T.I.R.GO. - Telescopio InfraRosso del GOrnergrat
Centro per l'Astronomia Infrarossa
e lo Studio del Mezzo Interstellare
GENERAL INFORMATION FOR VISITING ASTRONOMERS
The Astronomical Station Gornergrat Nordturm
Location
The Gornergrat Nord Astronomical Station which hosts the "Telescopio InfraRosso
del GOrnergrat" (T.I.R.GO.) is located on the northern tower of the Kulm
Hotel at Gornergrat (Lat. 45deg59'04" N, Long.7deg47'30" E, 3135 m altitude)
near Zermatt.
The Gornergrat Astronomical Station is one of the Scientific Stations
of the "Hochalpine Forschungsstationen Jungfraujoch und Gornergrat" (H.F.S.J.G.).
The telescope and related instrumentation is property of the Italian "Consiglio
Nazionale delle Ricerche" (C.N.R.) and is run by the "Centro per l'Astronomia
Infrarossa e lo Studio del Mezzo Interstellare" (C.A.I.S.M.I.) -- Firenze,
with the assistance of the "Osservatorio Astrofisico di Arcetri" and the
"Dipartimento di Astronomia dell'Universita' di Firenze".
How to arrive
Access to the Station is possible all year round via the Zermatt-Gornergrat
(GGB) railway. Limitations arise from the touristic character of this line
since the last connection up to Gornergrat in low season (October--November)
is considerably earlier than that at other times. Moreover, during high
season, groups with cumbersome equipment must give precedence to skiers.
The train schedules vary seasonally and should be confirmed to ensure adequate
margin for timely arrival. Zermatt can be reached through the Brig-Visp-Zermatt
(BVZ) railway. Cars are forbidden in Zermatt, and must be parked in Taesch,
about 10 km from Zermatt; in any case the use of cars is not advisable
during winter. For observers coming from Italy, Brig is easily reached
by the international route Milan-Brig-Geneve (Simplon pass via Domodossola).
The Geneve airport is appropriate when arriving by air as frequent trains
stop in Visp, whence the BVZ can be taken for Zermatt.
The Kulm Hotel
Guest astronomers may find rooms available at the Hotel. Due to the touristic
interest of the Gornergrat and the surrounding glaciers, the hotel may
be fully booked. Therefore reservations via FAX to the Kulm Hotel should
be made well in advance to ensure adequate lodging.
The T.I.R.GO. Telescope
Telescope and mount
The TIRGO telescope is a Cassegrain telescope with a wobbling secondary
and optimized for infrared observations. The primary mirror has a diameter
of 1.5 m and a focal ratio f/2.3, while the secondary is 20 cm in diameter.
The combined focal length is 30 m, corresponding to a focal ratio f/20.
The total field-of-view (FOV) is about 12 arcmin, and the scale at the
focal plane is 6.9 arcsec/mm.
The telescope has an equatorial fork mount. Hour angle and declination
movements are driven by means of a double worm-gear system and the position
is measured by means of incremental encoders on the motor axis. Electromagnetic
and hardware limit switches do not permit hour angles larger than 4 hours,
and constrain the declination to above -15 deg. The TIRGO Observatory is
described in Salinari (1982).
Secondary mirror unit
The secondary mirror position is controlled by electronics located in the
control room (closed loop). The direction of modulation in the plane of
the sky can be arbitrarily chosen with frequencies from 0 to 30 Hz, and
amplitudes from 0 to 110 arcsec. Larger amplitudes, up to about 5 arcmin,
can be obtained at frequencies smaller than 10 Hz with a trapezoidal waveform
(i.e., 10 ms rise time). The secondary mirror unit is described in Baldetti
et al. (1981) and in Lisi (1987).
Telescope control
The system is controlled by a Personal Computer (PC) interfaced with a
microprocessor (TPA), that performs various operations, among which: 1)
setting of equatorial coordinate system by means of mechanical flags and
fine adjustment on a control star; 2) selection of different velocities
for guiding and tracking at non-sidereal rates; 3) automatic control of
dome position; 4) absolute and incremental movements on both directions;
5) pointing corrections which take into account corrections for misalignment
of the polar axis, mechanical structure flexions, atmospheric refraction,
collimation errors, etc.
Dome
The dome is equipped with a vertical shutter/wind screen opening and has
been insulated to minimize thermal gradients in the dome. Dome positioning
coordinated with telescope position is automatically performed by the telescope
control system (PC + TPA) through a hardware interface (Santerno) that
drives the dome motors.
Instrument adaptor
A multiple instrument adaptor (the "cube") is located at the direct Cassegrain
focus. It allows rapid (about 1 min) switching between up to four different
detectors mounted on the lateral faces, and hosts a TV camera on the rear
face. This switching is accomplished by a system of four mirrors, that
can be set at 45 deg positions and feed the respective faces (labelled
as A, B, C, and D for South, East, North, and West directions). Mirrors
for optical instruments are partially reflecting, while those for IR instruments
are of dichroic material, and reflect only in the IR wavelength range in
order to allow the use of the TV camera also during exposures.
TV system
The Bosch intensified TV camera is equipped with a set of neutral filters
and a focal reducer which are controlled from a rack located in the control
room. The TV camera FOV is 3.4 x 2.4 arcmin with the focal reducer, and
1.7 x 1.2 arcmin directly. The limiting magnitude in dark time is about
14.0 mag without integrating, and 16.0 mag with the Arlunya image intensifier
(see Section 2.8).
Arlunya image intensifier
The Arlunya image intensifier functions as a temporal filter. The device
can be used in two modes: 1) time integration in which the current image
is the sum of the latest fixed-time integrations and is continuously refreshed;
and 2) time integration in which the current image is the result of a (typically
longer) integration, but is not updated. The only intrinsic limitation
in the device is the inability to correct for spatial variations in the
gain of the TV photocathode. Further information can be found in the Arlunya
manual in the TIRGO control room.
Instruments
TIRGO Near-Infrared (NIR) Photometer (FIRT)
The TIRGO NIR photometer uses a single InSb detector with cooled low-noise
amplification electronics. Detector, filters, and diaphragms are cryogenically
cooled to solid nitrogen temperature. FIRT is controlled through a PC interface
and a C-language data acquisition system with pull-down menus. The instrument
electronics is described in Hartill et al. (1986) and the software in Baffa
(1991, 1992). The TIRGO NIR filter system (Hunt 1986; Hunt et al. 1987;
Hunt 1991) closely approximates that of CalTech, although work is needed
to better establish a color transformation between the two systems. The
limiting magnitudes reported below are average values (roughly for a 4
mm diaphragm) and, since broad-band NIR observations are background-limited,
will vary with observing aperture. FIRT gives the following choice of filters
and diaphragms:
FILTERS
------------------------------------
Name Wavelenght Width Diam.
(mic) (mic) (arcsec)
------------------------------------
J 1.26 0.27 28
H 1.65 0.33 28
K 2.205 0.36 28
L 3.83 0.63 28
M 4.74 0.62 20
HG 1.65 0.33 42
CO 2.35 0.10 28
CVF1 1.40--2.55 14
CVF2 2.50--4.50 14
CVF3 4.40--5.60 14
------------------------------------
DIAPHRAGMS
------------------
Name Diam.
(arcsec)
------------------
D1 6.9
E1 10.3
D2 13.8
E2 17
D3 21
E3 24
D4 28
D5(*) 34
D6(*) 41
------------------
(*) only with H(large) filter
FIRT LIMITING MAGNITUDES
--------------------------------
Band Limit(*) Sky Magnitude
(mag arcsec-2)
--------------------------------
J 13.5 13-14
H 13.1 13.5
K 13.2 12.5
L 8.5 3
M 5.5 0
--------------------------------
(*) 10 sigma in 15 min. with 28" diaph.
The ARcetri Near Infrared CAmera (ARNICA)
ARNICA is the Arcetri imaging camera for the near-infrared bands between
1.0 and 2.5 mic. It relies on a Rockwell HgTeCd array detector NICMOS 3
with a 256x256 pixels format (40 mic pixel size); at the TIRGO 1 pixel
corresponds to 1 arcsec, which provides a FOV of more than 4x4 arcmin.
NICMOS 3 ARRAY DETECTOR PERFORMANCE
-----------------------------------------
Format 256x256
Bad pixel 0.5%
Peak quantum eff. (2.2 mic) 0.65
Well capacity 2.4e5 e-
Dark current (76 K) 0.5 e- sec-1
Read noise 45 e-
-----------------------------------------
The quoted well capacity is the level at which the non-linearity becomes
larger than about 1%.
The camera is cooled to liquid nitrogen temperature. Not considering
the transmission of filters, the efficiency of the optical system is better
than 80%. The filter wheel can hold a total of eight 1-inch filters in
the current implementation. Besides the standard set of astronomical filters
for the J, H, K bands, presently mounted are four narrow-band filters for
collecting images in selected spectral lines (HeI 1.083 mic, [FeII] 1.644
mic, H2 2.122 mic and BrGamma 2.166 mic. Their average bandwidth is 1%,
while their average transparency is 60%. With narrow-band filters the usable
field is circular, with a diameter of about 2 arcmin. A future implementation
will be the use of the camera also as a long slit spectrometer, based on
grisms with low or moderate resolving power.
The array control electronics is connected to the acquisition system
via a fiber-optics link. A C-language package, running under MS-DOS on
a 486~PC, allows the user to set the parameters of measurements, to acquire
images and to display them on the screen, and finally to perform a preliminary
data reduction. Images are stored on disk in FITS files.
TYPICAL PERFORMANCE OF ARNICA AT TIRGO
--------------------------------------------------------------------------
J H K
--------------------------------------------------------------------------
Background 1.5-3e3 8-10e3 4-7e3
(e- sec-1 arcsec-2)
Efficiency 0.15 0.29 0.30
(e-/photons)
Background 14.5--15.5 12.5--13.5 13.0--13.5
(mag arcsec-2)
Limiting magnitude 19.3--19.7 18.5--18.6 18.3--18.5
(arcsec-2, 3 sigma, 60 s)
Limiting magnitude 18.2--18.6 17.4--17.5 17.2--17.4
(3 arcsec FWHM, 3 sigma, 60 s)
--------------------------------------------------------------------------
The values in the table take into account the flat-fielding process, and
assume background-limited performance; the assumption of background-limited
performance has been verified experimentally. When suitable observing techniques
are used, the flat-fielding process can be precise up to a level better
than 8 parts in 10$^4$. As a consequence, the limiting sensitivity is set
by the total integration time also for very weak sources. Photometric measurements
can be attained with an accuracy of a few percent, comparable to that obtained
with a single-detector photometer. The characterization of the detector
and the broad-band performance of the camera are described in Hunt et al.
(1994a, 1994b). Suggestions for broad-band image acquisition and data reduction
are given in Hunt et al. (1994c).
Computer System
The telescope and instruments are independently run by separate PCs whose
consoles are located in the control room. Use of the data acquisition or
telescope control computer by visiting observers for data reduction, file
editing, or telecommunications is prohibited. A SUN workstation and an
additional PC are available in the smaller study for these tasks.
Telescope control system
The computer assigned to telescope control is an industrial grade VEGAS
3625, a 486DX2 PC with a 66 MHz clock and 16Mb RAM. The PC communicates
with a numerical control card, PTP 1000, through a serial interface, and
with the data acquisition computer via another serial interface. The PTP
1000 resides in a system constructed by TPA (Milano) and is responsible
for controlling the two telescope axes and the dome positioning. The system
and its software is described in Agnoletti et al. (1991). The control of
the finder is assigned to a 286 Olivetti computer.
Data acquisition system
The computer assigned to data acquisition from FIRT is a VEGAS 3625, 386
PC with a 40 MHz clock (4 Mb RAM), equipped with a 80387 coprocessor and
a 170 Mb hard disk. After data acquisition, the data files can be transferred
to floppy disks in one of the following formats: 360 Kb or 1.2 Mb (5.25"),
720 Kb and 1.44 Mb (3.5"). A NEC printer connected to the parallel port
is also available for printing data files.
When the computer is switched on, the available options include: 1)
FIRT data acquisition; 2) FIRT test; 3) Park hard disk before turning off
PC; 4) Format disk in drive A; 5) Format disk in drive B. Option 1 is described
in an Arcetri Technical Report (Baffa 199). The remaining options are the
only tasks available from the data acquisition PC. For archival reasons,
we strongly recommend that the observers communicate their name when so
requested by the data acquisition program.
ARNICA is controlled by a Gateway 2000 PC equipped with a 486DX CPU
(33 MHz clock), an 8 Mb RAM, two hard disks (220 Mb and 360 Mb, respectively).
This computer operates under the multi-tasking environment (DVX). Data
files are stored on a 400+400 Mb WORM optical disk; also available are
two floppy disk units, one with density up to 1.2 Mb (5.25"), and the other
with density up to 2.88 Mb (3.5").
Data reduction system
In the small study, a SUN workstation and a Linux PC are available for
use by staff and visitors. File editing, data reduction, and telecommunications
can be performed on both computers, although care should be taken to not
alter the contents of the hard disks. Any directories created during the
course of an observing run, as well as their contents, should be deleted
before departure. The programs available on the computes include IRAF and
MIDAS.
Peripherals include a laser printer and a DAT unit. The DAT unit is
suitable for storing large amounts of data, and may be used to transfer
ARNICA data.
Data analysis procedures
Photometric data analysis can be performed by extracting from the data
file via
grep or a similar string editor the lines that begin
with "\#" (This is described in Baffa, 1992). The result is an ASCII table
with one row for each measure (indicated by Measure No. on-line) and can
be imported into PC programs such as FRAMEWORK, LOTUS-123, MATLAB, etc..
The photometric data reduction is easily performed in any of these environments.
Data from panoramic detectors can be reduced by using either MIDAS or IRAF
packages, both available in the SUN workstation. For ARNICA, IRAF procedures
have been devised in order to automatize the reduction as much as possible
(Hunt et al. 1994c).
Network connections
A local Ethernet network connects the SUN station to the PCs in the control
room. Moreover the SUN is a node of the Internet network, with name tirgo.unibe.ch
Control Room
Control of the telescope and the instruments is effected from a control
room located on the third floor of the North Tower adjacent to the telescope;
it may be accessed from the second floor of the Kulm Hotel. The secondary
mirror, the two TV systems, the Arlunya image intensifier, and the optical
photometer hardware interface are located in two racks to the right of
the PC consoles. Also located in the control room are the two printers
connected to the data acquisition PCs; a strip-chart recorder is available
for beam profiles and should be connected to the analog output of the NIR
photometer for this purpose. Use of the various devices in the context
of NIR photometry is described in Hunt (1991). Although the floor is theoretically
static-proof, static electricity discharge can occur and should be avoided
by taking the usual precautions. We note that the electronics is very sensitive
to static discharge, and can be seriously damaged.
Cryogenic System
Production and storage of liquid nitrogen
Liquid nitrogen for use in the NIR detectors is supplied locally. A liquefier
is located in the basement; however, it can be operated only by authorized
personnel. A 300 lt reservoir of liquid nitrogen, together with a 50 lt
capacity portable dewar are located near the liquefier. Moreover, there
are at least two dewars of 25~lt capacity for maintaining a reserve of
liquid nitrogen in the dome for routine cryogenic filling of the instrument
dewars.
Liquid helium
Liquid helium is not produced locally, but can be obtained from an outside
firm. Observers who need liquid helium for their instruments are kindly
requested to inform the Center at least one month in advance. The Center
is responsible for contacting the firm, but the expenses must be reimbursed
by the observers.
Instrument cryogenics
In the photometer FIRT the external chamber must be filled twice daily;
replenishing the nitrogen in the internal chamber is typically performed
every five-six days by authorized personnel. Internal chamber temperatures
are typically 55-60 K and correspond to PT100 readings of 10--13. Both
the internal and the external chamber in ARNICA must be replenished with
liquid nitrogen twice daily. A high vacuum turbomolecular pump is employed
for ordinary preparation and maintenance of detector dewar; a rotary pump
is used for cryogenic pumping of the internal chamber.
Support Services
Lounging facilities
Bed and bath linens are available for resting and refreshing when necessary
during the night. These are located on the ground floor of the North Tower
and can be reached from the lavatory floor (basement) of the Kulm Hotel.
Canteen
A small kitchen is available for preparing afternoon snacks or refreshments
during the night; the kitchen is located on the first floor of the North
Tower (corresponds to the ground floor of the Hotel). Any foodstuffs must
be imported by the observer and are not the responsibility of the Observatory.
Study
Two studies situated on the 1.5th floor (between the first and second floor)
are available for data reduction and working. The SUN workstation and theAmstrad
PC are located in the small study and may be used for data reduction, text
or file editing, and telecommunications via Internet network with outside
computers. Daily reports as well as reports of problems encountered during
the night should be mailed, using the appropriate forms, to the Internet
address filippo@arcetri.astro.it. Also located on the study floor is the
telefax machine, whose use must be restricted to those cases for which
the computer connection is not sufficient.
Laboratories
A mechanics/electronics laboratory/workbench is located on the second floor
of the North Tower and may be reached from the first floor of the Hotel.
Use of these facilities is usually strictly limited to authorized personnel,
but in special cases they may be used by visiting observers. Permission
for use must be granted from the C.A.I.S.M.I. in Firenze. Any tools or
instruments should be used with care, and be placed, after use, where they
belong.
"Good-conduct" guidelines
Use of the canteen and lounging facilities is maintained only through the
good will and good manners of the visitors and staff. Pots, pans, dishes,
flatware, and bed/bath linens must be washed by those responsible for their
use. These services are available on a friendly basis, in order to make
observing at Gornergrat as pleasant as possible; violating the friendly
spirit means eventual closure of these facilities.
Guidelines For Observers
Observing proposals
For submitting proposals one must use the standard application form, a
TeX version of which together with instructions for compilation is regularly
sent via E-mail to a list of observers. Observers wishing to be included
in the mailing list may ask for this to the same account tirgo ,
by specifying their Internet address. Since changes in the format of application
form may arise, applicants should take care to use the most updated version,
received with the latest Call for Proposals. The relevant documentation
for application may be also copied by mosaic and/or anonymous ftp (see
Section 10). Five copies of the application form with the P.I. signature
must arrive at C.A.I.S.M.I., Firenze before the appropriate deadline.
Pre-observation bureaucracy
Named cards that allow a discount for the GGB are provided, upon request,
by the Center. Use of these cards by other than the designated individual
or for trips not strictly connected with official duties is not permitted.
The expences of the observers are no longer payed be IRA-CNR.
Preparing observations
Observers can prepare in advance a list of objects according to the format
standards given in Agnoletti et al. (1991). An ASCII copy of this list
can be imported directly into the telescope control PC via 1.2Mb 3.5" diskette.
All observers should bring from their home institution the necessary diskettes,
or DAT cassettes. Neither diskettes nor DAT cassettes will be supplied
by the Observatory. Estimate about 200--300 Kb per night with FIRT, and
about 300--400 images per night with ARNICA, for a total of 60--100 Mb.
A typical run with ARNICA should easily fit on a single DAT tape. ARNICA data
are also automatically dowloaded to Arcetri to be put into the archive.
Assistance personnel
The presence of a TIRGO staff member in the North Tower is always guaranteed
by the Observatory; however, the presence of a night assistant is not.
Upon request, observers who have never observed at the TIRGO will be provided
with an introduction to the system by an experienced staff member. Only
in exceptional circumstances will nightly assistance at the telescope be
furnished by the Observatory, and this should be arranged well in advance
of the observing run. TIRGO staff members are authorized to halt observations
when it is judged that observing conditions are compromised (either because
of weather conditions or because of technical failures). Moreover, visiting
observers must cede telescope control to TIRGO staff members when deemed
necessary for non-routine tests or for observations of exceptional transitory
phenomena (supernovae, outbursts, etc.).
Observing at TIRGO
Photometric calibration of the TIRGO filter system for FIRT is discussed
in Hunt (1986) and Hunt et al. (1987), and updated standard magnitudes
are given in Hunt (1991). The list of standard stars can be directly accessed
from the telescope control system and is found in the ASCII file tirgo.cat
.
Helpful hints for performing NIR photometry are provided in Hunt (1991).
A glance at the bulletin board situated in the control room is advisable.
Recent software changes, troubleshooting hints, and other potentially useful
information not yet formally documented may be posted. A night report on
the form provided should be transmitted daily via FAX to Firenze. Hardware
and software failures, as well as requests for material, should also be
reported via FAX, on the forms provided.
Post-observation bureaucracy
A summary of the observing run must be submitted to the Center at the end
of each campaign by sending an email to filippo@arcetri.astro.it. Timely
observing summaries help to improve observing conditions, and render the
Observatory as efficient as possible. Comments and criticisms are solicited.
Finally, the observers send to the Center a copy of any paper or congress
presentation that refers to data taken at TIRGO. PUBLICATIONS REFERRING
TO DATA TAKEN AT TIRGO SHOULD MENTION IN A FOOTNOTE ON THE FIRST PAGE "Based
on observations taken at TIRGO (Gornergrat, Switzerland). TIRGO is operated
by CAISMI-CNR Arcetri, Firenze, Italy"
Documentation
Manuals and published articles
The TIRGO Observatory is described in:
"The TIRGO Observatory", P. Salinari, 1982, Proceedings of the Second
ESO Infrared Workshop, Garching, 45 The secondary mirror unit is described
in: "Sistema di modulazione dello specchio secondario TIRGO", P. Baldetti,
F. Bordoni, A. Di Giammarco, and P. Saraceno, 1981, IFSI Internal Report
No. 81-8 and
"Il modulatore dello specchio secondario del TIRGO. Un modello del
sistema", F. Lisi, 1987, Arcetri Technical Report No. 1/87 The telescope
control system is described in:
"Descrizione del programma per il controllo del TIRGO", F. Agnoletti,
P. Cerulli-Irelli, P. Ranfagni, and M. Sozzi, 1991, IFSI Internal Report
No. 91-9 (Last Release: 4.1, dec. 1994) The TIRGO NIR photometer/spectrometer
electronics is described in:
"An InSb charge amplifier for use in a spectrometer ar