From Planets to Stars to Galaxies:
Putting Things in Their Places

By Doug Mink, Smithsonian Astrophysical Observatory

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Presented at the "Jimboree" held in honor of MIT Professor James Elliot on June 17, 2010

Finding out where spectra come from

It all started with Mars. Tom McCord, Jim's predecessor at MIT took data on Mauna Kea with three different instruments during its 1973 opposition. I got to reduce the data from the newest of those, a 250 x 250 pixel vidicon spectrometer, which covered the mineralogically interesting wavelength range of 0.3 to 1.1 microns. The slit was in a 45-degree mirror, and a photograph was taken at the time of the exposure. To find out where we were looking on Mars, I projected the photograph on a map of the disk of Mars at the time of observation. I had to work out the map from first principles as there were no widely available mapping programs at the time. Due to the fact that the spectral features we were interested in observing differences in across the disk of Mars were in a wavelength range where there was lots of internal reflection within the detector, we could never get the kind of data we wanted, but the software lived on to be used with Mars spot photometry which was observed through the same kind of 45-degree mirror. For that project, I wrote software to reproject the coordinates from the orthographic projection used for the spectrograph slit and photometer apertures to a Mercator projection which would show the entire planet. To write that program, I had to delve into the MIT Map Room's library, where I found only one book which actually gave the equations I needed. The resulting coordinates went into my second published paper in 1977 (even though the work was completed in 1975).

Occultation predictions and finder charts

At first, we used predictions by other people, and I dusted off my Mars mapping program to make a program called SKYMAP which made finder charts, including scaled overlays for the Palomar Sky Survey. I wrote my first catalog access software to read the SAO catalog for these plots. Then we

Forays into Distances

The first contact I had with measuring extra-solar distances started with occultations, too. With Deane Peterson, we used lunar occultations to measure physical distances between binary stars in star clusters, a rung on the galactic distance scale.

Spacelab 2 all-sky infrared maps

When I moved up the river to work on the soon-to-be-launched Spacelab 2 Infrared Telescope, I took a tar tape of all of the software I wrote on the MIT Unix system. Originally, I was supposed to write mapping software in IRAF, but that didn't work, so in a couple of weeks, I rewrote SKYMAP and its subroutines to deal with all-sky projections for our project. For a variety of reasons, the telescope didn't work as planned, but the software and the K-band detector did, so we got a map of the galaxy out of it.

RVSAO and Redshifts: Adding Z to X and Y

After the Spacelab 2 funding ran out, I put my IRAF knowledge to work adapting several existing programs into an IRAF package for computing redshifts by either cross-correlating object spectra with template spectra or fitting emission line centers and using their wavelength shift from rest. This package has been widely used for redshift surveys of galaxies, getting the distance to interesting extragalactic objects, and studying multiple stars and exoplanets.

WCSTools: Catalogs and good coordinates for spectroscopy

In 1994, NRAO released an open-source library of astronomical map projection software used by AIPS to put uniform world coordinate system--pixel to sky direction mapping--information into the headers of images. Astronomers wanted to match optical data to radio data, but accurate world coordinate systems were absent from most ground-based data. I started out by writing a subroutine library for SAOimage to display sky coordinates as an image is browsed. A descendent of this library is now used by the widely-used ds9 image display program. Then I used some existing software from the University of Iowa and translated my image and catalog access software from Fortran into C to make a package which could fit a world coordinate system to an image by automatically matching point sources in the image to stars in any existing source catalog.

Catalog comparisons

Over the next 10 years, I developed interfaces to each new large and/or accurate start catalog as it was released. Eventually, we wanted to know how good they really were, so I fit a set of 1736 wide field images taken by Warren Brown with world coordinate systems and compared the residuals. New results for recent catalogs, the USNO UCAC3 astrometric catalogr, the Sloan Digital Sky Survey (SDSS), and the GSC 2.3, are presented here for the first time.

Redshift surveys with multi-object spectrographs

Recent activities, besides maintaining all of the software I've talked about, include working on data reduction pipelines for mutil-object and echelle spectrographs, used for spatial and temporal surveys respectively.