APOGEE-South: Plate-Pluggers and Tripods – APOGEE-Sur: Conexión de Placas y Trípodes

Recently, a small group of astronomers from Chile has been visiting Apache Point Observatory. Their job will be to assist with operations at APOGEE-South, which is being built for the Irénée du Pont telescope at Las Campanas Observatory. Introducing: Christian Nitschelm, a faculty member at Universidad de Antofagasta; Andrés Almeida, a Masters student from Universidad Andrés Bello; and Jaime Vargas, Masters student at Universidad de La Serena.

Recientemente, un pequeño grupo de astrónomos de Chile ha estado visitando el Observatorio Apache Point (APO por sus siglas en Inglés). Su trabajo consistirá en ayudar con las operaciones en APOGEE-Sur, que se está construyendo para el telescopio Irénée du Pont en el Observatorio Las Campanas. Presentamos a: Christian Nitschelm, profesor en la Universidad de Antofagasta; Andrés Almeida, un estudiante de Maestría de la Universidad Andrés Bello; y Jaime Vargas, estudiante de Maestría de la Universidad de La Serena.

Jamie (left) Christian (center), and Andres (right), unplugging an APOGEE plate after observations. Jamie (a la izquierda), Christian (al centro), y Andrés (a la derecha), desconectando las fibras ópticas de una placa de APOGEE después de las observaciones.

Jamie (a la izquierda), Christian (al centro), y Andrés (a la derecha), desconectando una placa de APOGEE después de las observaciones.
Jamie (left) Christian (center), and Andres (right), unplugging an APOGEE plate after observations.

While at APO, Jamie, Christian, and Andres are learning a number of important skills that they will take back to Las Campanas Observatory. This includes plugging and unplugging plates:

Mientras tanto en el APO, Jamie, Christian y Andrés están aprendiendo una serie de técnicas importantes que llevarán al Observatorio Las Campanas. Esto incluye conectar y desconectar las placas:

Christian and Jamie seen here plugging fibers into a plug plate. Christian y Jaime se ven aquí conectando las fibras en una placa de conexión.

Christian y Jaime se ven aquí conectando las fibras ópticas en una placa de conexión.
Christian and Jamie seen here plugging fibers into a plug plate.

They are also learning to use the new Mock Up and Training Facility tripod, cartridge, and dolly (seen below). This setup will be sent down to Universidad de La Serena so that this crew can train future support staff.

También están aprendiendo a usar la maqueta y trípode de capacitación, el cartucho y carro (observados a continuación). Esta configuración se enviará a la Universidad de La Serena para que este equipo de trabajo pueda entrenar el personal de apoyo futuro.

Christian and Jamie swapping out a plug plate cartridge with the Mock Up and Training Facility tripod (the big steel frame), cartridge (the blue object suspended from the tripod) and dolly, which will be used to transport plug plates to and from the telescope. Christian y Jaime intercambiando el cartucho de la placa conexión con la maqueta y el trípode de capacitación (la estructura de acero grande), el cartucho (el objeto azul suspendido del trípode) y el carro, que será utilizado para transportar las placas de conexión hacia y desde el telescopio.

Christian y Jaime intercambiando el cartucho de la placa conexión con la maqueta y el trípode de capacitación (la estructura de acero grande), el cartucho (el objeto azul suspendido del trípode) y el carro, que será utilizado para transportar las placas de conexión hacia y desde el telescopio.
Christian and Jamie swapping out a plug plate cartridge with the Mock Up and Training Facility tripod (the big steel frame), cartridge (the blue object suspended from the tripod) and dolly, which will be used to transport plug plates to and from the telescope.

“Torquing” the plug plate slightly is a necessary skill so that it aligns with the field of curvature of the telescope. Using a ring around the plate (shown being attached below), the plate can be bent ever so slightly:

“Torcer” ligeramente la placa de conexión es una habilidad necesaria para alinear la placa con el campo de curvatura del telescopio. Usando un anillo alrededor de la placa (mas abajo se ve como se engancha), ésta se puede doblar ligeramente:

Christian and Andres attaching the bending ring around the plate. Christian y Andrés enganchan el anillo de flexión alrededor de la placa.

Christian y Andrés enganchan el anillo de flexión alrededor de la placa.
Christian and Andres attaching the bending ring around the plate.

And, of course, it is important to check your work. In this case, a computer is used to map the locations of fibers on the plate, ensuring that they will be on target when the plug plate is used on the telescope:

Y, por supuesto, es importante revisar su trabajo. En este caso, se utiliza un ordenador para mapear las ubicaciones de fibras en la placa, asegurando que van apuntar al objeto cuando la placa de conexión se use en el telescopio:

20150528_084335

Christian utiliza una computadora para medir el perfil de la placa de conexión después de que ha sido mapeada. Esto asegurará que la placa ha sido “torcida” correctamente.
Christian using a computer to measure the profile of the plug plate after it has been mapped. This will ensure that they have “torqued” the plate properly.

Jamie is enjoying his new skills set! Here, he is drawing an overlay on a plug plate to prepare it for plugging. ¡Jaime disfruta de sus nuevas habilidades! Aquí está dibujando una superposición en una placa de conexión para prepararla para la conexión.

¡Jaime disfruta de sus nuevas habilidades! Aquí está dibujando una superposición en una placa de conexión para prepararla para la conexión.
Jamie is enjoying his new skills set! Here, he is drawing an overlay on a plug plate to prepare it for plugging.

Engineering Work for APOGEE-South – Trabajo de ingenieria en APOGEE-Sur

Telescopes at LCO

The du Pont 2.5m telescope on the middle-left, and the pair of Magellan 6.5m telescopes on the right.
El telescopio de 2.5m du Pont al centro hacia la izquierda y los dos telescopios de 6,5m, Magallanes, a la derecha.

A half-dozen SDSS scientists and engineers traveled to Las Campanas Observatory, Chile at the beginning of March to continue work on characterizing the 2.5m du Pont telescope performance in preparation for the first APOGEE-South hardware tests in August. This report is from the SDSS Operations Software Manager John Parejko, who was part of the run (and ended up involved in some hardware tests, against his better judgement!). Translated into Spanish by Verónica Motta, Associate Professor of Astronomy at Valparaiso University.

Las Campanas Observatory currently hosts three “large” telescopes (greater than 2 meters diameter), and a number of 1 meter diameter and smaller telescopes. The 2.5m du Pont telescope (in use since 1977) is a much older telescope than the 2.5m Sloan telescope at APO (in use since 1999), but it is at an excellent site, its optics are still very good–I heard them referred to as “superb” on several occasions–and it has a large field of view. With the assistance of the telescope’s owners–the Carnegie Institution of Washington–SDSS plans to help design improvements to the telescope drive systems so that we can run an APOGEE-South survey and fully sample the Milky Way’s bulge.

Una media docena de científicos e ingenieros del SDSS viajaron al Observatorio Las Campanas (Chile) a principios de marzo para continuar el trabajo de caracterización del rendimiento del telescopio de 2.5m du Pont en preparación para la primera prueba de hardware de APOGEE-Sur que se realizara en agosto. Este informe proviene del Director de Operaciones de Software del SDSS, John Parejko, que participó en la ejecución (y que terminó involucrado en algunas pruebas de hardware, en contra de su mejor juicio ! ). Traducción de Verónica Motta, profesor asociado de astronomía en la Universidad de Valparaíso.

El Observatorio Las Campanas actualmente alberga tres “grandes” telescopios (mayores de 2m de diámetro), y varios más pequeños de hasta 1m de diámetro. El telescopio de 2.5m du Pont (en uso desde 1977) es más antiguo que el telescopio de 2.5m Sloan en el Observatorio Apache Point (APO, en uso desde 1999), pero está en un lugar excelente, su óptica es todavía muy buena -he oído referirse a ella como “excelente” en varias ocasiones- y tiene un gran campo de visión. Con la ayuda de los propietarios del telescopio -la Institución Carnegie de Washington- el SDSS planea ayudar a mejorar el diseño de los sistemas de accionamiento del telescopio de manera que podemos realizar el relevamiento APOGEE-Sur y muestrear completamente el bulbo de la  Vía Láctea.

Paul and Nick looking at the rotator

Paul Harding and Nick MacDonald looking at the rotator.
Nick MacDonald y Paul Harding investigan las propiedades físicas del rotador del du Pont.

In order to determine what improvements the telescope requires, we have to make precise measurements of how different parts of the telescope move. From previous work, we found that the Right Ascension and Declination motors (equivalent to latitude and longitude projected onto the sky) probably don’t need much work. This trip, we measured the motion of the rotator and focus systems. Carnegie is in the process of completing their own upgrades to the telescope, and our measurements will help guide these changes.

Con el fin de determinar qué mejoras necesita el telescopio tenemos que hacer mediciones precisas de cómo se mueven las diferentes partes del telescopio. A partir de trabajos anteriores, encontramos que los motores de la Ascensión Recta y de la Declinación (equivalentes a la latitud y a la longitud proyectada sobre el cielo) probablemente no necesitan mucho trabajo. En este viaje medimos el movimiento del rotador y del sostema de enfoque. Carnegie se encuentra en el proceso de terminar sus propias mejoras al telescopio y nuestras medidas servirán de guía para estos cambios.

Author self portrait in a primary. You can see the reflection of the secondary mirror and its light baffles just above my head.

Author self portrait in a primary. You can see the reflection of the secondary mirror and its light baffles just above my head.
Autorretrato del autor en el primario, se puede ver el reflejo del espejo secundario y su luz que pasa justo por encima de mi cabeza.

To focus a telescope like this one, you move the secondary mirror. Even tiny changes in the position or tilt of the secondary can result in incorrect or uneven focus when you need a large field of view, as APOGEE will. As the du Pont is an older telescope, the system that moves the secondary mirror may not be as stable as APOGEE requires.

We first checked whether the mirror moved the exact amount each time it was commanded. We’ve found that the mirror motors need to be more repeatable: moving 500 “up” and then 500 “down” should return to exactly the same place, but it doesn’t. The Carnegie engineers are now working to improve the motors and control systems to fix this.

Para enfocar un telescopio como éste se mueve el espejo secundario. Incluso pequeños cambios en la posición o en la inclinación del secundario pueden resultar en un foco incorrecto o irregular en un gran campo de visión como el que utilizará APOGEE. Como el telescopio du Pont es viejo, el sistema que mueve el espejo secundario puede no ser tan estable como requiere APOGEE.

Primero revisamos si el espejo se movió la cantidad correcta cada vez que se le ordenó. Hemos encontrado que los motores del espejo tienen que ser más confiables: moverse 500 hacia “arriba” y después 500 hacia “abajo” debería regresarlo exactamente al mismo lugar, pero no es así. Los ingenieros de Carnegie están trabajando para mejorar la motores y los sistemas de control para solucionar este problema.

Author self portrait in the du Pont secondary, with my camera and our measuring target visible.

Author self portrait in the du Pont secondary, with my camera and our measuring target visible.
Autorretrato del autor en el secundario del du Pont, con mi cámara y nuestro objeto de medición visible.

To measure any shift or tilt in the secondary, we used a rather interesting system: a typical camera (the Panasonic G2 that I travel with for touristy photos; it took all the pictures shown in this post) with a long telephoto lens mounted on a moveable rail, taking pictures of the image in the secondary mirror of a “target” on the floor. We then took pictures with the camera and measured whether the target moved around: if it doesn’t move from image to image, we know the secondary is very stable against tilts and shifts during movement. We’re still analyzing the results of these tests, and will use them to detail what changes need to be made.

Para medir cualquier desplazamiento o inclinación en el secundario usamos un método interesante: una cámara típica (la Panasonic G2 con la que viajo para tomar fotos turísticas; la que tomó todas las imágenes que se muestran aquí) con un teleobjetivo largo montado en un carril móvil, toma fotos de la imagen en el espejo secundario de un “objetivo” en el suelo. Entonces tomamos fotos con la cámara y medimos si el objetivo se movió: si no se mueve de imagen a imagen, sabemos que el secundario es muy estable ante las inclinaciones y los cambios durante el movimiento. Todavía estamos analizando los resultados de estas pruebas y las usaremos para detallar los cambios deben hacerse.

Además de mi trabajo de ingeniería en el telescopio du Pont, tuve tiempo durante la noche para fotografiar el cielo austral. Este fue mi primer viaje al hemisferio sur y me aseguré de levantarme temprano al menos una mañana para ver las Nubes Mayor y Menor de Magallanes y toda la gloria de la Vía Láctea austral. Tuve que levantarme temprano para evitar la Luna casi llena, que disminuye la visibilidad. Sin duda tienen cielos espectaculares ahí abajo.

In addition to my engineering work on the du Pont telescope, I was able to take some time at night to photograph the southern sky. This was my first trip to the southern hemisphere, and I made sure to get up early at least one morning to see the Large and Small Magellanic Clouds and the full glory of the southern Milky Way. I had to get up early in order to avoid the nearly-full moon, which otherwise much diminished the view. They’ve certainly got some spectacular skies down there!

The southern hemisphere Milky Way and Large Magellanic Cloud, over the main LCO building.

La Vía Láctea y las Nubes Mayor y Menor de Magallanes Nube en el hemisferio austral, sobre el edificio principal del LCO.
The southern hemisphere Milky Way and Large Magellanic Cloud, over the main LCO building.

Pasé mis últimos días de este viaje en la ciudad de La Serena, reunido con la gente de la Universidad de La Serena (ULS) y reuniendo los resultados de las pruebas. Durante este tiempo, pude ver como la escuela de ingeniería ULS  maniobró la nueva máquina, marca Mazak CNC, con cuidado hasta su lugar en el taller de mecánica. Las instituciones chilenas han utilizado la colaboración SDSS/Chile para reforzar su infraestructura a través de subvenciones y varios acuerdos. En este caso, fueron capaces de comprar el modelo más avanzado de fresadora computarizada que planean utilizar para construir piezas para APOGEE-Sur.Tengo ganas de ver que pueden construir con ella!

I spent my last days of this trip in the city of La Serena, meeting with people at the University de La Serena (ULS) and collating results from the tests. During this time, I was on hand to watch as the ULS engineering school had a brand new Mazak CNC machine carefully maneuvered into place in their machine shop. Chilean institutions have used the SDSS/Chile collaboration to bolster their on-site infrastructure via grants and various agreements. In this case they were able to purchase a state-of-the- art computerized milling machine that they plan to use to construct parts for APOGEE-South. It will also provide engineering student training and experience, and allow the university to construct other cutting edge scientific equipment in the future.

I’m looking forward to see what they can build with it!

Happy Engineers standing in front of their just-delivered CNC machine. Ingenieros felices de pie frente a su recién entregada máquina CNC.

Ingenieros felices de pie frente a su recién entregada máquina CNC.
Happy Engineers standing in front of their just-delivered CNC machine.

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.

bovy

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.

Nguyen

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:

Nguyen_Troup_ScreenShot

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.

APOGEE’s Infrared View of the Stellar Temperature Sequence

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.