The Open Cluster Chemical Abundance and Mapping Survey

Guest post by John Donor.

Astronomers have always been fond of the Milky Way, after all, it is our home. But it’s more than just our home, it’s also our most important laboratory for studying galaxy evolution. We can study the Milky Way in tremendous detail, compared to any other galaxy. So what does our host galaxy tell us about galaxy evolution?

Let’s start at the very beginning (as Julie Andrews said, “a very good place to start”). I literally mean the very beginning: the Big Bang. While the “bang” itself was perhaps the most exciting event in cosmic history, the aftermath of the Big Bang was really rather dull. After the Universe calmed down a bit, all of existence was just endless clouds of gas; Hydrogen and Helium gas to be precise. No stars. No galaxies. Certainly no planets or life.

But fortunately this boring state of affairs quickly corrected itself. As gravity took over, gas began to collect into what would become galaxies. As the gas collected, it slowly became dense enough to form the first stars. Stars are very exciting. In their hot, dense cores, they fuse Hydrogen and Helium into the heavier elements (Carbon, Oxygen, Iron, etc.) that we’re all more familiar with. And when they die, they often die spectacularly in supernovae.

Star deaths are particularly important to our story because that’s how heavier elements (everything besides Hydrogen and Helium) are released into a galaxy. But death is not the end! There’s still plenty of gas in a galaxy, so it forms more stars, now with a slightly higher concentration of heavier elements in them from the previous generation of stars. This is the life-cycle of a galaxy: make stars, become enriched by dying stars, make more stars, repeat. Galaxies aren’t homogenous blobs though: they have interesting structure such as spiral arms and central bulges. Due to the effects of gravity, their mass tends to be more concentrated at their centers. More mass means more stars. More stars means more heavy elements enriching the gas in that part of the galaxy.

A simple illustration of the build up of heavier elements in a galaxy (credit: ESA/Hubble & NASA).

This very simple model already points us towards a key piece of observational evidence in studying galaxy evolution: chemical enrichment. Or more specifically, the rate at which that chemical enrichment changes as we move through the galaxy. To measure chemical enrichment, astronomers often simply measure Iron (Fe) and Hydrogen (H). The ratio of Iron to Hydrogen (Fe/H) gives an exact numerical representation of the level of chemical enrichment, often called “metallicity”. The exact rate at which Fe/H changes with respect to the distance from the center of the galaxy, or the Galactic metallicity gradient, has been the topic of numerous studies dating as far back as 1979.

The Apache Point Observatory Galactic Evolution Experiment (APOGEE) has made measurements of the chemical enrichment (Fe/H) of over 200,000 stars to date. But this is only half the battle. To measure the Galactic metallicity gradient, distances from the center of the Galaxy are needed as well. This might seem easy: measuring distance from the Galactic center is a simple geometry problem, if you know exactly where the object you’re measuring is. Unfortunately, finding the distance to celestial objects can be difficult.
There are a variety of methods for finding astronomical distances, but almost all of them focus on finding the actual intrinsic brightness of an object. Since brightness decreases predictably as we move farther from an object, a change in brightness (intrinsic – observed) must correspond to a certain distance. Of course the observed brightness is very easy to measure! Finding the intrinsic brightness is the focus of entire sub-fields in astronomy.

The perfect measuring stick for studying the galactic abundance gradient will then have both (relatively) easily measured chemistry and a measured reliable distance. Among the best objects fitting this description are open star clusters. Open clusters are large groups of gravitationally bound stars (meaning they’re very close together) that formed at the same time, from the same material. Remember when we discussed stars forming out of gas? Most of these gas clouds are massive (millions of times the mass of our Sun), and thus can produce tens or even hundreds of thousands of stars. The resulting stars tend to remain gravitationally bound in an open cluster.

The open cluster M67, with all the stars observed by APOGEE boxed. (Credit: SDSS)

Open clusters have a number of useful properties. Since all of the stars formed from the same cloud, they all have approximately the same chemical makeup. They are also all approximately the same age (give or take a few million years, but that’s a cosmic eye-blink). These two properties make open clusters particularly easy to model. The models predict both intrinsic and easily observable properties of the cluster (e.g. observed brightness and color patterns), so to determine the intrinsic properties of an open cluster, we only need to find a model that matches it well. With an intrinsic brightness, we can quickly calculate the distance to an open cluster.

APOGEE has observed stars in the fields of hundreds of open clusters (e.g., M67 seen here with observed APOGEE stars marked). But simply being in the same area as an open cluster doesn’t mean the star is part of the gravitationally bound group of stars. It’s an age-old problem for astronomers: we only see a 2D map of the 3D sky. A star in the field of an open cluster could easily be hundreds of light years in front of or behind the gravitationally bound group of stars. The Open Cluster Chemical Abundances and Mapping (OCCAM) survey considers all the APOGEE stars falling in open cluster fields. Determining whether or not a star is in fact a member of the gravitationally bound group can be difficult.

The OCCAM survey relies on the fact that cluster member stars are gravitationally bound. Gravitationally bound stars move through the galaxy together and thus will have similar velocities when measured from Earth. The OCCAM survey combines line-of-sight velocity measurements (Doppler Velocity) from APOGEE with measurements of velocity perpendicular to the line of site (proper motion) from the recent Gaia Data Release 2 to isolate cluster members from non-members.

With uniform APOGEE chemical measurements from member stars in many open clusters, and distance measurements obtained from modeling the open clusters, we can finally measure a high precision Galactic abundance gradient that will be used to calibrate models of galaxy evolution. And that’s one more piece in the puzzle of how our own Milky Way formed and evolved.

SDSS-V Is Underway!

“Everything in this project makes life challenging.”

“Sure, but challenges make life interesting!”

This conversation occurred at a very special SDSS meeting in the middle of last month, and indeed no one could accuse SDSSers of ever taking it easy.  More than two years before the end of SDSS-IV, plans are well underway for its successor, SDSS-V.  Last month’s meeting was the first in-person gathering of the current major players since the Sloan Foundation awarded a $16M grant to the survey.  However, members of the team have been working hard for three years already: identifying the most exciting science goals, simulating survey strategies, and designing new hardware, among other tasks.  Dr. Juna Kollmeier, from The Carnegie Observatories, was selected as SDSS-V Director last spring, and other members of the Management Committee were chosen shortly afterwards. The core projects are now solidifying and the hardware is being prototyped. It’s an exciting (and oh so busy) time!

The science and hardware teams listen to Director Kollmeier open the meeting, in the historic library at the Carnegie Observatories in Pasadena, USA.

The team published a description of the project last fall for the astronomical community, which you can find here. In summary, SDSS-V will consist of three “Mappers,” much like how SDSS-IV now consists of eBOSS, MaNGA, and APOGEE-2.

The Milky Way Mapper will observe millions of stars in our Milky Way Galaxy and in its companion Magellanic Clouds, tabulating their motions and their compositions to study how stars form, disperse throughout space, make heavy elements, and die.  The team will also look for the signatures of planets and invisible companions (including black holes) around the stars.  The Local Volume Mapper will measure the strength of light emitted from interstellar gas in the Milky Way, the Magellanic Clouds, the Andromeda Galaxy, and other nearby galaxies.  This emission tells us about how the gas interacts with stars (especially those that are many times the mass of the Sun) as they form and die, and about how the heavy elements that these stars make are transported throughout the galaxy into later generations of stars. The Black Hole Mapper will observe many thousands of galaxy clusters and supermassive black holes in the distant Universe.  Because light from these objects left when the Universe was much younger, we can use these data to “watch” how these objects grow, change, and influence other galaxies across cosmic time.

An artist conception of the 3D Universe that SDSS-V will explore. The Earth, in the Milky Way, is at the center, and scientists peer outwards in all directions to measure the light from nearby galaxies and distant black holes. Image Credit: Robin Dienel/OCIS.


One of the classic symbols of SDSS is its “plates” — big disks of aluminum that hold the hand-plugged fiber optic cables up to our 2.5-meter telescopes.  These plates can be thought of as mini maps of the sky, with holes punched through them at the locations of the stars and galaxies we want to observe.  But all of that is changing in SDSS-V, in two major ways.  First, we’re building a couple of small telescopes to add to the ones that already exist, which the Local Volume Mapper will connect directly to six brand-new instruments for taking their measurements.  Second, SDSS-V is replacing its plates with many little robots (500 of ’em!) that are able to position the fiber optic cables anywhere in the focal plane of the telescope.  Unlike fibers plugged into the plates, the robots can move from target to target during an observation, allowing the survey to observe each star, quasar, or galaxy cluster only as long as needed and to be much more efficient.  We’ll miss our beautiful plates, but robots are pretty cool too, right?

All three Mappers will operate instruments in both hemispheres — on SDSS’s trusty 2.5-meter Sloan Telescope at Apache Point Observatory in New Mexico, USA, and on the 2.5-meter du Pont Telescope and the new small telescopes at Las Campanas Observatory in Chile.  (SDSS-IV has already established an important presence at Las Campanas.)  By using both sites, SDSS-V will have a spectroscopic view of the entire sky, because no single place on Earth can see everything.  Even though each Mapper has different science goals, SDSS scientists from all of the Mappers will continue to meet together regularly and share results, because we’re all interested in the same Universe!

SDSS-V can’t happen without the support of member institutions, though.  So if you are (or if you know) an astronomer who wants to be part of making it happen and have early access to the data and the global network of collaborators within SDSS, talk to your chair or director, and let us know how we can help!

SDSS in the Numbers

Scientists are inordinately fascinated by the turning over of odometers.  SDSS has recently passed three such milestones.  A list of all published refereed papers that mention “SDSS” or “Sloan Survey” in their title and abstract (link to the: custom ADS query) finds that:
-We have just passed 8000 published papers (8009 to be exact);
-We have just passed 400,000 total citations (401,609 to be exact);
-The paper that introduced SDSS to the world, York et al, has just hit 6000 citations.

A few other fun statistics:
-We have 90 papers with 500 or more citations;
-The survey’s h number is 242 (there are 242 papers with 242 or more citations);
-There are 849 papers with 100 or more citations.

This information was contributed by Prof. Michael Strauss (Princeton), Former Project Spokesperson and Deputy Project Scientist in SDSSI/II.

A Visit to Las Campanas

Following the 2017 SDSS Collaboration Meeting, a small number of the scientists in attendance travelled to La Serena, to the North of Santiago, to participate in a trip to Las Campanas, where the APOGEE-2S instrument has been installed on the Irene du Pont Telescope. We made our own way to La Serena (by plane, or overnight bus) and met at 9.30am in the La Serena Plaza del Arms to travel to Las Campanas together.

We started our journey under thick cloud, but quickly climbed out of it for spectacular views of the Chilean Andes.

Finally Las Campanas is visible in the distance (spot the speck on the mountain).

Las Campanas is just visible as a speck on a mountain to the right of centre. Credit: Karen Masters, SDSS.

We arrived at Las Campanas around lunchtime, for a quick meal, before touring both the Irene du Pont Telescope, and the Clay 6.5 Meter Telescope (one of the two Magellan Telescopes).

Both the Magellan Telescope (right) and the du Pont Telescope (left) on Las Campanas. Credit: Karen Masters, SDSS.

We were of course especially interested to see the APOGEE infrastructure, now installed in the Irene du Pont Telescope.

Plug plate storage at the du Pont Telescope. Credit: Karen Masters, SDSS.

The APOGEE-2S Instrument. Credit: Karen Masters, SDSS

Then it was back to La Serena to head out many different ways home. Scientists from as far apart as China, Mexico, the UK, Chile and the USA had joined the trip and enjoyed visiting one of the observatories used by SDSS together.

Group shot outside the du Pont Telescope.

Work for SDSS – Senior Software Developer for Apache Point Observatory

Many people contribute to the success of SDSS, not least the staff working at Apache Point Observatory, where our 2.5m Sloan Telescope is located.

The below job add for a Senior Software Developer to support engineering and observing at Apache Point Observatory is copied from a posting on the New Mexico State University website:

New Mexico State University is seeking a technical and computer-oriented person for a Senior Software Developer position to support daytime engineering and night-time astronomical observing at Apache Point Observatory (APO), in Sunspot, NM. The observatory at Sunspot NM will be location of work place. Work schedule on site is generally M-F 8-4:30.

Responsibilities include; designs, implements/installs, maintains, and administers computer, network, and phone infrastructure including hardware and software. Monitors Zenoss, overall performance to proactively identify potential issues and tune appropriately. Providse 24/7 high reliability systems with security and analysis – splunk and Bro. Performs root cause analysis on failed components and implements corrective measures. Works with others to address problems, implement new instrumentation and capabilities. Internal and external customer support and good communication skills are required. Familiar with cluster and virtual systems.

Relevant experience includes hands-on system administration, computer system and network management and development and system security. Proficiency in Unix/Linux, RedHat KVM, C, Python, VxWorks, RTEMS,FreePBX, Vyatta and VyOS,Mac OS, Modeling language – UML. Technical writing, HTML5, CSS, js, frameworks and nodej applications.

Must be able to work at 9500 ft MSL, provide critical support off hours, holidays and weekends.

Benefits: Group medical, hospital, life, dental, and disability insurance. State educational retirement, workers compensation, sick and annual leave, and unemployment compensation.

Paper/email documents will not be accepted. Required documents (CV/Resume, 3 references, unofficial copy of transcripts) must be attached to the NMSU electronic application system at

Employment is contingent on funding and eligibility for employment in U.S. and results of a background verification. Target start date is July 1, 2017.

Direct link to the posting on the NMSU website:

SDSS-IV at #aas229: Friday Abstracts

Here are the SDSS related abstracts for Friday 6th January at #aas229.


10:00 AM – 10:10 AM
306.01. The SDSS-IV Extended Baryon Oscillation Spectroscopic Survey: The Clustering of Luminous Red Galaxies Using Photometric Redshifts
Abhishek Prakash

10:50 AM – 11:00 AM
302.05. Composite Spectra of Broad Absorption Line Quasars in SDSS-III BOSS
Hanna Herbst; Fred Hamann; Isabelle Paris; Daniel M. Capellupo


347.15. Constraining the Merging History of Massive Galaxies Since Redshift 3 Using Close Pairs. I. Major Pairs from Candels and the SDSS
Kameswara Bharadwaj Mantha et al.

347.34. Correlating The Star Formation Histories Of MaNGA Galaxies With Their Past AGN Activity
Andrea Gonzalez Ortiz

347.35. Incidence of WISE-Selected Obscured AGNs in Major Mergers and Interactions from the SDSS
Madalyn Weston; Daniel H. McIntosh; Mark Brodwin; Justin Mann; Andrew Cooper; Adam McConnell; Jennifer L. Nielson

347.38. Properties of Pseudo-bulges and Classical Bulges Identified Among SDSS Galaxies
Yifei Luo; Aldo Rodriguez; David C. Koo; Joel R. Primack; Sandra M. Faber; Yicheng Guo; Zhu Chen; Jerome J. Fang; Marc Huertas-Company

347.55. Spectral Analysis, Synthesis, & Energy Distributions of Nearby E+A Galaxies Using SDSS-IV MaNGA
Olivia A. Weaver; Miguel R. Anderson; Muhammad Wally; Olivia James; Julia Falcone; Allen Liu; Nicole Wallack; Charles Liu

347.56. A Study of E+A Galaxies Through SDSS-MaNGA Integral Field Spectroscopy
Muhammad Wally; Olivia A. Weaver; Miguel R. Anderson; Allen Liu; Julia Falcone; Nicole L. Wallack; Olivia James; Charles Liu

336.04. Results from a Pilot REU Program: Exploring the Cosmos Using Sloan Digital Sky Survey Data
Nancy J. Chanover; Kelly Holley-Bockelmann; Jon A. Holtzman

336.05. The FAST Initiative: Fostering a More Inclusive SDSS Collaboration
Kelly Holley-Bockelmann; Nancy J. Chanover; Adam J. Burgasser; Kelle L. Cruz; Charles Liu; Paul A. Mason; Jesus Pando; Emily L. Rice; Sarah J. Schmidt; Jose R. Sanchez-Gallego; Sara Lucatello; Alfonso Aragon-Salamanca; Francesco Belfiore; Brian Cherinka; Diane Feuillet; Amy Jones; Karen Masters; Audrey Simmons; Ashley Ross; Keivan G. Stassun; Jamie Tayar

343.01. The Open Cluster Chemical Abundances and Mapping (OCCAM) Survey: Overview and Membership Methods
John Donor; Peter M. Frinchaboy; Julia O’Connell; Katia M. Cunha; Benjamin A. Thompson; Matthew Melendez; Matthew D. Shetrone; Steven R. Majewski; Gail Zasowski; Carlos Allende-Prieto; Marc H. Pinsonneault; Alexandre Roman-Lopes; Mathias Schultheis ; Keivan G. Stassun

343.02. The Open Cluster Chemical Abundances and Mapping (OCCAM) Survey: Galactic Gradients using SDSS-IV/DR13 and Gaia
Peter M. Frinchaboy; John Donor; Julia O’Connell; Katia M. Cunha; Benjamin A. Thompson; Matthew Melendez; Matthew D. Shetrone; Steven R. Majewski; Gail Zasowski; Carlos Allende-Prieto; Ricardo Carrera; Ana García Pérez; Michael R. Hayden; Fred R. Hearty; Jon A. Holtzman; Jennifer Johnson; Szabolcs Meszaros; David L. Nidever; Marc H. Pinsonneault; Alexandre Roman-Lopes; Ricardo P. Schiavon; Mathias Schultheis ; Verne V. Smith; Jennifer Sobeck; Keivan G. Stassun

343.03. The Open Cluster Chemical Abundances and Mapping (OCCAM) Survey: Optical Extension for Neutron Capture Elements
Matthew Melendez; Julia O’Connell; Peter M. Frinchaboy; John Donor; Katia M. Cunha; Matthew D. Shetrone; Steven R. Majewski; Gail Zasowski; Marc H. Pinsonneault; Alexandre Roman-Lopes; Keivan G. Stassun

344.18. Searching for Long-Period Companions and False Positives within the APOGEE Catalog of Companion Candidates
Duy Nguyen; Nicholas W. Troup; Steven R. Majewski

344.19. The APOGEE DR13 Catalog of Stellar and Substellar Companion Candidates
Nicholas W. Troup

344.20. APOGEE/Kepler Overlap Yields Orbital Solutions for a Variety of Eclipsing Binaries
Joni Marie C. Cunningham; Diana Windemuth; Aleezah Ali; Meredith L. Rawls; Jason Jackiewicz


This post is now in four languages: English, Chinese, Spanish and Portuguese! It is originally written by Anne-Marie Weijmans in English and translated by Zheng Zheng (to Chinese) ,  Andres Meza (to Spanish) and Ricardo Ogando (to Portuguese). 

This weekend, the Sloan Digital Sky Survey (SDSS) is celebrating its thirteenth public data release, or lucky DR13!

Data releases are an important part of the SDSS. All the data that are observed by the Sloan Telescope for the various surveys that are part of SDSS, get reduced and processed, and eventually are made publicly available. This means that everyone with access to the internet can download the data, use it for their research or teaching, or simply look at all the images and spectra that are available. You just have to go to the SDSS website, and you can start exploring the data for yourself!

So, what does DR13 have in store for you? Apart from including all the data that was released in previous data releases, there is also lots of new data:

  • DR13 is the first data release for the MaNGA survey! MaNGA stands for Mapping Nearby Galaxies at Apache Point Observatory, and it studies galaxies with integral-field spectroscopy. This allows us to study chemical elements and motions of stars and gas not just in the centre of the galaxies, but all over the galaxy outskirts too. MaNGA is releasing its spectra in datacubes for 1351 individual galaxies, making it the biggest integral-field galaxy survey available on-line so far!
  • APOGEE, or the APO Galaxy Evolution Experiment is taking infra-red spectra for hundreds of thousands of stars in the Milky Way. For this data release, they have improved the analysis of all their previously released spectra, and measured the abundances of various chemical elements of stars. This will help us understand how the Milky Way formed over time.
  • eBOSS, short for extended Baryon Oscillation Spectroscopic Survey, is mapping the structure of the Universe, by taking spectra of more than a million galaxies and quasars. Its goal is to measure the expansion rate of the Universe, and the nature of the mysterious Dark Energy that accelerates this expansion. eBOSS is releasing improved analysis of previously released spectra, as well as several catalogs with information on emission line galaxies and variable quasars.

Do you want to have a look at all of this data? Here are some places to get started:

  • The SDSS SkyServer has several tools to explore the data. You can for instance:
    • find stars and galaxies in the Navigate tool
    • look at images and spectra of stars and galaxies with the QuickLook tool
    • search for a particular sample of galaxies or stars with SQL
  • If you are interested in analyzing the data yourself, then you can find more information on how to download the data on the SDSS data access page
  • If you are a teacher and interested in activities that will help your students explore the Universe, then have a look at our SDSS education web page, with lots of resources for the class room.

Anne-Marie Weijmans
SDSS Data Release Coordinator
University of St Andrews






  • DR13是MaNGA巡天的第一次数据释放!MaNGA是对近邻星系进行的积分场光谱巡天。有了MaNGA数据,我们还可以研究整个星系的 — 而不仅仅是星系中心的 — 元素丰度以及恒星和气体的运动。 MaNGA将释放1351个星系的IFU光谱,这也是现今在网上公开的最大的积分场星系巡天数据样本。
  • APOGEE是拍摄几十万颗银河系内恒星的红外光谱的巡天项目。在这次的数据释放中,我们改进了以前的数据处理方式,并且测量了恒星的各种元素丰度。这将会帮助我们理解银河系的形成过程
  • eBOSS巡天用拍摄一百多万个星系和类星体的光谱的方式来描绘宇宙的结构。它的目的是测量宇宙膨胀的速度以及探寻造成宇宙加速膨胀的神秘的暗能量的本质。eBOSS不光会释放经过改进处理的以前释放过的光谱,还会释放几个包含发射线星系和变源类星体信息的星表。


  • 如果你希望自己来分析数据,那么你可以在SDSS数据使用页面找到如何下载数据的相关信息
  • 如果你是一名教师并且希望利用一些活动帮助学生探索宇宙,那么你可以查看SDSS教育网站,这里面有很多相关资源可以帮助课堂教学。



Este fin de semana, Sloan Digital Sky Survey (SDSS) está celebrando su décimo tercera liberación de datos públicos o ¡afortunado DR13!

La liberación de datos es una parte importante de SDSS. Todos los datos que son observados por el Telescopio Sloan para los distintos estudios que forman parte de SDSS, son reducidos y procesados, y eventualmente puestos a disposición del público. Esto significa que cualquier persona con acceso a Internet puede bajar los datos, usarlos para su investigación, para enseñar o simplemente para ver las imágenes y los espectros que están disponibles. Sólo tienes que ir al sitio web de SDSS y ¡ya puedes comenzar a explorar los datos por ti mismo!

¿Qué tiene DR13 para ti? Además de incluir todos los datos que ya han sido hechos públicos anteriormente, también hay una gran cantidad de nuevos datos:

  • ¡DR13 es la primera liberación de datos para MaNGA! MaNGA es el acrónimo en inglés para Mapeo de Galaxias Cercanas desde el Observatorio de Apache Point, y estudia galaxias con espectroscopia de campo integral. Esto nos permite estudiar los elementos químicos y el movimiento del gas y la estrellas no solo en el centro de las galaxias, sino que también en sus partes externas. MaNGA está liberando sus espectros en cubos de datos para 1351 galaxias individuales, ¡convirtiéndolo en el estudio de campo integral más grande disponible en línea!
  • APOGEE, o experimento de Evolución Galáctica en el APO de sus siglas en inglés, está tomando espectros infrarrojos para cientos de miles de estrellas en la Vía Láctea. Para esta liberación de datos, se ha mejorado el análisis de todos los espectros publicados previamente y medido la abundancia de varios elementos químicos de las estrellas. Esto nos ayudará a entender cómo se ha formado la Vía Láctea en el tiempo.
  • eBOSS, acrónimo en inglés para Muestra Espectroscópica Extendida de la Oscilación Bariónica, está haciendo un mapa de la estructura del Universo, tomando espectros de más de un millón de galaxias y quásares. Su objetivo es medir la tasa de expansión del universo y la naturaleza de la misteriosa Energía Oscura que acelera su expansión. eBOSS está liberando análisis mejorados de sus espectros anteriores, así como también varios catálogos con información para las galaxias con líneas de emisión y quásares variables.

¿Quieres darle un vistazo a todos estos datos? Aquí hay algunos lugares para comenzar:

  • El SDSS SkyServer tiene varias herramientas para explorar los datos. Tu puedes por ejemplo:
    • Encontrar estrellas y galaxias con la herramienta Navigate.
    • Ver las imágenes y espectros de estrellas y galaxias con la herramienta QuickLook
    • Buscar un grupo particular de estrellas y galaxias con SQL.
  • Si eres un profesor y estás interesado en actividades que puedan ayudar a tus estudiantes a explorar el Universo, puedes mirar nuestra página de educación del SDSS donde hay muchos recursos para realizar en las clases.




Esse final de semana, o Sloan Digital Sky Survey (SDSS) celebra seu décimo terceiro lançamento de dados ao público, ou um sortudo DR13!

Os Lançamentos de Dados são uma parte importante do SDSS. Todos os dados que são observados pelo telescópio Sloan, para os vários levantamentos que são parte do SDSS, são reduzidos e processados, e em algum momento são disponibilizados para o público. Isso significa que qualquer pessoa com acesso à internet pode baixar esses dados, usar para sua pesquisa ou ensino, ou simplesmente olhar as imagens e espectros disponíveis. Basta ir à página do SDSS e começar a explorar!

Bom, mas o que é que o DR13 tem? Além dos dados de todos os lançamentos anteriores, um montão de novidades foram incluídas:

  • DR13 é o primeiro a conter dados do levantamento MaNGA! MaNGA significa Mapeamento de Galáxias Próximas no Observatório de Apache Point (em inglês, Mapping Nearby Galaxies at Apache Point Observatory), e estuda galáxias usando espectroscopia de campo integral. Isso nos permite estudar os elementos químicos e o movimento das estrelas e do gás não apenas no centro de galáxias, mas também em sua periferia. MaNGA está liberando seus espectros em cubos de dados para 1.351 galáxias, fazendo dele o maior levantamento disponível online de galáxias observadas com campo integral até hoje.
  • APOGEE, ou o Experimento de Evolução da Galáxia no APO (em inglês, APO Galaxy Evolution Experiment) está observando espectros no infravermelho para centenas de milhares de estrelas na Via-Láctea. Nesse lançamento de dados eles melhoraram a análise de todos os espectros liberados anteriormente, medindo a abundância de vários elementos químicos nas estrelas. Isso vai nos ajudar a entender como a Via-Láctea se formou e evoluiu ao longo do tempo.
  • eBOSS, abreviação de extended Baryon Oscillation Spectroscopic Survey, está mapeando a estrutura do Universo, observando espectros de mais de um milhão de galáxias e quasares. Seu objetivo é medir a taxa de expansão do Universo, e a natureza da misteriosa Energia Escura que acelera essa expansão. eBOSS está disponibilizando análises melhoradas de espectros liberados anteriormente, além de vários catálogos com informação sobre galáxias com linhas de emissão e variabilidade de quasares.

Você quer dar uma olhada em todo esse conjunto de dados? Por onde começar:

  • O SkyServer do SDSS tem várias ferramentas para explorar os dados. Você pode, por exemplo:
    • encontrar estrelas e galáxias usando o Navigate
    • olhar imagens e espectros com o QuickLook
    • procurar por uma amostra de galáxias ou estrelas em particular usando SQL
  • Se você está interessado em analisar os dados você mesmo, você pode encontrar mais informações de como baixar os dados na página SDSS data access
  • Se você for um professor e está interessado em atividades que possam ajudar seus estudantes a explorar o Universo, dê uma olhada em nossa página educativa, com vários recursos para a sala de aula.



It takes a large team of people to put together a data release: from collecting the data at the telescopes, to processing the data, analyzing the data, and documenting the data. The SDSS DR13 website, that describes all the various datasets now available in DR13, was mostly written at DocuFeest, by a dedicated group of SDSS scientists. Image credit: Jennifer Johnson.  数据释放要经过很多环节:从望远镜收集数据、处理数据、分析数据、以及准备相关文档,这是我们大团队共同努力的结晶。SDSS DR13网站描述了DR13中包含的所有数据,这个网站大部分都是由一批SDSS科学家在DocuFeest上完成的。照片由Jennifer Johnson提供 Se debe reunir un grupo grande de personas para generar los datos públicos: desde recolectar los datos en los telescopios, luego procesar y analizar los datos, hasta finalmente documentarlos. El sitio para el DR13, que describe todos los conjuntos de datos ahora disponibles, fue escrito en su mayor parte en el DocuFeest por un grupo dedicado de científicos de SDSS.  Concluir um lançamento de dados requer um grande time de pessoas: da coleta de dados nos telescópios, ao seu processamento, análise, e documentação. A página do DR13 do SDSS, que descreve todos os distintos conjuntos de dados agora disponíveis no DR13, foi quase toda escrita por um dedicado grupo de cientistas do SDSS numa reunião batizada de DocuFeest (Feest é festa em holandês, origem de uma das organizadoras do evento de documentação). Crédito da imagem: Jennifer Johnson.


Caption: all the SDSS data are stored at the servers of the Center for High Performance Computing (CHPC[]), at the University of Utah. This particular server holds all the SDSS data releases, including DR13. The total data volume is about 267 TeraBytes (TB = 1000 Gigabyte = 1012 bytes): that is more than 58,000 DVDs worth of data! Image credit: Adam Bolton.

All the SDSS data are stored at the servers of the Center for High Performance Computing (CHPC), at the University of Utah. This particular server holds all the SDSS data releases, including DR13. The total data volume is about 267 TeraBytes (TB = 1000 Gigabyte = 1012 bytes): that is more than 58,000 DVDs worth of data! Image credit: Adam Bolton.  所有的SDSS数据都存储在美国犹他大学高性能计算中心(CHPC)的服务器上。这台服务器存储着所有SDSS释放过的数据,包括DR13。整个数据容量大约是267T (1T=1000G=1012 bytes):这比58000张DVD包含的数据都要多!照片由Adam Bolton提供 Todos los datos de SDSS están almacenados en los servidores del Centro de Computación de Alto Rendimiento de la Universidad de Utah. Este servidor contiene todos los datos públicos, incluyendo DR13. El volumen total de datos es de alrededor de 267 TB, ¡esto es más de 58.000 DVDs!  Todos os dados estão armazenados em servidores no Center for High Performance Computing (CHPC), na University of Utah. Esses servidores em particular contem todos os lançamentos de dados do SDSS, incluindo o DR13. O volume total de dados é de cerca de 267 Terabytes (TB = 1000 Gigabyte = 1012 bytes): isso é mais que 58.000 DVDs cheios de dados! Crédito da imagem: Adam Bolton.



The very first 17 galaxies observed by MaNGA, one plate full! These galaxies are all included in DR13. Some galaxies have been off-set from the centre of the IFU to allow inclusion of foreground stars, to test our measurement precisions (this was only done for this first commissioning plate). Image credit: Kevin Bundy.  这17个星系来自MaNGA的首次观测,是在同一个光纤插板上的所有星系!这些星系都包含在DR13里面。有些星系偏离了IFU的中心,这是因为我们要同时拍摄一些前景恒星用来检测测量精度 (不过这种情况只发生在这第一个光纤插板上)。照片由Kevin Bundy提供 ¡Las primeras 17 galaxias observadas por MaNGA en una sola placa! Todas estas galaxias están incluidas en el DR13. Algunas galaxias han sido desalineadas del centro del IFU para incluir estrellas en el fondo, las cuales permiten probar la precisión de las mediciones (esto fue hecho sólo para esta primera placa).  As 17 primeiríssimas galáxias observadas pelo MaNGA, são um verdadeiro gol de placa! Essas galáxias foram todas incluídas no DR13. Algumas galáxias foram deslocadas do centro do IFU para incluir estrelas, a fim de testar a precisão de nossas medidas (isso foi feito apenas para essa placa inaugural de comissionamento do instrumento). Crédito da imagem: Kevin Bundy.

An artist view of the universe 艺术家眼里的宇宙

Recently, a Chinese artist, Jian Yang, organized his personal exhibition in Beijing, China. The exhibition is called “the beginning of infinity” and one of his art pieces showed in this exhibition has a component made of an SDSS plate.

最近中国的一位艺术家杨健在北京进行了一次个人艺术展。这次展出的名字叫 “无穷的开始”,而其中的一件艺术品是利用了SDSS的一块光纤插板做成的。

The room holding the exhibition was designed as a maze. The art piece with the SDSS plate was placed at the center of a maze. It is named “The Universe” and the idea came from an old fairy tale: The earth is a big whale and the sky is a huge elephant. If you could find a leg of the elephant and climb up along the leg, then you could grab the stars. In the artist’s view, the SDSS telescope is trying to capture and analyze the starlight. So he combined science and the fairy tale by putting the SDSS plate at the bottom of the flying elephant’s leg, which means the plate could help us climb up and reach the stars.



The room holding the exhibition was designed as a maze.

The room holding the exhibition was designed as a maze. 整个展览场地被设计成一个迷宫的形式。


The art piece with an SDSS plate (plate# 3939).

The art piece with an SDSS plate (plate# 3939). The plate (编号3939) is placed at the bottom of an elephant’s leg. 用SDSS光纤插板做成的艺术品. SDSS的板子被当做大象的脚底板。


The art piece viewed from the bottom.

The art piece viewed from the bottom. 从下面看这件艺术品。

What is MaNGA (in one sentence)?



Some months ago, members of the MaNGA (Mapping Nearby Galaxies at Apache point observatory) survey (part of SDSS-IV) were asked to suggest ideas for a suitable taglines/catchphrase which would describe the survey in one sentence. This idea was that this would go on promotional materials SDSS-IV would take to the American Astronomical Society Meeting, and also the main SDSS website.

The working favourite to that point had been “the galaxy survey for people who love galaxies”, but we wanted something which described the scientific goals of the survey more precisely.

In the word of MaNGA PI, Kevin Bundy this request resulted in an “outpouring of creative, collective genius” (a phrase which Kevin suggested might itself be the appropriate one to describe the MaNGA team).

Here are some of the ideas the team came up with, catagorised by Kevin:

Ideas which reference The 3rd Dimension

  1. .. Now in 3D!
  2. Sloan goes 3D
  3. Sloan Galaxies in three dimensions
  4. Galaxies in 3D
  5. A new dimension in galaxy surveys
10 000 (nearby) galaxies mapped in 3D
  6. A multi-dimensional view of galaxies
  7. Galaxies in 3D by the thousands
  8. Thousands of local galaxies in 3D
  9. Ten thousand Galaxies. Three dimensions

Inspirational ideas

  1. To boldly go where no other Galaxy survey has gone before.
  2. Unravelling the galaxy avatar
  3. Ten thousand mysteries unfold

Direct (or descriptive) ideas:

  1. Census of local galaxies
  2. MaNGA: Deciphering galaxies pixel-by-pixel
  3. Observing the dynamical structures and composition of galaxies to unravel their evolutionary histories
  4. Galaxy birth, assembly, growth and ‘death’
  5. Galaxies Beyond the Central Fiber
  6. Spatially resolved spectroscopy of 10,000 nearby galaxies

Ideas Inspired by Biological Analogies

  1. Galaxy dissection
  2. Galaxies under the microscope
  3. Exploring the life cycle of galaxies
  4. Anatomising galaxies dead and alive
  5. Dissecting galaxies in their dark matter haloes

Humorous suggestions

  1. Galaxies do the full monty
  2. Everything you wanted to know about galaxies, and in 3D
  3. Experience galaxies in 3D, without the glasses

Clever/cultural references

  1. Taking spectra of the spectrum of galaxies
  2. Galaxies in 3D! It’s over 9000!!
  3. 10K3D
  4. How galaxies tick

The final decision was made to go with “Mapping the inner workings of thousands of nearby galaxies” for our website, and we have a banner which says “The 3D Lives of Galaxies”, although we also really like the creative idea of making an API to return all of these randomly.

MaNGA - Mapping the inner workings of thousands of nearby galaxies


Many thanks to: Jeff Newman, Bob Nichol, Kyle Westfall, Surhud More, Karen Masters, Aaron Dutton, Claire Lackner, Mike Merrifield, Daniel Thomas, Eric Emsellem, Carles Badenes, Anne-Marie Weijmans, Brian Cherinka, Demitri Muna, Brett Andrews, Christy Tremonti and Kevin Bundy for contributing ideas.


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

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.

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.

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!

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.

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. 

David Schlegel Wins an Ernest Lawrence Award

Prof. David Schlegel of Lawrence Berkeley National Laboratory, the PI of the BOSS part of SDSS-III and a long time contributor to all areas of the Sloan Digital Sky Surveys was announced yesterday as one of the winners of the E.O. Lawrence Award.

David Schelegel, PI of BOSS, shows off a plug plate. Image credit: LBL

David Schelegel, PI of BOSS, shows off a plug plate. Image credit: LBL

The Ernest Orlando Lawrence Award was established in 1959 in honor of Ernest Lawrence, who invented the cyclotron (for which he won 1939 Nobel Laureate in physics). The Lawrence Award honors U.S. scientists and engineers, at mid-career, for exceptional contributions in research and development supporting the Department of Energy and its mission to advance the national, economic and energy security of the United States.

The citation for David’s award (for the High Energy Physics Category of the award) reads:

Honored for his exceptional leadership of major projects making the largest two-dimensional and three-dimensional maps of the universe, which have been used to map the expansion rate of the Universe to 10 billion light years and beyond. His fundamental technical contributions to high precision measurements of the expansion history of the Universe, and his massive galaxy redshift surveys to detect baryon acoustic oscillations, has helped ascertain the nature of Dark Energy, test General Relativity, and positively impact fundamental understanding of matter and energy in the universe.  These efforts have made precision cosmology one of the most important new tools of high-energy physics.

All of us at SDSS are delighted to wish David Schlegel many congratulations for this honor.

Heroes of the Helpdesk

They come in a steady stream: the requests for lost passwords, for aid in correcting a CasJobs query, for insight into the technical details of SDSS photometry, astrometry, and spectroscopy, for help with educational resources and SkyServer, and for general astronomical and database knowledge, all sent to Two or three times a day, they appear in the mailboxes of those on the helpdesk mailing list, representing the hopes and dreams of an astronomer, amateur, student, or professional, to use SDSS data to answer the big questions of the Universe (or at least to get more room on the server).

The helpdesk in action: Ben Weaver making SDSS science possible for yet another scientist.

The helpdesk in action: Ben Weaver making SDSS science possible for
yet another scientist.

The task falls to the volunteers, headed up and organized by Ben Weaver, Archive Scientist at New York University (right). Most questions are handled quickly by Ben, Ani Thakar, Archive Scientist at Johns Hopkins University, or Jordan Raddick, one of our Education Directors, also at Johns Hopkins. Promptness is easiest if the questioners have done us the kindness of including relevant information such as the context or URL they are using and the exact query. Occasionally questions about how parameters were derived or why there are changes between Data Releases requires the advice of other SDSS experts. In this case, Ben sends email to the relevant SDSS mailing list. Excellent answers are gratefully accepted from the wider collaboration, who really do know these data. Our thanks to everyone who has stepped up and contributed to making SDSS data scientifically valuable to an astonishing array of people. Above all, we wish to thank the helpdesk regulars. If you have sent an email to the helpdesk or if you know someone who has sent an email to the helpdesk (and you probably do, trust me), send a cheer their way.

Spotlight on APOGEE: Jo Bovy and the Motion of the Sun

The spotlight this month is on Jo Bovy, a John Bahcall Fellow and Long-term Member at the Institute for Advanced Study in Princeton. He completed his PhD at New York University. Within APOGEE, he is the Science Working Group Chair for APOGEE-1, and therefore coordinates the scientific analysis of the APOGEE dataset.


Jo uses big datasets from numerous surveys to understand how the Milky Way came to be. To do this, he studies how stars move and what are their chemical compositions. When he first tackled APOGEE’s huge database of stellar spectra in 2011, he realized that APOGEE’s spatial coverage of the Milky Way’s disk allowed the circular velocity of stars in the Milky Way to be measured with greater accuracy than had ever been done before. (The circular velocity is the speed at which a star orbits the center of the Galaxy. This number changes as a function of distance from the center, and precise measurements are required to correctly determine, for instance, the Galaxy’s mass, but also to measure peculiarities in stellar velocity, which help us determine where it might have originated.) The data analysis in his paper is complex, but he was able to draw two important and straight forward conclusions from this work:

  1. that the circular velocity near the Sun (what we call the “solar neighborhood”), at a distance of 26,000 light-years from the center of the Galaxy, is 218 ± 6 km/s; and
  2. that the Sun itself is moving 25 km/s faster than other stars at the same distance.

The first result was expected: although the circular velocity in the Sun’s neighborhood was assumed to be about 220 km/s for the last 30 years or so, Jo’s was the first precise measurement to confirm this value. The second result, however, was a surprise: previous measurements had pegged the Sun’s motion relative to nearby stars at something like 12 km/s, not 25 km/s. This result was confirmed using a sub-set of APOGEE data (a mere 19,937 stars, or about 15% of the full APOGEE dataset) known as the APOGEE Red Clump Catalog.

Why does this seemingly small difference matter? From an outsider’s perspective, going from 12 km/s to 25 km/s is still only changing from about 5% to 10% of the circular speed, so either result might seem acceptable! But is is important, and Jo explains why: We orbit the Sun, and the Sun orbits the center of the Galaxy just like every other star. Therefore, every speed that we measure for another star is relative to our own motion. If we can understand how we move in the Galaxy, then we will have a much better understanding of the dynamics of the entire Milky Way.

And understanding the Milky Way is, after all, the whole point!

Spotlight on APOGEE: Duy Nguyen and Binary Stars

We are beginning a series of spotlights on APOGEE team members, with special emphasis on their interests in APOGEE science. This month, the spotlight is on Duy Nguyen, one of APOGEE’s postdocs. He graduated from the University of Toronto with a PhD in astronomy and astrophysics, and then held postdoc positions at the University of Florida, Stockholm University, and the University of Rochester before joining the APOGEE team.


Duy’s research is on the subject of binary stars. A binary star is actually two stars orbiting each other. The sizes of the binary star orbits are small enough that the two stars cannot usually be distinguished in images. This can confuse the interpretation of starlight; and in a survey like APOGEE where precise velocities of stars are so important, this can be a big hindrance. As a result, a number of different methods have been employed to try to tease out whether a star is a binary or not.

But this post isn’t just about binary stars — it’s about one scientist’s research into better understanding them! And in many ways, Duy sees APOGEE as the best available experiment for binary star studies. APOGEE takes multiple spectra of most stars in its sample over months and even years, and this time sampling enables orbital periods to be measured. APOGEE’s high spectral resolution means that tiny Doppler shifts in a star’s spectral lines can be measured precisely. And most importantly, such a large sample as APOGEE has observed (more than 150,000 stars to date) means that we may be able to get a better handle on the “binary fraction” of stars in the Milky Way — a problem that has been plaguing modern astronomers for decades.

Duy is primarily interested in the dynamic properties of binary stars. These dynamics are primarily observed by means of the Doppler shift. As the stars in the binary pair orbit one another, each star approaches and recedes from the Earth once per orbit. Every time they approach the Earth, their spectral lines move to a slightly smaller (or “bluer” to use astronomical lingo) wavelength. And every time the star recedes, the spectral lines move to a redder wavelength. These small changes can be detected with APOGEE, and the radial velocity variations of the stars can be determined based on how large is the wavelength shift.

Duy and his collaborators are amassing radial velocity information on the stars in the APOGEE sample, looking for candidates with substantial radial velocity shifts. When they find one, they fit the data points with an orbital model to determine what the most likely stellar masses are. Here is an example fit:


On the x-axis is the time in days, and on the y-axis is the velocity of the star relative to the Sun. This plot shows that the best fit to these data suggest that two stars, one that is at least 0.21 times the mass of the Sun and the other that is 1.6 times the mass of the Sun, are orbiting one another every 112.98 days at a distance greater than 0.065 A.U. It’s interesting to note that the less massive star in this binary is eight times smaller than its companion. Large mass discrepancies in binaries are typical, so that one star dominates the other in terms of brightness. This is one reason why binaries are so difficult to detect.

To date, about 12,000 possible stellar binaries from the APOGEE sample have been flagged based on radial velocity shifts, and 4,000 of these are of special interest because they have been visited seven or more times and exhibit significant radial velocity changes. Of these, 1,500 indicate stellar mass companions, such as the one figured above. While the 12,000 possible binaries were found automatically, the 1,500 sources with stellar mass companions have all had to be screened by hand — a process that Duy would like to fully automate.

Analyzing APOGEE’s huge repository of stellar spectra will enable the most comprehensive assessment of binary stars, including details about whether binary star characteristics are different across the Galaxy. And as an added bonus, APOGEE is sensitive enough to spot Jupiter-sized planets using these methods! How many planets are lurking in the APOGEE dataset?

Special thanks to N. Troup, D. Chojnowski, and S. Majewski for assistance preparing this post.