Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21361105c&link_type=abstract
American Astronomical Society, AAS Meeting #213, #611.05
Astronomy and Astrophysics
Astronomy
1
Scientific paper
High-resolution spectroscopy is an essential technique in the search for extra-solar earths, time variation of fundamental constants, and dark matter in the galactic halo. A problem that must be addressed in order to improve upon existing measurements is the wavelength calibration of multi-object echelle spectrographs (MOS). Precise MOS wavelength calibration is largely an unsolved problem. Optimally, calibration light should illuminate the spectrograph pupil with the same intensity distribution as a science object. This is best achieved by making the path of the calibration light and star light follow the same optical path. For a single object spectrograph, this is straightforward. The difficulty arises when hundreds of apertures (fibers) located in different places in the focal plane must be calibrated in a reasonable amount of time. The ThAr calibration lamps typically used for high-resolution spectroscopy are too faint to reflect from a dome screen that acts as a proxy for an infinite conjugate, and shining lamp light directly onto the focal plane leads to position- and fiber-dependent shifts and distortions of the wavelength scale. We present preliminary results from a scheme we have deployed at the MMT 6.5m telescope to wavelength calibrate the Hectochelle MOS with tunable lasers. Narrowband tunable lasers are bright enough to compensate dome screen attenuation, and can be scanned over a typical MOS free spectral range of 10 nm in under a minute. We record the wavelengths in each laser calibration scan with a commercial scanning Michelson interferometer, which gives a precision and accuracy of 50 m/s for each line, comparable to the photon-limited Doppler precision of a typical multi-object echelle spectrograph. In this poster, we describe the tunable laser system, compare wavelength solutions generated from the tunable laser system and ThAr lamps, and present examples of astronomical data calibrated with the laser.
Brown Shanique
Cramer Claire
Dupree Andrea K.
Korzennik Sylvain G.
Lykke Keith R.
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