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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 stellar rotation.

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.

 

J band


J band 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 km/s.

 

Ks band


Blowup of 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
John Telting

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