APOGEE

The APOGEE-South First Light Field — APOGEE-2 Sur. Observaciones de Primera Luz

/ Karen Masters / 3 Comments

This post was written by Carlos Roman (Instituto de Astronomía, UNAM, Mexico), with help from Roger Cohen (Universidad de Concepción, Chile) and Guy Stringfellow (University of Colorado). Spanish by Carlos Roman.

La región 30 Doradus en la Nube Grande de Magallanes (NGM) fue seleccionada como objetivo para la placa de primera luz del programa APOGEE-2 Sur en el Observatorio de Las Campanas. Esto se decidió en base a algunos razonamientos importantes:

The 30 Doradus region in the Large Magellanic Cloud (otherwise known as the Tarantula Nebula) was selected as the First Light plate for the APOGEE South Survey at Las Campanas Observatory. Several reasons stand out for this choice:

Las Nubes de Magallanes, tanto la Grande como la Pequeña, son dos de los objetos más representativos de el cielo del hemisferio sur. Estas son dos de entre un grupo muy pequeño de galaxias visibles al ojo humano, sin ayuda de telescopios, y son bien conocidas por los habitantes de las regiones australes de nuestro planeta. Las Nubes de Magallanes son también los miembros más cercanos del llamado Grupo Local de Galaxias de la Vía Láctea, lo cual significa que también contienen a los ambientes extragalácticos más cercanos con los que podemos comparar lo que observamos en nuestra Galaxia. Por esta razón, han sido objeto de númerosos estudios, que incluyen mapas muy completos en muchas longitudes de onda, obtenidos con instrumentos en la Tierra y en el Espacio, y desde los observatorios más importantes, incluyendo el Telescopio VISTA del Observatorio Europeo Austral (European Southern Observatory o ESO por su sigla en inglés), o los telescopios espaciales Spitzer, Herschel y GALEX.

The Large and the Small (LMC, SMC) Magellanic Clouds are among the most representative features of the South Hemisphere sky. They are among the handful of galaxies visible to the unaided human eye and are well known to the public in all Austral regions of the planet. The Magellanic Clouds are also the closest members in the Local Group of the Milky Way, which means they are the closest extragalactic environments to which we can compare our own, and therefore they have been the subject of copious studies, that include comprehensive, multi-wavelength surveys both ground and space-based, with facilities like the ESO-Vista Telescope, the Spitzer, Herschel and GALEX space observatories.

La NGM es particularmente famosa por su actividad de formación de estrellas. A pesar de ser una galaxia de morfología irregular y de tener un tamaño relativamente pequeño, su tasa de formación estelar es extremadamente alta. Los complejos de gas molecular en la NGM contienen algunos de los cuneros estelares más brillantes que hemos podido observar, y esto es porque producen muchas estrellas masivas. De hecho, algunas de las estrellas más masivas que se conocen se formaron en la NGM, y en particular, se están formando y desarrollando en la región 30 Doradus, también conocida como la Nebulosa de la Tarántula, una hermosa región de hidrógeno ionizado (o región HII) parcialmente iluminado por el grupo de la estrella R136 en el cúmulo estelar NGC 2070. Este grupo contiene alrededor de 10 de las estrellas más masivas que se conocen, incluyendo a la estrella R136a1, con una masa que se cree supere 300 veces la del Sol, y que es tan lumuinosa como 9 millones de estrellas tipo solar. R136a1 es la estrella más masiva que conocemos.

The Large Magellanic Cloud is particularly famous for its star formation activity. Despite being an irregular, relatively small galaxy, its star forming rate is extremely high. The molecular gas complexes in the LMC host some of the brightest stellar nurseries we can observe, and this is because they produce large numbers of massive stars. In fact, some of the most massive stars known are born in the LMC and in particular, they are being born in the 30 Doradus region, also known as the Tarantula Nebula, a beautiful ionized Hydrogen (HII) region partly illuminated by the star R136 group in the stellar cluster NGC 2070. This group contains about 10 of the most massive stars known, including the source R136a1, with an estimated mass of over 300 solar masses and a luminosity almost 9 millon times higher than our Sun’s. R136a1 is currently the most massive star known to date.

La NGM fue observada como parte del programa APOGEE-2 Sur. En poco tiempo, el instrumento APOGEE proveerá de espectros infrarrojos de alta resolución de miles de estrellas en ambas Nubes de Magallanes, que proveerán de una base de datos sin precedentes que permitirá la reconstrucción de sus historias de formación estelar y de la evolución de sus poblaciones estelares, permitiendo compararlas con las de nuestra Galaxia.

The LMC will be well covered in the APOGEE-2S survey. APOGEE will provide with infrared, high resolution spectra for thousands of stars in both Magellanic Clouds, which will provide an unprecedented database that will allow the reconstruction of their star formation and chemical evolution histories, allowing us to compare them with those of the Milky Way.

La razón por la que se escogió la región 30 Doradus como el campo de primera luz para el relevamiento APOGEE-2 Sur, es debido a su importancia como objeto astronómico, pero también contó su belleza. En las figuras que incluimos abajo, mostramos algunos mapas en colores falsos de la NGM construidas con datos en varias longitudes de onda, y en donde hemos marcado la posición del campo observado con APOGEE, centrado en una posición muy cercana a 30 Doradus. En la primera imagen se muestra a la NGM en el óptico, donde podemos distinguir la población principal de estrellas en la Nube, así como varias regiones HII que se ven como zonas de nebulosidad. En la segunda imagen, vemos a la NGM como fue observada por el Levantamiento de Legado SAGE, del telescopio espacial infrarrojo Spitzer: este mapa muestra en magnífico detalle el brillo de las regiones gaseosas iluminado por estrellas recientemente formadas a lo largo y ancho de la NGM. El tercer mapa, muestra a la NGM como fue observada por el Telescopio Espacial Herschel en el infrarrojo lejano. Esta vez, el mapa traza a detalle la estructura compleja del medio interestelar en la NGM, conformado por una intrincada red de burbujas y filamentos, moldeados por los vientos de las estrellas masivas y los cúmulos estelares en las que se formaron. Sobre esta imagen, colocamos el campo de APOGEE, y señalamos con puntos pequeños todas las estrellas observadas en la placa de primera luz. Ademas, escogimos cuatro de los espectros observados, que mostramos en la parte de la derecha. Estos espectros pertenecen a cuatro estrellas muy masivas de NGM.

We chose the 30 Doradus region as the First Light plate for the APOGEE2S survey because of its importance as an astrophysical subject but also because of its beauty as illustrated in the following three image, where we have highlighted the field of view of the region we will observe with APOGEE, centered close to 30 Doradus.

DSS optical map of the LMC. We can distinguish the main stellar population of the cloud and several HII regions seen as gaseous bubbles. Image Credit: Carlos Roman, SDSS-IV and DSS.

The LMC as seen by the SAGE Legacy Survey of the galaxy made by the Spitzer Space Telescope: it shows in magnificient detail, the glow from gaseous regions illuminated by recently formed stars across the whole galaxy. Image Credit: Carlos Roman, SDSS-IV and Spitzer.

The same region but as seen with the Herschel Space Telescope in the Far-Infrared, this time tracing the complex structure of the interstellar medium of the LMC, seen as an intricated network of bubbles and filaments excavated by the winds of the massive stars and their clusters. Image Credit: Carlos Roman, SDSS-IV and Herschel.

El la cuarta figura, mostramos un acercamiento al campo de primera luz en 30 Doradus y sus alrededores, donde se señala el campo del espectrógrafo APOGEE desde el telescopio Dupont de 2.5m en su óptica principal en el Observatorio de Las Campanbas. Este campo abarca un área de poco más de 3 grados cuadrados, o 16 veces el área de la Luna llena. Dentro de esta área, se obtuvieron espectros para casi 270 objetivos científicos, que se indican en el mapa con símbolos de distintos colores.

Below we show a close-up of the 30 Doradus region and its surroundings, where we have outlined the field of view of the APOGEE spectrograph from Las Campanas Observatory 2.5m Dupont telescope. This field of view spans over 3 square degrees, 16 times the area of the full Moon. Inside this area, we have obtained spectra for 270 scientific targets, which we have also sketched in the map with different colored symbols.

Plot showing locations of proposed fibers on plate. Image Credit Carlos Roman.

La lista de objetivos propuesta incluyó:

The list of targets include:

26 Estrellas Variables Luminosas Azules (Luminous Blue Variables o LBV por su sigla en inglés) y candidatos a estrellas tipo Wolf-Rayet, incluida R136a1. Estas son fuentes muy masivas, que tienen vidas muy cortas y se formaron muy recientemente (hace unos pocos millones de años), de modo que trazan el episodio más reciente en la historia de evolución química de la NGM, y a la vez proveen información crucial sobre la cinemática y las propiedades de los cúmulos masivos de estrellas en los que se formaron. Estas estrellas muestran la fase evolucionada de estrellas muy masivas, y se sabe que muestran grandes variaciones de brillo debido al hecho de que están expulsando rápidamente sus capas externas por la acción de poderosos vientos estelares. La estrella Eta Carinae en nuestra galaxia la Vía Láctea, es un ejemplo bien conocido de este tipo de estrellas. Las LBV también tienen espectros muy característicos, con líneas que presentan lo que se conoce como perfiles tipo P-Cygni, que parecieran mostrar simultáneamente absorción y emisión. Estas características espectrales indican, precisamente, los procesos físicos relevantes a la acción de los vientos.

a) 26 Luminous Blue Variables and Wolf Rayet star candidates, including R136a1. These are very massive sources, which are very short lived and formed very recently, so they trace the current episode in chemical evolution in the LMC as well as crucial information on the kinematics and properties of the massive clusters in which they form. These stars are the evolved stages of very massive stars and they are known to have large variations in brightness due to the fact that they are expelling their external layers by powerful winds. The Milky Way star Eta Carinae is a well known example of this kind of star. LBV stars also very characteristic spectra, with lines that present what is known as a P-Cygni profile, which appears both as an emission and absorption. These features indicate, precisely, the physical processes relevant to the winds.

55 estrellas masivas (tipos espectrales OB) adicionales en el campo de 30 Doradus y en regiones cercanas de formación estelar masiva. Estos objetos fueron seleccionados a partir de una compilación, basada en fotometría infrarroja del proyecto SAGE (A. Bonanos et al., 2009 AJ, 138, 1003), y de un programa de espectroscopia óptica de las complejos de formación estelar N159/N160, localizados al Sur de 30 Doradus (C. Fariña et al., 2009, AJ, 138, 2).

b) 55 additional massive (OB) star candidates in the 30 Dor and surrounding star forming complexes. These targets were selected from the compilation of A. Bonanos, based on infrared photometry from the Spitzer SAGE Legacy Survey of the LMC (2009 AJ, 138, 1003), and from the optical spectroscopic survey of the N159/N160 star forming complexes -located South of 30 Dor- by C. Fariña (2009 AJ, 138, 2).

42 estrellas Super-gigantes, azules, amarillas y rojas. Estas estrellas son equivalentes a distintos tipos de estrellas enanas como el Sol, pero en estos casos sus clases de luminosidad las clasifican como gigantes y super-gigantes. Las estrellas azules son típicamente decenas o cientos de veces más masivas que nuestro Sol. Las estrellas amarillas son de masas más parecidas a las del Sol, mientras que las rojas son estrellas hechas con apenas una fracción de la masa del Sol.

c) 42 blue, red and yellow Supergiants. These stars are giant and supergiant (known as Class I and II) equivalents of dwarf stars like our Sun. Blue stars are typically tens to hundreds of times more massive than the Sun. Yellow stars are closer in mass to our Sun, and red stars are stars made from only a fraction of a solar mass.

80 estrellas tipo Gigantes Rojas y de Secuencia Principal, que representan la población general de la NGM, seleccionadas a partir de fotometría infrarroja. Estas fuentes proveen de una primera mirada a la cinemática, las abundancias químicas y la distribución de metalicidades en las poblaciones de estrellas de la NGM. Hay una relación importante entre estas poblaciones y las estrellas masivas que se observaron, ya que las primeras muy posiblemente se originaron en agregaciones estelares como las que ahora albergan a las estrellas masivas.

b) 80 red giant and 26 main-sequence stars from the mainstream population of the LMC, selected from near-IR photometry. These sources will provide a first look at the kinematics, the chemical abundances and the metallicity distribution function in the stellar populations of the LMC. There is an important link between these populations and the massive stars we are studying, as the first ones were most likely originated in stellar clusters like those hosting the massive stars.

40 objetos asociados con regiones del medio interestelar, principalmente regiones HII asociadas con cúmulos masivos de estrellas. Estos objetos proveen información importante acerca de las propiedades del medio interestelar (gas y polvo) en la NGM, que pueden ser trazadas por líneas características en los espectros, como las llamadas bandas interestelares difusas, pero también por líneas de absorción producidas por carbón y otros metales presentes en el polvo interestelar. La capacidad del espectrógrafo APOGEE para producir información sobre las velocidades radiales, serán esenciales para saber más sobre la estructura cinemática del medio interestelar en la NGM, y cómo las propiedades del medio se relacionan con los diversos ambientes presentes en esa galaxia.
Se incluyeron, finalmente, 32 posiciones vacías para hacer estimaciones del brillo de fondo en la región.

c) 40 targets associated to local ISM regions, mostly HII regions associated with massive star clusters. These targets will provide important information about the properties of the interstellar medium (gas and dust) in the LMC, which can be traced by specific features in the spectra, like the so-called diffuse interstellar bands, but also by absorption features that are produced by carbon and other metals in the dust. The ability of APOGEE to provide information on the radial velocities of the gas will provide crucial information about the kinematical structure of the gas in the LMC, and how the properties of the interstellar medium relate to the diversity of environments present in the galaxy.

Las observaciones de primera luz se tomaron a principios de este mes. Abajo se muestra una imagen compuesta con datos del observatorio espacial Herschel, las posiciones de las fibras usadas y algunos ejemplos de los datos que se obtuvieron.

The first light data was taken earlier this month. Below we show a composite with the Herschel data, fibres overlaid and some examples of the spectral data that was obtained.

First light data for APOGEE2-S instrument. Spectra are of massive stars in the Tarantula Nebula. Image Credit: Carlos Roman.

Here is a link to the press release about this first light for APOGEE South.

A Snapchat Story about APOGEE

/ Karen Masters / Leave a comment

In this compilation of SnapChat’s, Mita Tembe, from the University of Virginia talks about her work with the APOGEE Instrumentation.

Mita began working on hardware for the APOGEE-2S spectrograph as an undergraduate at the University of Virginia and has been working full time for the project as a Lab Technician/Research Assistant since September 2015.

The video includes a tour of the dome at Las Campanas, a high-level explanation of how the APOGEE instrument works, the installation of two optics, and Mita answering questions some students sent in.

How SDSS Uses Mysterious “Missing Light” to Map the Interstellar Medium

/ SDSS 3 / 1 Comment

This post by Gail Zasowski is part of the SDSS Celebration of the International Year of Light 2015, in which we aim to post an article a month in support of the celebration of light. 

 

It is increasingly rare for modern astronomers to work on “old” puzzles — that is, older than they are, or especially older than their advisors are. The last several decades have seen a huge advancement in our understanding of the Universe — we learned that stars evolve over time in predictable ways, that the Milky Way is one distinct galaxy among many, and that the Universe itself is expanding and even accelerating in size “outwards”. Very often, the questions that astronomers work on now are new questions that arise as other problems are answered, or as we build new telescopes and discover things that we didn’t even know we didn’t know about.

But there is one outstanding puzzle that has famously resisted an answer for nearly a century now. This mystery concerns a peculiar pattern of missing light arising from interstellar material — that is, from the giant clouds of dust and gas that lie in the vast distances between stars. These clouds contain atoms and molecules of all the elements that make up the stars and the planets and us — hydrogen, carbon, oxygen, and so on. They are 10^19 (that’s 10 000 000 000 000 000 000) times less dense than the air we breathe, but they are so huge that they contain enough atoms to add up to nearly 15% of the mass of the Galaxy! (Baryonic mass, of course — dark matter is a different story.) And now the SDSS has made some unique contributions to understanding the mystery in these clouds’ missing light.

Figure 1: The inner part of the Milky Way Galaxy, with numerous stars intermixed with giant clouds of interstellar gas and dust. Image credit: Serge Brunier.

Figure 1: The inner part of the Milky Way Galaxy, with numerous stars intermixed with giant clouds of interstellar gas and dust. Image credit: Serge Brunier.

 

Some of the atoms and molecules in interstellar clouds emit light, like visible light or radio waves, that we can see with telescopes. But others don’t emit much light, and the only way we know they’re there is when they absorb some of the light of stars when the light passes through one of these interstellar clouds. Helpfully, each kind of atom or molecule absorbs only specific wavelengths of light, and we can measure these wavelengths in a laboratory to learn what the pattern is for each element or molecule. So when we look at the spectrum of one of these stars seen through a cloud, and we notice that some of the star’s light is missing, we can use the patterns of absorbed wavelengths to figure out what kind of atoms or molecules are in the cloud. For example, this is how we know that the clouds have elements like calcium and potassium in them1.

Okay, on to SDSS and the mysterious missing light! Way back in the late 1910s, astronomers started noticing some absorption patterns in their spectra that were very puzzling. They didn’t act like the patterns from atoms in the stars themselves, so they had to come from interstellar material. And they appeared in the spectra of stars all over the sky, so the material had to be something that was common. But they couldn’t figure out what the particles were! The patterns didn’t match those of anything we knew existed in interstellar clouds, or even anything we had measured in a laboratory.

Fast-forward nine decades, and the situation has progressed a bit, but not as much as one might expect. We now know of almost 500 separate absorption “features” (that is, wavelengths at which light is being absorbed by something), up from the original 2 discovered in the 1910s (Figure 2). We call all of these features “DIBs”, which stands for “Diffuse Interstellar Bands”2. We have determined that the DIBs are more consistent with being caused by molecules than by single atoms, and many people have theories as to which molecules those are. But it was just this year, in 2015, that scientists were first able to show conclusively that a particular molecule — the fullerene ion C60+ — is responsible for a particular DIB (actually, for four of them). The rest remain up for grabs!

Figure 2: The 400 strongest known DIBs. The y-axis shows the typical fraction of background light absorbed when there is enough interstellar dust to absorb almost 60% of the total visible light.

Figure 2: The 400 strongest known DIBs. The y-axis shows the typical fraction of background light absorbed when there is enough interstellar dust to absorb almost 60% of the total visible light.

So where does SDSS come in? Well, proving that certain molecules produce certain DIBs requires a lot of equipment and a molecular spectroscopy laboratory, and that’s not really something SDSS is set up to do. But there’s another related puzzle — how are the molecules that produce the DIBs (whatever they are) distributed throughout the Milky Way? This is an important question, because the big molecules that are most likely to cause the DIBs are the kinds of molecules that contain a lot of the Galaxy’s carbon, which has an impact on things like the chemistry of newly formed planets. But because DIBs are generally only studied in small samples of stars very close to the Sun3, we didn’t have a good understanding of what the molecules were doing elsewhere in the Galaxy.

One group of SDSSers (led by Ting-Wen Lan, a graduate student at Johns Hopkins) tackled this issue by looking for the DIBs’ absorption signatures in optical SDSS spectra of other galaxies and quasars, seen through the Milky Way’s interstellar material. They had to be careful, because the galaxies’ and quasars’ spectra have absorption lines from their own stars and gas clouds, so identifying the weak features from the foreground Milky Way gas can be tricky. But the SDSS provides the biggest dataset available to look for DIBs: the team had so many spectra from SDSS-I, -II, and -III (almost 500,000 of them) that they could add many spectra together to boost the signal, and then map the DIB absorption strength on the sky (see the left side of Figure 3). Because they detected about 20 DIB features in each signal-boosted spectrum, they could also measure how each DIB behaves a little differently with respect to other interstellar gases, like hydrogen or carbon monoxide (Lan et al. 2015). This tells us that there isn’t one single molecule that can explain all of the DIBs!

However, the SDSS optical dataset doesn’t include any sources in the disk or inner parts of the Milky Way. This is because the interstellar material, which is concentrated in these parts of the Milky Way, is made up of not only gas particles but also dust grains (think of tiny soot particles). These dust grains block starlight, and block it much more than the DIB molecules do, especially at optical wavelengths. (Look back at the picture of the inner Milky Way in Figure 1.) So it is very hard to see any stars, galaxies, or quasars to use as “background” sources in which to look for DIBs.

Figure 3: Left: The strength of DIB absorption seen in optical wavelengths from SDSS background galaxies and quasars (Lan et al. 2015) and in infrared wavelengths with APOGEE (Zasowski et al. 2015). Click HERE for an interactive version of this map! Right: The motion of the APOGEE DIB molecules with respect to the Sun. Image credit: T. W. Lan and G. Zasowski. (HERE=http://www.pha.jhu.edu/~tlan/dibs-map.html)

Figure 3: Left: The strength of DIB absorption seen in optical wavelengths from SDSS background galaxies and quasars (Lan et al. 2015) and in infrared wavelengths with APOGEE (Zasowski et al. 2015). Click HERE for an interactive version of this map! Right: The motion of the APOGEE DIB molecules with respect to the Sun. Image credit: T. W. Lan and G. Zasowski.

And this is where APOGEE steps in. APOGEE is unique in the SDSS set of instruments because it measures light at infrared wavelengths. This kind of light is invisible to the human eye (we can perceive some infrared wavelengths ourselves, though we call it “heat”!), but it is very efficient at passing through some materials, including the interstellar dust that blocks visible light (Figure 4). This means that APOGEE is a great tool for measuring starlight — and the bits of it that get absorbed by the DIBs — very far from the Sun in the disk and bulge, where most of the stars and interstellar material are!

Figure 4: Looking at things with optical and with infrared light can lead to very different results! On top, a plastic bag is opaque to visible light, but it is translucent to infrared light from the man's hand. On the bottom, a similar effect occurs in an interstellar cloud, seen with visible light (left), like our eyes, and infrared light (right), like APOGEE. Image credits: NASA/IPAC and ESO. See more optical/IR comparisons HERE. (HERE=http://coolcosmos.ipac.caltech.edu/cosmic_kids/learn_ir/)

Figure 4: Looking at things with optical and with infrared light can lead to very different results! On top, a plastic bag is opaque to visible light, but it is translucent to infrared light from the man’s hand. On the bottom, a similar effect occurs in an interstellar cloud, seen with visible light (left), like our eyes, and infrared light (right), like APOGEE. Image credits: NASA/IPAC and ESO. See more optical/IR comparisons HERE.

So I (Gail Zasowski, a postdoc at Johns Hopkins) led a second group of SDSSers who focused on a single, particularly strong DIB feature that APOGEE could detect. My team measured this feature in front of about 70,000 stars in the APOGEE dataset (Zasowski et al. 2015a). Because most of these stars lie in the dustiest parts of the Milky Way, we were able to fill in the parts of the DIB absorption map that Ting-Wen’s group couldn’t reach with optical data (left panel of Figure 3). We also found that, unlike many of the DIB features at visible wavelengths, this infrared DIB does not disappear in cold, dense interstellar clouds. This behavior means that the APOGEE DIB can be used to measure the approximate amount of interstellar material between us and a background star, including the amount of interstellar dust that blocks so much of the starlight.

Even more excitingly, my team is able to use the DIB features we detect to measure the speed at which the clouds of DIB molecules are moving with respect to the Sun. We can tell that the molecules are generally rotating with the Galactic disk in the same way that hydrogen and other major interstellar components do (right panel of Figure 3).  Since most DIB studies in the past have looked at stars relatively close to the Sun, this is the first time this dynamical behavior has been observed in any sort of large scale way.

My group even found evidence for DIB molecules flowing in the gas surrounding the beautiful Red Square Nebula (Figure 5). This detection may help us identify likely candidates for the molecule itself (Zasowski et al. 2015b).

Figure 5: The Red Square Nebula. Image Credit: P. Tuthill.

Figure 5: The Red Square Nebula. Image Credit: P. Tuthill.

Over the last hundred years, astronomers have learned that there is a large reservoir of unidentified, complex organic molecules in the interstellar medium, seen only in the mysterious signatures they leave in the light of stars shining through them. The SDSS has given us the ability to use these DIB features — even without knowing exactly what causes them! — to map the distribution and velocities of these molecules in the big spaces between the stars.

 

1 Some elements are also traced through their light emission, instead of light absorption. This has to do with the more complicated physics that happens in clouds with different densities and temperatures. For more information, check out http://www.ipac.caltech.edu/outreach/Edu/Spectra/spec.html, or search for “astronomical spectroscopy” online.

2This term refers to three facts about these features. Many of the features at optical wavelengths appear strongest in “diffuse” interstellar clouds, as opposed to very cold dense clouds with atoms packed more closely together (still very far apart by Earth standards, though). The “interstellar” part distinguishes them from absorption features coming from the atmospheres of stars. “Band” is used to indicate that the majority of the features appear broad in the spectrum of a background star — much broader than the narrow absorption lines coming from the star itself.

3This is because bright stars that are close to the Sun tend to have very few absorption lines coming from their own atmospheres, so it’s much easier to detect interstellar absorption lines.

This post by Gail Zasowski is part of the SDSS Celebration of the International Year of Light 2015, in which we aim to post an article a month in support of the celebration of light. 

Spotlight on APOGEE: Gail Zasowski and Cosmic Dust

/ 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.

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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.

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!

Tweep of the Week: Sarah Jane Schmidt

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In charge of the SDSS Twitter account for this week is Dr. Sarah Jane Schmidt, the Columbus Prize Postdoctoral Fellow in the Department of Astronomy at The Ohio State University

Dr. Sarah Jane Schmidt

Dr. Sarah Jane Schmidt

Dr. Schmidt studies the lowest mass and most numerous types of stars in our Galaxy – the M and L dwarfs. These types of cool stars have strong magnetic fields on their surfaces which results in special kinds of extra light from the stars, including dramatic flare events, which Dr. Schmidt works to observe and understand.

Within the SDSS collaboration, Dr. Schmidt has worked or is working on observing cool stars using spectroscopy from several different surveys:

1. A study of ultracool dwarfs with data from a BOSS (Baryon Oscillation Spectroscopic Survey) ancillary project

2. A TDSS (Time Domain Spectroscopic Survey) project looking at long timescale magnetic field variations on late-M and early-L dwarfs

3. Studying the colors of late-K and early-M dwarfs with measurements of temperature and metallicity from spectroscopic observations taken for the APOGEE survey.

This can all be summarised as spectroscopy of the lowest mass stars there are, and Sarah is most interested in using these to constrain the stars ages and how this relates to their magnetic activity.

We hope you’ll join the conversation with Sarah and other SDSS scientists on twitter this week so we can all learn more about the magnetic fields of the smallest stars in the Universe.

How SDSS Uses Light to Understand Stars Inside and Out in the Kepler Field

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Stars are not only fascinating objects in their own right — they also help us understand the history of our Milky Way galaxy. Our galaxy was created as dark matter’s pull brought gas together, and the gas formed stars and planets. As part of the APOGEE survey, we wish to map the Milky Way’s star formation throughout cosmic time. As stars died, many of the elements they fused in their interiors during their lives or death throes are mixed back into the remaining gas, changing its composition and the composition of subsequent generations of stars and providing the raw materials for planets (and humans!) and we are exploring this chemical history as well.

A small part of the spectra of a few of the stars observed by APOGEE. The dark lines are caused by absorption of atoms in the star's atmosphere (or sometimes the Earth's). A few of them are highlighted. The bright lines are caused by emission in the Earth's atmosphere ("night sky lines") These particular stars have also been observed by the Kepler satellite.

A small part of the spectra of a few of the stars observed by APOGEE. The dark lines are caused by absorption of atoms in the star’s atmosphere (or sometimes the Earth’s). A few of them are highlighted. The bright lines are caused by emission in the Earth’s atmosphere (“night sky lines”) These particular stars have also been observed by the Kepler satellite.

APOGEE studies stars by passing their infrared light through gratings that spread the light out in wavelength (think infrared rainbows). We do this for > 250 stars at once (one of the reasons why the APOGEE instrument is fantastic). We can tell a lot about stars from studying these spectra. For example, in an earlier blog post, we discussed how we can tell the surface temperature of stars from such data. Another very important property is the composition of the star, for example, how many atoms of iron, calcium, or oxygen it has relative to hydrogen. The image to the left shows a small part of the spectra we gathered for stars that were also observed by the Kepler satellite. The stars do not give off the same amount of light at each wavelength (=color) of light. Instead, there are many dark lines, which are created when atoms in a star’s atmosphere absorb light at very particular wavelengths. Each element has a different pattern of these absorption lines, and by measuring the depth of these lines (+ additional information and math), we can determine the composition of the gas out of which the star formed.

But this doesn’t tell us everything about the star! In particular, we can’t see inside the star where the original composition of the gas is being transformed from hydrogen into helium as the star ages. We have a good idea of how long it takes for a star with a certain mass and original chemical composition to run out of fuse-able hydrogen in its center (about 10 billion years in the case of a star with the mass and composition of the Sun). When that happens, the star undergoes a dramatic change, turning into a red giant or supergiant. So if we can determine the mass to go with the spectral  composition information for red giants that we observe, we can determine the age of those particular stars.

Measuring the mass of a star is hard work, but one possible technique is to use asteroseismology, which is the study of the waves that move through stars. In the outer parts of stars, these waves are actually sound waves that can evocatively be described as ringing the star like a bell (For more information see The Song of the Stars). The motions of these waves cause a star’s brightness to change by small amounts, and thus the frequency of these waves can be measured by studying the lightcurves of red giant stars. The Kepler satellite, in addition to studying many Sun-like stars looking for transiting planets, also measured the brightnesses over many years of thousands of red giants. The favorite frequencies of waves in different stars have been measured by members of the Kepler Asteroseismic Science Consortium. While much can be learned about the insides of stars from these data, we are particularly intrigued by the fact that how long and at what speed waves can move through the star depends on the star’s density and therefore (with some more math) its mass!

Combining together spectra from APOGEE and lightcurves from Kepler therefore gives us a way to figure out the ages of red giant stars in our Galaxy by measuring the masses and composition of stars that have just exhausted their hydrogen. In conclusion, songs and rainbows are good things.

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. 

APOGEE’s Infrared View of the Stellar Temperature Sequence

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APOGEE surveyed 156,481 stars in its first three years. And of course APOGEE-2 is going to increase this sample size significantly. But to celebrate the successful end of APOGEE and the Data Releases 11 & 12 (also see here), we’d like to share with you a slice of the kind of data it collected.

Some background: The APOGEE/APOGEE-2 instrument collects near-infrared spectra of distant stars, and the survey is aimed at studying the history of the Milky Way Galaxy. How it does that is explained here. Along the way, it has taken spectra of each known spectral type: from hot O-type stars (with surface temperatures of about 30,000 degrees, or five times the surface of our own Sun) down to M-type stars (about 3,500 degrees, or roughly half the temperature of the Sun). Each of the spectral types (O, B, A, F, G, K, M) is defined based on how many and what kind of atomic or molecular species are seen in their spectrum. For instance, O-type stars have lots of singly-ionized atomic species visible in their spectra, whereas A-type stars have very strong hydrogen lines, and M-type stars have lots of neutral molecules, especially lines of TiO when you look in the visible portion of the spectrum.

These spectral types were defined using the visible portion of the spectrum. So when we look in the near-infrared, do they appear to be different? Here we go:

apogee_tempsequence_new2

The O-type star spectrum looks pretty bland — the strongest lines due to ionized Helium in the near-infrared H-band are at 15721 and 16922 Angstroms (the line at 15271 Angstroms is due to interstellar molecules, and is therefore not from the star). The B-type star shows pretty significant absorption lines due to the Brackett series of atomic Hydrogen (those transitions beginning at the n=4 excited state), and those plus a whole bunch of smaller wiggles from other atoms can clearly be seen in the A- and G-type spectra as well. Below that and things look a lot more complicated. If you have experience with data like these, you might be tempted to think that the spectra of the G-, K-, and M-type stars are “noisy”, meaning that they weren’t observed for long enough and therefore weren’t detected well. But that’s not the case: every single spike visible in these spectra is due to an atomic or molecular transition that originates in the photosphere of the star!

All told, these spectra allow us to study sixteen different atomic elements besides hydrogen. Which ones, you ask? Oh all right, I’ll tell you: C, N, O, Na, Mg, Al, Si, S, K, Ca, Ti, V, Cr, Mn, Fe, Co, and Ni. As you can see, this is a truly beautiful, complex dataset. We’ll keep up-to-date science results at this page.

Miembros del SDSS Chileno Visitan APO – Chilean SDSS Members Visit APO

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A post by Garrett Ebelke, Telescope Operation Specialist and APOGEE Hardware Development and Training Coordinator at Apache Point Observatory. Translated into Spanish by Loreto Barcos and Guillermo Damke (University of Virginia), with help from Veronica Motta (Universidad de Valparaíso, Chile).

Publicado por Garret Ebelke, Especialista de Operaciones del Telescopio y Coordinador de Desarrollo y Entrenamiento del Instrumento de APOGEE del Observatorio Apache Point. Traducido al Español por Loreto Barcos-Muñoz y Guillermo Damke (Universidad de Virginia, con ayuda de Veronica Motta (Universidad de Valparaíso, Chile).

Durante la segunda mitad de Abril, los ingenieros Daniel Garrido y Mario Cáceres viajaron desde Chile al Observatorio Apache Point (APO, por sus siglas en inglés), en Nuevo México, como parte del proyecto QUIMAL de la Universidad de La Serena. El objetivo de su viaje fue conocer en profundidad la infraestructura del instrumento de APOGEE para adquirir un conocimiento más acabado de sus numerosos subsistemas. Estos serán replicados en el proyecto APOGEE-2 e instalados en el telescopio du Pont de 2.5 m ubicado en el Observatorio Las Campanas (LCO, por sus siglas en inglés).

During the second half of April, Daniel Garrido and Mario Caceres, both engineers from Chile, travelled to Apache Point Observatory in New Mexico as part of the QUIMAL project at the Universidad de La Serena. The purpose of their trip was to delve deep into the APOGEE infrastructure hardware to gain a better understanding of the numerous hardware sub-systems. These systems will be replicated for the APOGEE-2 project and installed at the du Pont 100-inch Telescope at Las Campanas Observatory.

[For more on the plans for APOGEE observing at Las Campanas see this blog post.]

 

Daniel Garrido (left), Mario Caceres (right) at APO

Daniel Garrido (left), Mario Caceres (right) at APO. Daniel Garrido (a la izquierda) y Mario Cáceres (a la derecha) en APO.

While at APO, they were introduced to the daily task of plugging fiber optics into spectrographic plug plates, all contained within cartridges. They became very familiar with mounting these cartridges to the telescope, and how much care must be taken when handling the cartridges. A similar cartridge design will be used at LCO and Daniel will be heavily involved in assembling and populating the cartridges with fiber optics. Daniel was very eager to explore the internal configuration of the cartridges and quickly got his hands dirty once we opened a cartridge.

Durante su visita a APO, se les inició en la tarea diaria de conectar fibras ópticas a placas espectrográficas, cada una contenida en distintos cartuchos. Daniel y Mario también aprendieron a montar estos cartuchos en el telescopio y entendieron la delicadeza de este proceso. Los cartuchos que se utilizarán en el LCO tendrán un diseño similar. Daniel además estará involucrado en el montaje e instalación de las fibras ópticas en los cartuchos en el LCO. Daniel mostró mucho entusiasmo en explorar la configuración interna de los cartuchos y no tuvo inconvenientes en “ensuciarse las manos” para estudiarlos por sí mismo.

Mario and Daniel plugging fiber optics into a spectrograph plug plate

Mario y Daniel conectando las fibras ópticas en una placa espectrográfica. Mario and Daniel plugging fiber optics into a spectrograph plug plate.

Daniel pushes a cartridge to the telescope

Daniel pushes a cartridge to the telescope. Daniel empuja un cartucho hacia el telescopio.

Daniel (left), Mario (right) explore the internal configuration of an APOGEE fiber optic cartridge

Daniel (a la izquierda) y Mario (a la derecha) exploran la configuración interna de un cartucho de APOGEE. Daniel (left), Mario (right) explore the internal configuration of an APOGEE fiber optic cartridge.

No pudimos dejarlos marcharse de APO sin antes llevarlos a disfrutar del lado oscuro de las operaciones, donde pasaron varias noches familiarizándose con las operaciones nocturnas. Una parte importante de las observaciones es el aprendizaje del software usado para controlar el telescopio y el instrumento de APOGEE.

We couldn’t let them leave APO without letting them join the dark side of operations, where they spent several nights being introduced to nightly operations. A major part of observing is learning the software used to interface with the telescope and the APOGEE instrument.

Moses Marchante (SDSS Telescope Operations Specialist) introduces Daniel and Mario to the interface software used to control the telescope and the APOGEE instrument.

Moses Marchante (SDSS Telescope Operations Specialist) introduces Daniel and Mario to the interface software used to control the telescope and the APOGEE instrument. Moses Marchante, Especialista de Operaciones del Telescopio Sloan Digital Sky Survey (Relevamiento Digital del Cielo Sloan, SDSS por sus siglas en inglés), les enseña a Daniel y Mario el software de la interface usada para controlar el telescopio y el instrumento APOGEE.

This was an excellent start to incorporating some Chilean participants to the APOGEE-2 project, the hardware designs, operational processes and forge an excellent working relationship that will last throughout the entire project.

Esta fue una gran oportunidad para comenzar a incorporar participantes chilenos al proyecto APOGEE-2, al diseño del instrumento, los procesos operacionales, y para forjar una excelente relación de trabajo que durará a lo largo de todo el proyecto.

Daniel and Mario in front of the APOGEE instrument

Daniel y Mario frente al instrumento APOGEE. Daniel and Mario in front of the APOGEE instrument.

All photos were taken using Daniel Garrido’s camera. 

APOGEE2 Engineering Run at Las Campanas Observatory, Chile

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The APOGEE-2 survey of SDSS-IV plans to run observations both at the Sloan 2.5m telescope at Apache Point Observatory, New Mexico, and at the du Pont 2.5m telescope at Las Campanas Observatory in Chile. This will enable observations from both hemispheres, allowing APOGEE-2 to efficiently obtain spectra of stars from all regions of our own Galaxy. Observations from Chile are due to start in 2016.

Last month, several members of the APOGEE-2 Team had three engineering nights kindly provided by the Carnegie Institution on the du Pont 100-inch Telescope. This time was needed for engineering work in preparation for use of the telescope with APOGEE. Paul Harding (Case Western), John Wilson (UVa), French Leger (UW), Garrett Ebelke (APO) and Fred Hearty (PSU) made nighttime measurements in the visual and near-infrared wavelengths to help determine the optimal focal plane location and radius of curvature for wide-field telescope use (ie. the best places to put the tips of the APOGEE fibers so they capture as much of the light from target stars as possible).

du Pont 2.5m

The 3-segment wide-field baffle system on the du Pont 2.5m telescope

Before the run the Las Campanas Observatory staff installed the 3-segment wide-field baffle system so the team could measure vignetting as a function of field location using both traditional and pinhole imaging. The 3-segment wide-field baffle system uses three different blackened, conical, tubes mounted between the telescope mirrors to ensure that only light from the direction the telescope is aimed reaches the focal plane. This was the first time the 3-segment baffle system had been installed in about 15 years.

French Leger

French Leger and the mechanical assembly he designed which allowed precise camera positioning in three dimensions at various locations behind the telescope.

 

Installation of the assembly

Installation of the assembly. In the foreground are Paul Harding (left) and Oscar Duhalde (right, a member of the Observatory Staff).

This run was an excellent first start to learning the wide-field capabilities of the du Pont telescope and how best to position the hundreds of fibers in the focal plane.  Another run is planned for late this year to make further measurements.