Background
It is challenging for MOSFIRE observers to acquire standard star
spectra that cover the entire wavelength range accessible at the H
and K passbands. A standard longslit in the center of the mask
will not necessarily cover the full wavelength range applicable to
slits at the edges of the field of view. To deal with this
problem, we have developed:
- a custom CSU mask with two slits that are offset from the
field center, and
- a script designed to acquire spectra of a standard star in
each of these two slits
As of Aug 2015, the MOSFIRE DRP does reduce
the long2pos mask observations.
long2pos Slitmask
The long2pos slitmask consists of two 3-segment
longslits for spectroscopy, plus a center alignment box for
acquisition. The mask pattern is depicted in the image below and
includes three slits:
- (at left) samples the higher wavelength range
- (in center) is for target alignment only
- (at right) samples the lower wavelength range
Options
There are two options for gathering spectra with the mask:
- long2pos: Longslit-only mode:
- Acquire 2 spectra in slit A (0.7 arcsec slitwidth)
- Acquire 2 spectra in slit C (0.7 arcsec slitwidth)
- long2pos_specphot: Longslit plus wide-slit mode:
- Acquire 1 spectrum in center of slit A (4 arcsec slitwidth)
- Acquire 2 spectra in top and bottom slit A (0.7 arcsec slitwidth)
- Acquire 1 spectrum in center of slit C (4 arcsec slitwidth)
- Acquire 2 spectra in top and bottom slit C (0.7 arcsec slitwidth)
The procedures are similar and are described below.
Procedure
Follow these steps to acquire the data:
Preliminary Steps
- Install the slitmask into the CSUMasks sub directory using
the pull down option:
MOSFIRE Utilities -> Spectrophotometric Observations ->
Install long2pos CSU mask files
- For longslit only: load the long2pos mask into MAGMA.
- For longslit & Spectrophotometric data: load
the long2pos_specphot mask into MAGMA.
Observing Steps
- Configure CSU
- Select either long2pos or the long2pos_specphot mask
- Click Setup Science Mask (not alignment mask!)
- Click Execute Mask to configure CSU
- Acquire Target
- Select the Bright Long
tab on the Slitmask Alignment Tool
- Have OA acquire star with guider and send to SLIT
pointing origin
- Click Pre-config filter to set filter and
grating to nb1061-imaging.
- Click Acquire image
- Wait for exposure to display on SAT. The red + marks
the center of the object and the yellow X marks the slit
center.
- If the object center is incorrect, click on the center
to move the red + to the correct location
- Click Move to Center to offset telescope
- Repeat previous 4 steps until object is centered
- Configure MOSFIRE
- On the Observing Mode subpanel, select the
appropriate spectroscopy mode
- Optionally, on the Exposure Control subpanel, enter the
desired datataking parameters for:
- integration time
- coadds
- sampling mode (2 for CDS, 3 for MCDS,
4 for UTR)
- number of reads
and click APPLY instead of GO. Note that
this step is optional because the automatic acquisition
script for long2pos (see step 5 below) will prompt you to enter
the exposure configuration with defaults set to whichever
values you currently have in the Exposure Control
subpanel.
- Coordinate with the OA
-
If no guide star is avaliable in the MOSFIRE guider detector
within the blue-shaded region shown in the following figure
(e.g. star surrounded by a red circle), ask the OA to stop
guiding.
Note that the standard can be observed without guiding because
the four exposures taken by the long2pos script occur in a very
short timescale.
- Acquire spectra:
-
Note the spectrophotometric mask version will acquire spectra
in the narrow and wide slits while the long2pos mask only uses
the narrow slits.
- Launch the datataking script from the background menu
via
MOSFIRE Utilities > Spectrophotometric Observations > Acquire spectra with long2pos mask