dealt with meticulously and thoroughly so that the completed spectrograph works at the highest level possible.

Spotlight on APOGEE: Gail Zasowski and Cosmic Dust

October 13, 2015October 15, 2015 / David Whelan / 2 Comments

Meet Gail Zasowski — postdoctoral research fellow at Johns Hopkins University and one of the people behind creating the APOGEE-2 target sample. She earned her PhD at the University of Virginia in 2012 and was then awarded an NSF fellowship at The Ohio State University. She is now a postdoctoral research fellow at Johns Hopkins University. One of Gail’s research interests is the interstellar medium (ISM), and this blog post will introduce how she has used APOGEE to study dust and molecules in the ISM.

Gail grew up in western New York and in Knoxville, Tennessee. In college, she double majored in physics and Latin. As a PhD candidate at UVa, she studied dusty young protostars, the distribution of dust in the Milky Way Galaxy, and stellar populations in open clusters, that is, determining their ages and distances.

One of her explorations with APOGEE data has been in a unique approach to studying diffuse interstellar bands (DIBs), which are absorption features seen in many optical and near-infrared spectra that are believed to be due to large molecules in the ISM. These features are found in nearly every APOGEE spectrum, because the ISM lies between the Earth and every star that we study. The exact nature of these large molecules has been a question for some decades. In one paper, Gail and her collaborators demonstrated that DIBs trace the known distribution of dust throughout the ISM (check out the cool graphic below, from a press release), and can be used to independently verify the large-scale structure of the Milky Way Galaxy.

Gail successfully mapped the strength of DIB features in APOGEE spectra across the Milky Way Galaxy, and used them to show that DIBs trace the distribution of cosmic dust in between stars, but can also be used to trace large scale structure as well. The high latitude data comes from Ting-Wen Lan at JHU.

Even cooler, Gail also found evidence for circumstellar (that is, surrounding a particular star) DIBs in the dusty protoplanetary nebula MWC 922. This is an exciting result: it shows that the molecules that create DIBs are not merely confined to the ISM, but can be found in dusty environments around stars, too. And this is important because one of the unanswered questions about large molecules in space is how they are formed. Placing them around stars, and perhaps eventually showing that they originate around stars before being put in the ISM, would be a major step forward in cosmic dust studies.

Now Gail wants to apply her knowledge of surveys like APOGEE to create models of galaxies that can be used to understand resolved stellar populations (like the Milky Way’s) and unresolved stellar populations (such as the faint light that can be seen in more distant galaxies). This ties in well with several SDSS surveys, which study individual stars (e.g., APOGEE and SEGUE) and entire distant galaxies (e.g., MaNGA. Such a comparison should shed light on those parts of the Milky Way that are not well understood (such as its location in the Tully-Fisher plane, which can be used to determine a galaxy’s mass), as well as tell us about specific properties concerning other galaxies that show similarity to the Milky Way.

Do you think that all work and no play has made Gail a dull astronomer? Not at all! She was a founding member of the Dark Skies, Bright Kids! program at the University of Virginia, which seeks to provide science education in an informal setting to rural, underserved school children in central Virginia. She runs an annual space camp in Columbus, Ohio, that is aimed at middle school students. She is part of the Committee for the Participation of Women in SDSS, which seeks to promote gender balance and an inclusive environment within the collaboration, whose findings were published recently and can be read about on this blog. She also supports LGBTQ initiatives within her own department at JHU.

Gail’s wide-ranging interests, and those of her colleagues, have made a positive impact on the APOGEE survey — not only is it useful for stellar populations studies (which is what it is designed for), but it can also be used to study cosmic dust!

The Apache Point Observatory Galactic Evolution Experiment (APOGEE)

September 22, 2015 / David Whelan / 2 Comments

The following is a synopsis of the new overview paper describing the APOGEE survey. You can find the full paper here.

The first thing to show you about this paper is its authors list. Check out how many contributors there are to this survey:

This, together with its length (50 pages) and number of figures (38!!) may give you some idea of the huge scope of the project. To help us sift through it, here is the executive summary, from the APOGEE Principal Investigator, Steven Majewski:

“This paper gives a broad overview of the motivations, design and execution of the APOGEE survey — a synopsis of how the survey was structured and why.”

This isn’t just a technical overview of the survey, however. Says Majewski:

“The most fun part of this new overview paper — a part for which the entire APOGEE team can be justly proud — is the summary of what the project managed to accomplish in such a relatively short amount of time.”

Here are some examples of what he means:

13 technical papers on subjects like spectrograph design, target selection, data reduction, stellar parameter determination, and collaborations with other surveys
Uses of time series spectral data for projects as diverse as spectroscopic binary characterization and circumstellar variations around hot stars
Detailed maps of stellar radial velocities and metallicities across the Milky Way

It should be mentioned that APOGEE was made possible by a unique 300-fiber-fed, high resolution spectrograph working in the infrared H-band. Hence, thirteen technical papers, while a seemingly large number, were all necessary because APOGEE truly broke ground in a number of ways, both scientific and technical. The actual construction was accomplished by the APOGEE instrument team led by John Wilson (Instrument Scientist) and Fred Hearty (Project Manager).

The detailed maps mentioned in the last bullet deserve a couple of images — they’re too cool not to show. In Figure 24 from the paper, the velocities of stars relative to the Sun are shown against an artist’s impression of the Milky Way Galaxy. Notice how there are clear areas where stars are approaching us, co-moving with us, and moving away from us:

Figure 25 is a similar plot, but showing instead the chemical composition (metal content with respect to hydrogen) in stars across the same survey area. Check out the clear gradient from low-metallicity stars near the edge of the Milky Way’s disk to high-metallicity stars near the Galactic Center:

The general trends shown here are not new; instead, it is APOGEE’s unprecedented detail that makes it the biggest kid on the Galactic evolution block. To put APOGEE into context for us, here is Ricardo Schiavon, the APOGEE Survey Scientist, to sum it up:

“APOGEE has, for the first time, provided a homogeneous database of high quality, high resolution infrared spectra for 150,000 stars, which together offer a rigorously systematic spectroscopic census of our home galaxy. Because of it’s unique infrared sensitivity and ability to punch through the blankets of obscuring Galactic dust in its most crowded regions, APOGEE is unveiling the chemical and kinematical properties of stars in parts of the Milky Way never before probed in such exquisite detail. It is a groundbreaking experiment.”

To put it more bluntly: no one has ever done an infrared survey of Milky Way stars in this way.

APOGEE-South: Guiding with the du Pont Telescope

September 15, 2015 / David Whelan / Leave a comment

An important aspect of telescope control is to make sure that the telescope is tracking the sky at the right rate. Major motors ensure that this is done approximately, by matching the telescope’s position to the Earth’s rotation. But fine-tuning is usually required, and the practice of making these fine-tuned changes is known as “guiding”.

Recently, the SDSS Engineering Crew at Las Campanas Observatory in Chile made a tremendous step forward by figuring out how to guide with the du Pont telescope. APOGEE-South will rely on guiding in order to stay on target while it is making observations. Here is a picture of the guiding camera on the telescope, along with a number of people who worked to make this happen:

The guiding camera is seen at the bottom of the du Pont Telescope at Las Campanas Observatory in Chile. Fred Hearty (head, bottom left), Paul Harding (left, red jacket), John Wilson (behind Paul), French Leger (behind the guiding camera), Juan Trujillo (to right of guiding camera), and John Parejko (who took the picture) are responsible for the recent progress.

John Parejko also created a 30-second movie showing what guiding data look like. The bright “dots” in the video are stars that are being kept in their place by means of the guiding operations.

How SDSS Uses Light to Study the Most Abundant Element in the Universe

August 31, 2015September 10, 2015 / David Whelan / 1 Comment

When we spread out the light from a source into a rainbow, we can reveal information about its chemical makeup. This is how we understand the spectral signatures that reveal that stars have different temperatures. But to learn about the objects that we study in space, whether they be stars, interstellar gas, or galaxies, we first have to know something about the chemical properties of the elements that make up these objects. And one of these elements is, by far, the most important to study: Hydrogen.

Why is hydrogen the most important element to study in astronomy? Primarily because it is the most abundant. If you count the number of hydrogen atoms in all of space (stars, gas, and galaxies), it can be shown that nine out of ten atoms in space are hydrogen. The second-most abundant is helium, which makes up almost one out of ten atoms in space, and every other element is present in only trace amounts — which is not to say that they are unimportant! But in this post, we are going to focus on the big one.

The Hydrogen atom, consisting of a single proton as the nucleus orbited by a single electron.

Hydrogen is also the simplest element on the Periodic Table, as the above diagram shows — one lone proton being orbited by one electron. And like all elements, hydrogen is able to absorb and emit light of certain wavelengths. If the electron is hanging out in the ground state (the n=1 state), it can absorb photons that will shimmy it to the n=2, n=3, n=4, etc. state (and there are an infinite number of these states). Likewise, if the electron begins in the n=2 state, then the atom can absorb photons of light to push it into the n=3, n=4, n=5, etc. state.

When a hydrogen atom is in one of these “excited” states (i.e., n ≠ 1), it also has the opportunity to emit a photon and travel back down to a lower energy level. The photons absorbed have the same wavelengths as the photons emitted, so that they always appear in the same place in a spectrum. In the following illustration, the first four energy levels of the hydrogen atom are shown. Three commonly-studied transitions between different energy levels are named, along with their absorption/emission wavelengths in units of Ångströms (= 10^-10 m). The colors of the line are the approximate colors that they might appear to your eye — with the exception of the Lyman-α transition, which emits in the ultraviolet and is therefore invisible to the human eye.

An illustration of the four lowest energy levels of the Hydrogen atom, and commonly studied transitions between these energy levels.

When studying spectra from space, it is common to study either absorption spectra (spectra with lines that show that atoms are absorbing photons) or emission spectra (spectra with lines that show that atoms are emitting photons). The absorption process is the most common when studying stellar spectra. And for many stars, it is the hydrogen lines that gives us a first indication about the physical properties of the stars. Here, for instance, is the spectrum of an A-type star, i.e., one with strong Hydrogen absorption features:

Spectrum of an A0 star exhibits strong Hydrogen absorption lines where indicated. Other, smaller absorption lines are due to calcium, magnesium, and sodium absorption. This spectrum is taken from the Science Archive Server — check it out!

Galaxies, which are large conglomerations of stars, can also show hydrogen absorption features. But many galaxies, like spiral galaxies or else irregular galaxies with ongoing star formation, actually produce strong emission features. This is because the hydrogen gas that exists between the stars in these galaxies is heated by the stars, so that individual atoms are excited to higher energy levels. A great example is the spectrum of the irregular galaxy NGC 6052, shown below:

Spectrum of the irregular galaxy NGC 6052, with hydrogen emission lines labeled.

You might have noticed in this galaxy spectrum that these hydrogen emission lines appear to sit on top of what look like hydrogen absorption features. The absorption features, as mentioned above, come from the stars in the galaxy, whereas the emission features come from the gas between the stars.

There is other cool stuff that hydrogen can teach us. One of the coolest is called the Lyman-α Forest, which can be used to tell us how much hydrogen gas exists on large scales between galaxies.

This post is part of the SDSS Celebration of the International Year of Light 2015, in which we aim to post an article a month about how SDSS uses light in our mission to study the Universe.

Spotlight on APOGEE: Jonathan Bird and the Formation of the Milky Way

July 22, 2015July 24, 2015 / David Whelan / Leave a comment

The spotlight this month is on Jonathan Bird, the Vanderbilt Initiative for Data-Intensive Astrophysics Postdoc (VIDA) at Vanderbilt University. He is also the APOGEE-2 Science co-chair, for which he is responsible of “making sure that APOGEE-2 takes full advantage of the truly ground-breaking dataset the survey has produced.”

Jonathan is fascinated by the structure of the Milky Way Galaxy: Why is it shaped this way? What was it like in the past? And what will it be like in the future?

Like many people, Jonathan developed a love for astronomy from an early age. His family home in the Santa Monica mountains offered beautiful views of the night sky.

But growing up, his real passion was basketball. He travelled extensively across the west and southwest for tournaments in high school, and was lucky enough to play college ‘ball when he arrived at Caltech — a team in need of little introduction.

Jonathan’s scientific interests have been widespread. Studying radio waves to investigate what determines the large-scale morphology of galaxies; using Cepheid variable stars to measure distances to galaxies; studying Asymptotic Giant Branch stars in order to understand their contribution to stellar synthesis models, a major component of galaxy models; and studying how a disk galaxy is assembled from smaller galaxies. Do you see a theme? In fact, Jonathan’s major interests can best be described by his PhD thesis title: “The Formation and Evolution of Disk Galaxies.” Jonathan’s goal is nothing less than understanding how the Milky Way came to be, how it evolved, and where it is going from here.

Perhaps that is why Jonathan fits in so well with the APOGEE team.

Let’s show one of Jonathan’s models from his 2013 paper on disk galaxy assembly. In the top left panel is shown the distribution of really old stars (11-12 billion years old) in a typical spiral galaxy. From left to right, and then continuing on the bottom, each panel shows the distribution of stars in a different age group (numbers in the bottom right of each panel show the age in billions of years). Notice that the “spiral” shape that we associate with spiral galaxies is found only among stars that are less than about 2 billion years old. As odd as this may seem, this is exactly what astronomers observe: the older stars are found across a large volume across the bulge and halo; whereas younger stars are predominantly found in the disk, where star formation is ongoing.

How does this model hold up against the huge APOGEE-1 dataset? Pretty well, actually. For Jonathan, this is heartening — we have begun to piece together the massively complex stellar history of the Milky Way Galaxy, and we can do it with state-of-the-art telescopes and computer codes. You can follow more about what Jonathan is doing, along with the rest of the APOGEE-2 team, by following us on social media.

Science Blog from the SDSS

News from the Sloan Digital Sky Surveys

Author: David Whelan