The McDonald
Large Cassegrain Spectrograph is a long slit low-moderate (R~600-2500)
resolution CCD spectrograph optimized for the spectral range 0.3-1
micron. The instrument is used on the Harlan
Smith 2.7m telescope at the f/18 Cassegrain focus.
The instrument
is attached to the Automated Telescope Offset Guider (ATOG) module
at that focus, which provides acquisition and guiding capabilities,
as well as calibration lamp illumination. The LCS offers on-axis
guiding off the slit jaws, as well as off axis guiding options.
This page provides basic information for proposal development.
New observers
will want to consult the latest versions of the LCS/ATOG User Manual (pdf) for detailed instructions, and the 2.7m Telescope Control System Users Manual before starting an observing run. The LCS/ATOG ICE commands are documented here. See also the McDonald Observatory Observer Information page. On the Request for Services form, available at
this page, LCS observers must specify needed gratings, filters,
and CCD.
Contacts: (e-mail
@astro.as.utexas.edu)
| Scientist: |
Anita Cochran
(anita) |
512-471-1471 |
| Observatory Support: |
David Doss
(doss) |
915-426-4111 |
|
LCS Observing Options:
| Slit: |
Width remotely
continuously adjustable (bilaterally) from 0.8" to 15". |
| Decker: |
Remotely selectable
between two options : 80" long and 250" long. |
 |
The
location of the slit and decker on the science array is remotely
adjustable. |
|
The
orientation of the science CCD array with respect to the slit
can be adjusted manually at the telescope,
if necessary. |
|
The
position angle of the slit on the sky can be adjusted manually
at the telescope by rotation of the entire ATOG/LCS. Nominal
default orientation of the slit is EW (PA=90). |
|
|
| Filters: |
Located
below the slit are two filter wheels. These can be used in any
combination to isolate grating orders. Default filter set is
given below. |
 |
The
CuSO4 filter may not be installed. Be sure to specify if you
need it. |
|
Wheel #1 has five
locations. Wheel #2 has eight locations. |
|
|
| CCDs: |
Two
science CCDs are available for LCS. TI1 chip has higher overall
QE. |
McDonald CCD Arrays available for LCS
| device
name |
device
type |
format |
pixels |
plate
scale
(no binning) |
| TI1 |
thinned, back-illuminated
Texas Instruments |
800x800 |
15.2µm |
0.64"/pix |
| CC1 |
unthinned, front-illuminated
Loral/Fairchild |
1024x1024 |
12µm |
0.51"/pix |
|
|
The
TI1 chip has serious fringing at >6500Å. Flat fields
should be done carefully. |
|
CCD dewar
LN2 hold time is >24 hours. |
|
|
| Gratings: |
The
LCS offers remote selectability among three gratings chosen from
those in the list below. |
Diffraction Gratings available for LCS
grating
number |
lines/mm |
blaze
(Å) |
effective
blaze (Å) |
dispersion
l/ one-pixel
Dl
(TI1 CCD) |
| 40 |
300 |
4200 |
3900 |
550 |
| 41 |
300 |
7500 |
6000 |
550 |
| 42 |
300 |
10000 |
9200 |
550 |
| 43 |
600 |
4000 |
3700 |
1100 |
| 44 |
600 |
7500 |
6900 |
1100 |
| 45 |
600 |
10000 |
9200 |
1100 |
| 46 |
1200 |
4000 |
3700 |
2200 |
| 47 |
1200 |
6000 |
5500 |
2200 |
| 48 |
1200 |
7500 |
6900 |
2200 |
|
|
Gratings
are blazed for use in first order. |
|
For CC1
array, the dispersion is 15/12 that of TI1 (ratio of pixel pitch). |
|
Note that there
is considerable flexure in the grating holder. Once a grating
is set up to the desired tilt, the assembly should be manually
clamped to ensure wavelength stability. |
|
Grating tilt drive
cannot reach >7500Å for gratings 47 and 48. These gratings
must be mounted in the rightmost grating slot, and therefore
cannot be used together. |
|
|
| Calibration
Lamps: |
Three
calibration lamps are mounted within the ATOG and above the LCS
and are usable remotely for calibration. Argon and neon can be
used in situ without moving the telescope. |
Calibration Lamps available for LCS
| lamp
name |
lamp
type and location |
| argon |
hollow cathode argon lamp
in the ATOG above LCS |
| neon |
hollow cathode neon lamp
in the ATOG above LCS |
| incandescent |
incandescent
lamp
projected on dome
flat-field plaque |
|
|
The
hollow cathode lamps have fairly unique line ratios. It is suggested
that observers use the linked spectra tofind their way around. |
|
A flat field plaque
with UV-relfective paint, illuminated by quartz lamp, is available
on the inside of the dome for flat fielding. |
|
The calibration
lamps offer a filter wheel for attenuation. ND0.3, 0.5, 1.0,
and 2.0 filters for the lamps can be selected remotely. |
|
| Sensitivity: |
TI1 chip, grating
40, 1-pixel resolution
S/N=100 on V=17.5 B-V=0 in 3.7 hours of integration |
|
