Orion Nebula Cluster and long, long codes…ttasnimana | June 27, 2011
Hello, I am Tonima Tasnim Ananna – a Physics and Astronomy major at Bryn Mawr and Haverford respectively and a rising junior. I have so far spent two very exciting weeks at Space Telescope Science Institute (STScI) at Baltimore as an intern this summer. I have been to five astronomy talks in the last two weeks – two of them specifically targeted at the summer interns, and I will talk about them and other ‘perks’ of being a summer intern at STScI in a moment, but first I want to talk about the project I am working on, because it’s exciting and because we can all relate to science.
I am working with astronomer Massimo Robberto and his team of one PhD student and one Post-doc. My project is to sort out 6 catalogues full of information about stars in the Orion Nebula cluster. There are over 6000 stars observed in total, and the observations were made using five cameras – three onboard the Hubble Space Telescope – Advanced Camera for Surveys (ACS), Wide-Field/Planetary Camera 2(WFPC2) and Near Infrared Camera and Multi Objects Spectrograph (NICMOS) – and two ground based telescopes – the Wide Field Imager (WFI) at the ESO/MPI 2.2 m telescope at La Silla observatory and Infrared Side Port Imager (ISPI) at the CTIO/Blanco 4 m telescope in Cerro Tololo. These observations were made because it would enable us to produce a master catalogue of all the stars in the Orion Nebula Cluster. This catalogue will help answer some fundamental questions about star formation (as the ONC is a active star formation region), such as the calibration of pre-main sequence evolutionary tracks, variation of initial mass function in different environments and evolution of mass accretion rates. By talking to Carlo (the very patient PhD student who probably answers 100-200 questions a day for me) and Nicola (the post-doc), I have come to learn a lot about pre-main sequence stars, a population I have spared less thought about (until now) than the main-sequence stars, post-main sequence stars and protostars. I would like to jump into the Physics of this, but the catalogues need to be done before we can get to that.
As I have mentioned above, there are 6 catalogues – one catalogue for each camera, and one master catalogue. The cameras onboard HST have small chips so the complete cluster is a mosaic of many images taken by the cameras – and sometimes, each camera picks up the same star several times, and so one star ends up having several entries in one catalogue. Since work on these catalogues have been going on for several years (since 2006…), many of these stars have already been recognized as the same source by matching their relative RA and DEC and spectral energy distribution, but the work is not complete. Also, after recognizing these cases, they have to cross-referenced to the detections by the other cameras. The master catalogue holds all the cross-referencing details.
I am grateful for the work my predecessors (3 or 4 summer students) did before me on identifying and cross-referencing the sources, but it came at a small price – to make the final output (the atlas), people kept adding to this one master code that has now become a 2000 line monster code that badly needs simplification (which is a good training for me) and debugging. Lot and lot of debugging. I didn’t have much experience working with databases in IDL before, but I have become quite used to them in the last two weeks (again, thanks to Carlo for his patience). One thing that is really coming in handy from Observational Astronomy is the project we did with data structures. Nobody seems to have any experience with them and some are quite scared of them, so I have been a little on my own while working with them. Looking at my old observational codes have been very helpful. Some things I have tried are – opening a database once and putting all the data in a data structure instead of opening the databases every time a variable is needed. This saves a lot of time, especially for such a long code. I have also learned a few new tricks, like cutting a .fits file and reading in just a small portion of it instead of the whole image using readfits, rotating images by reading in the orientation of a camera from the header etc.
I would like to talk about the talks I have been to (about Hubble Legacy archive, hot stuff in cool stars , galaxy mergers – cool tidal tails and a 30 year old simulation by the Toomre brothers etc) but I am making this entry too long, I hope to post again soon and talk about my experience here. Take care everyone and clear skies (my Bulgarian roommate told me that’s the traditional Bulgarian greeting between astronomers)!