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T.I.R.GO. --- Telescopio InfraRosso del GOrnergrat
Centro per l'Astronomia Infrarossa
e lo Studio del Mezzo Interstellare
GENERAL INFORMATION FOR VISITING ASTRONOMERS
1. THE ASTRONOMICAL STATION GORNERGRAT NORDTURM
1.1 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. 45 ffi 59 0 04 00 N,
Long. 7 ffi 47 0 30 00 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'Universit` a di Firenze''.
1.2 How to arrive
Access to the Station is possible all year round via the Zermatt­Gornergrat (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 Brig­Visp­
Zermatt (BVZ) railway. Cars are forbidden in Zermatt, and must be parked in T¨asch, 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 Milan­Brig­Gen`eve (Simplon pass via Domodossola). The Gen`eve
airport is appropriate when arriving by air as frequent trains stop in Visp, whence the BVZ can be taken
for Zermatt.
1.3 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.
1.4 Useful addresses
Centro per l'Astronomia Infrarossa e lo Studio del Mezzo Interstellare
Largo E. Fermi 5 -- I­50125 FIRENZE (Italy)
Tel. +39 55 27521 FAX +39 55 220039
TIRGO Observatory, Stazione Astronomica Nord
Kulm Hotel, Gornergrat -- CH­3920 Zermatt (Switzerland)
Tel. +41 28 671219 FAX +41 28 674850
Kulm Hotel, Gornergrat -- CH­3920 Zermatt (Switzerland)
Tel. +41 28 672219 FAX +41 28 672286
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2. THE T.I.R.GO. TELESCOPE
2.1 Telescope and mount
The TIRGO telescope is a Cassegrain telescope with a wobbling secondary and optimized for infrared ob­
servations. 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 field­of­view
(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 worm­gear 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 – 015 ffi .
The TIRGO Observatory is described in Salinari (1982).
2.2 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).
2.3 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 non­sidereal
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.. Autoguiding can be also performed, by
processing digital images provided by the Arlunya module (see Section 2.8). The telescope control system is
described in Agnoletti et al. (1991).
2.4 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.
2.5 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 ffi 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.
2.6 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 2 2:4 arcmin with the focal
reducer, and 1:7 2 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).
2

2.7 Finder
A small refractor equipped with an astronomical grade CCD is mounted on the telescope structure. The
image size is 165 2 192 pixels, while the FOV is 6:5 2 6:5 arcmin. The finder is equipped with a series of
colored filters, with the red filter being the most sensitive. The limiting magnitude is lower than that of the
Bosch, and is around 10.0 mag in dark time.
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 fixed­time 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.
3. INSTRUMENTS
3.1 TIRGO Near­Infrared (NIR) Photometer (FIRT)
The TIRGO NIR photometer uses a single InSb detector with cooled low­noise amplification electronics.
Detector, filters, and diaphragms are cryogenically cooled to solid nitrogen temperature. FIRT is controlled
through a PC interface and a C­language data acquisition system with pull­down 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 broad­band NIR observations
are background­limited, will vary with observing aperture. FIRT gives the following choice of filters and
diaphragms:
Filters
Name – [¯m] 1– [¯m] Diam. [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 a 34
D6 a 41
a only with H(large) filter
FIRT limiting magnitudes
Band Limit a Sky Magnitude [mag arcsec 02 ]
J 13.5 13--14
H 13.1 13.5
K 13.2 12.5
L 8.5 3
M 5.5 0
a 10oe in 15 min. with 28 arcsec diaphragm.
3

3.2 Gornergrat Spectrometer (GOSPEC)
The TIRGO NIR spectrometer uses seven adjacent InSb detectors with the same low­noise amplification
electronics as the photometer. The detectors are cryogenically cooled to solid nitrogen temperature, while
gratings, filters, and diaphragms are cooled to liquid nitrogen. GOSPEC is controlled through a PC interface
and a FORTRAN­language data acquisition system with a command­language parser. The instrument is
described in Lisi et al. (1990) and the software in Morbidelli (1994).
GOSPEC sensitivity and limiting magnitudes
– Order Resolv. Efficiency Limiting Sensitivity
[¯m] Power [%] magnitude a
10 018 W m 02 10 014 W m 02 ¯m 01
1.25 2 660 0.8 10.8 300 16.0
3 1120 5.8 12.5 33 3.0
1.65 1 420 2.6 10.2 67 1.7
2 940 11.0 12.8 16 0.9
2.20 1 570 10.0 12.7 12 0.3
2 1460 8.0 11.4 16 1.1
3.80 1 1150 3.0 8.0 106 3.2
4.60 1 1900 2.0 6.5 140 5.7
a Magnitudes and sensitivities in J, H, and K bands are at S/N = 1 and are based on an estimate of the total
noise of about 25 e 0 in 600 s of integration time (elementary integration time 16 s) with the 1.5 m TIRGO
telescope. In L and M bands, the limiting noise is the background fluctuation; the quoted sensitivities are
for S/N = 1.
3.3 The ARcetri Near Infrared CAmera (ARNICA)
ARNICA is the Arcetri imaging camera for the near­infrared bands between 1.0 and 2.5 ¯m. It relies on
a Rockwell HgTeCd array detector NICMOS 3 with a 256 2 256 pixels format (40 ¯m pixel size); at the
TIRGO 1 pixel corresponds to 1 arcsec, which provides a FOV of more than 4 arcmin24 arcmin.
NICMOS 3 array detector performance
Format 256 2 256
Bad pixel 0.5%
Peak quantum efficiency (2.2 ¯m) ú 0:65
Well capacity 2:4 2 10 5 e
Dark current (76 K) 0.5 e s 01
Read noise 45 e
The quoted well capacity is the level at which the non­linearity 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 1­inch filters
in the current implementation. Besides the standard set of astronomical filters for the J, H, K bands,
presently mounted are four narrow­band filters for collecting images in selected spectral lines (He I 1.083¯,
[Fe II] 1.644¯, H 2 2.122¯ and Brfl); their average bandwidth is ¸1%, while their average transparency is
¸60%. With narrow­band 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 fiber­optics link. A C­language
package, running under MS­DOS 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.
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Typical performance of ARNICA at TIRGO
J H K
Background 1:5 0 3 2 10 3 8 0 10 2 10 3 4 0 7 2 10 3
(e s 01 arcsec 02 )
Efficiency 0.15 0.29 0.30
(e/photons)
Background 14.5--15.5 12.5--13.5 13.0--13.5
(mag arcsec 02 )
Limiting magnitude 19.3--19.7 18.5--18.6 18.3--18.5
(arcsec 02 , 3oe, 60 s)
Limiting magnitude 18.2--18.6 17.4--17.5 17.2--17.4
(3 arcsec FWHM, 3oe, 60 s)
The values in the table take into account the flat­fielding process, and assume background­limited perfor­
mance; the assumption of background­limited performance has been verified experimentally. When suitable
observing techniques are used, the flat­fielding 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 single­detector photometer. The characterization of the detector and the broad­band performance of
the camera are described in Hunt et al. (1994a, 1994b). Suggestions for broad­band image acquisition and
data reduction are given in Hunt et al. (1994c).
3.4 TIRGO Optical Photometer
The TIRGO optical photometer, constructed by the ``Istituto di Fisica dello Spazio Interplanetario'' (I.F.S.I.),
uses an EMI 9893B/350 phototube together with a set of U, B, V Schott filters. The system also includes
a set of neutral filters. A description of the photometer is given in Baldetti et al. (1987), and preliminary
results give a limiting V­magnitude of ¸16. The TIRGO optical filter system closely approximates the
Johnson system. The following filters and diaphragms are available with the optical photometer:
Filters
Name – [nm] 1– [nm]
U 355.0 70.0
B 445.0 90.0
V 545.0 80.0
Diaphragms
Position Diam. [mm] Diam. [arcsec]
1 0.97 6.66
2 1.49 10.20
3 2.25 15.45
4 3.37 23.15
5 5.42 37.20
6 8.99 61.76
7 15.31 105.00
8 25.60 175.77
5

4. COMPUTER SYSTEM
The telescope and instruments are independently run by four 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.
4.1 Telescope control system
The computer assigned to telescope control is an industrial grade VEGAS 3625, a 386DX PC with a 40
MHz clock (8Mb RAM), equipped with a 80387 coprocessor and a 170 Mb hard disk. The VEGAS commu­
nicates 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.
4.2 Data acquisition system
The computer assigned to data acquisition from FIRT and GOSPEC 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 00 ),
720 Kb and 1.44 Mb (3:5 00 ). All observers should bring from their home institution the necessary diskettes,
previously formatted on their home computer. Diskettes (either formatted or unformatted) will not be
supplied by the Observatory.
Two printers connected to the parallel ports of the data acquisition computer are also available for use;
one (Digital) is used primarily for plots of spectroscopic data and the other (NEC) is used for printing data
files.
When the computer is switched on, the available options include: 1) FIRT data acquisition; 2) FIRT
test; 3) GOSPEC data acquisition; 4) GOSPEC test; 5) Park hard disk before turning off PC; 6) Format
disk in drive A; 7) Format disk in drive B. Options 1 and 3 are described in Arcetri Technical Reports (Baffa
1992; Morbidelli 1994). 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 multi­tasking
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 00 ), and the other with density up to 2.88 Mb (3:5 00 ).
The DAT unit connected to the SUN workstation can be used for data storage and transfer; observers should
bring the DAT cassettes they need from their home institute as they are not available on the mountain.
4.3 Data reduction system
In the small study, a SUN workstation and an Amstrad PC­AT 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. If any of the existing files are changed (e.g.,
AUTOEXEC.BAT, for the PC), they should be restored to their original state. 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 Amstrad include FRAMEWORK II, TeX, LaTeX, Windows, Nautical Almanac, Kermit, vi,
and qedit, grep, and other Unix utilities.
The workstation is a SUN 4/110, with a 32 Mb RAM and a 2 Gb hard disk, about 600 Mb of which are
available to users for data reduction: a local account named tirgo is available for public use. Peripherals of
the SUN station 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. IRAF and the ARNICA reduction package is available
for image reduction.
6

4.4 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. on­line) and can be imported into PC programs such
as FRAMEWORK, LOTUS­123, MATLAB, etc.. The photometric data reduction is easily performed in
any of these environments.
Spectroscopic data from GOSPEC can be reduced by importing the FITS files into any image reduction
system (e.g., MIDAS or IRAF), or by importing the ASCII files into one of the above­mentioned PC programs.
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).
4.5 Network connections
The SUN station is connected to Internet network, and a local Ethernet network connects the SUN with the
PCs in the control room. A 1200­baud modem connection is also available, but its use must be limited to
emergency cases.
5. 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 strip­chart 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 static­proof, 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.
6. CRYOGENIC SYSTEM
6.1 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.
6.2 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.
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6.3 Instrument cryogenics
In both InSb instruments (FIRT and GOSPEC), the external chambers must be filled twice daily; replenishing
the nitrogen in the internal chambers is typically performed every five­six days by authorized personnel.
Regeneration of the active carbon in GOSPEC is also carried out during the replenishment of the GOSPEC
internal chamber. Internal chamber temperatures are typically 55­60 K and correspond to PT100 readings
of 10--13 (FIRT) or 7--8 (GOSPEC); the remaining two PT100s in GOSPEC measure the external chamber
temperature (liquid N 2 ) and should be in the range 20--22. 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 dewars; two rotary pumps are used for
cryogenic pumping of the internal chambers.
7. SUPPORT SERVICES
7.1 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.
7.2 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.
7.3 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 tirgo@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.
7.4 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.
7.5 ``Good­conduct'' 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.
8

8. GUIDELINES FOR OBSERVERS
8.1 Observing proposals
For submitting proposals one must use the standard application form that is attached to the Call for Proposals
regularly sent to interested parties. A TeX version of it together with instructions for compilation, regularly
sent via E­mail to a list of observers, can be also found in the tirgo@arcetri.astro.it public account.
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.
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.
8.2 Pre­observation bureaucracy
Approved investigators will receive a letter with the scheduled time for observations, together with general
information. Soon thereafter, they should provide the Center with the name(s) of the observer(s) as well as
expected arrival and departure times. They should also specify if they need special assistance.
Observers may also contact the Center for general information about logistic and travel arrangements
(e.g. local train connections). Especially during high season, reservations should be made well in advance.
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.
Observers belonging to Italian public institutions may also ask for a per diem and for travel expenses
reimbursement. However the Center will not pay more than one observer per run, and only if the request
(RICHIESTA DI MISSIONE), compiled in detail and signed, arrives at least 2 weeks before the beginning
of observations.
The request must be accompanied by an authorization (AUTORIZZAZIONE A RECARSI IN MIS­
SIONE ALL'ESTERO) which indicates the place (Gornergrat, Switzerland) and the observation period. We
notice that, while an authorization for a period longer than the effective one is allowed, one for a period
shorter than that would create serious bureaucratic problems. This authorization must be signed by the
Director of the observer's home institution, namely by 1) the Director of the Department for University
researchers or fellows; 2) the Director of the home observatory, for astronomers; 3) the Director of C.N.R.,
or local equivalent, for C.N.R. researchers.
Usually only a 2­way train ticket (shortest route from the home institution to TIRGO) is reimbursed.
Different solutions require an explicit justification and authorization by the Director of the observer's home
institution. Moreover only one 2­way ticket for the GGB is normally reimbursed. More such tickets are
reimbursed only if accompanied by a signed justification that additional tickets were needed for duty reasons.
Observers wishing to use their own instruments should also indicate in detail the weight and encumbrance
of their equipment, as well as the technical support required from the Center.
8.3 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 00
diskette.
We strongly encourage guest observers to format data diskettes (either 5:25 00 or 3:5 00 ) on their home
computer. Estimate about 200--300 Kb per night with FIRT, and 500--1000 Kb per night with GOSPEC. Note
that GOSPEC output can be obtained either in FITS format or ASCII, so that additional diskettes should
be prepared if both forms of data are desired. Estimate about 300--400 images per night with ARNICA, for
a total of 60--100 Mb. A typical run should easily fit on a single DAT tape.
9

8.4 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 non­routine tests
or for observations of exceptional transitory phenomena (supernovae, outbursts, etc.).
8.5 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).
Because of the variety of spectroscopic observational exigencies, calibration stars for GOSPEC are not
provided and are left to the discretion of the observer. An analysis of GOSPEC performance together with
observing guidelines are given in Hunt et al. (1991).
A glance at the bulletin board situated in the control room is advisable. Recent software changes,
troubleshooting hints, and other potentially useful information no