NOTcam WFC spectroscopy: Z-band spectroscopy

Commissioning of the spectroscopic mode of NOTcam was finalised in 2005.
Low-res spectroscopic J, H, and K-band first-light observations were obtained in August 2003.

In March 2004, Dr. Groeningsson and Dr. Mattila from Stockholm University obtained the first spectra with NOTcam's Y_n-band filter (ID #222). This narrow filter samples 1.00 to 1.06 microns, approximately: this filter transmission bares no resemblance to that of the much wider standard Z filter, as defined for optical CCDs.

Stellar spectrum obtained with the Wide Field Camera and the Y_n filter. The 6th order runs from the Y_n cut-off around 1.06 micron towards shorter wavelength at the top of the image. The 7th order runs from the bottom of the image to the Y_n cut-on at around 1.0 micron. The two orders overlap in wavelength. In this 200 second exposure no clear sky-lines are visible, implying that proper wavelength calibration awaits a dedicated calibration unit (as for the J-band spectra).

Spectrum extracted from the image shown above, showing the flux distribution along the chip.

Comparison to ALFOSC

The plot shows the ALFOSC+CCD#8 counts in e-/s/Angstrom using grism #5, and the NOTCAM counts using the only spectroscopic setup that we have (grism #1). The same star was used but on different nights, so the results may depend on this a little but are according to expectations.

The ALFOSC spectrum cuts at about 10250 Angstrom due to the end of the chip. The ALFOSC spectrum is plagued by fringing.

The NOTCAM counts are drawn with 2 dotted lines, showing the contribution of grism order 6 and 7. The NOTCAM filter used is the Y_n filter (ID #222, or 1 micron filter), which is the 'bluest' 'wide-band' filter we currently have in NOTCAM.

The implications of these data is that NOTCAM gives better throughput than ALFOSC down to at least as blue as 9300 or so, and with much less fringing effects. Currently we are not able to benefit from these NOTCAM features as we dont have appropriate wide-band filters for imaging and spectroscopy, nor a NIR grism that is optimised for this region.

John Telting (jht)