NOTcam HRC med-res spectroscopy: first light
Besides the standard JHK low-res spectroscopic setup that is offered
by the Wide-Field Camera, one can also use the High-Resolution Camera
(HRC), to obtain medium-resolution spectra.
For each grism the spectral resolution is upped by a factor 3 when
using the HRC, and consequently the sampled wavelength range in each
order is a factor 3 shorter. As we currently have only 1 grism, the
medium-resolution mode currently offers rather limited wavelength
ranges in the JHK bands: 1.26-1.34 micron (Pa-beta), 1.57-1.67 micron,
2.07-2.20 micron (Br-gamma). Respective dispersions are 0.87, 1.08,
1.39 A/pix. With the dedicated 0.5 arcsec slit (approx 2.5 - 3 pixels
wide), the JHK resolutions are R=5700, 5700, 4900 respectively.
For the first-light observations of HRC medium-resolution spectroscopy
we chose the same object as for the WFC
low-res first-light observations , in order to allow direct
comparison of the results.
On the evening of May 18, 2005, we observed the bright Be star 66
Ophiuchi (B2Ve, V=4.6). Be stars are rapidly rotating main-sequence B
stars with strong recombination emission lines arising from a
quasi-keplerian circumstellar disk. The origin of the disk is under
great debate, but it is clear from abundant observations that the star
feeds the disk, i.e. these disks are the opposite of accretion disks.
Proposed mechanisms to feed the disk are non-radial pulsations,
magnetic fields and stellar wind, all in combination with rapid
We used baffle-lamp flats for flatfielding/fringe-correction. We used
the new Ar and Xe lamps, also located in the telescope baffle, for
wavelength calibration. The star was observed in an AB nodding
pattern for J, and Ks with 200 second exposure time at each
telescope position. For correction of telluric lines and fringes we
used the F4V star HIP86835 (V=6.6, one exposure of 200s for each band).
The spectra were optimally extracted.
spectrum of 66 Oph. Flat fielded/fringe corrected, bad-pix corrected,
optimally extracted, and subsequently normalised by using the
comparison star HIP86835.
Note that Paschen beta 1282.2 nm is
strongly in emmission in 66 Oph, and that contrary to the low-res (WFC) observations, the double peaked
structure is now clearly resolved with a peak separation of about 160
the Ks band spectra of 66 Oph and HIP86835. Top: extracted without
flatfielding/fringe correction. Middle: extracted using simple
flatfielding/fringe correction. Bottom: spectrum of comparison star
HIP86835 extracted using simple flatfielding/fringe correction.
Brackett gamma is strongly in emmission in 66 Oph, but the
double-peaked structure of the line profile may be affected by
imperfect fringe correction. In the uncorrected spectra peak-to-peak
fringe levels are on the order of 25%.
Last updated Sep 2005