Guidelines for service observations

1. Contact point and tutor astronomer

Each program with approved service observations has a tutor TNG astronomer (hereafter TutAst), who handles all the communication with the program P.I. or his/her delegate (hereafter HomeAst). The TutAst will contact the P.I. before the beginning of the semester.

The TutAst is in charge of helping the HomeAst in the preparation of the material needed for the observations, i.e. observing blocks, catalogues, finder charts, and any relevant information. Moreover, the TutAst is generally available to communicate about matters concerning the program, as well as data retrieval from the IA2 archive in Trieste.

2. Observing blocks

The observations of DOLORES and NICS can be organized in observing blocks (OBs) which consist of one or more exposures of a given object with a given (fixed) instrument configuration. The credentials to access the FLEX interactive web system will be sent to the P.I. through the IA2 archive. For simple programs, the FLEX system may not be needed. In this case, the HomeAst will send the relevant information, together with the corresponding catalogues and finder charts, to the TutAst.

For HARPS-N and GIANO-B, FLEX must be not used. For observations with these instruments, The HomeAst is expected to send the relevant instructions, together with the corresponding catalogues and finder charts.

Please note that the above material must be provided days in advance, to be properly checked by the TNG staff. Since several interactions are often needed, late information may not be processed in time to guarantee a correct execution of the observing program.

3. Times and overheads

Overheads must be included in the justification of the requested time. Lacking or incomplete computation of the overheads may result in a downgrading of the proposal.

The exchange between instruments within same Nasmyth focal station (i.e. DOLORES-Harps-N) usually takes about 10 minutes, while the change of Nasmyth (e.g. switching from NICS to DOLORES) may take up to about 15 minutes. After a change of instrument, re-focusing may be needed (about 15 min)

For DOLORES and NICS, the overheads can be estimated as follows:

  • Telescope pointing and guide-star acquisition: 5 minutes
  • Centering object into the slit: 5 minutes for sources which are bright (i.e. clearly visible on a 1 min image) or with well known position relative to bright object(s) in the field. Direct centering on faint sources may be very inefficient and is not recommended.
  • Change of instrumental setup (e.g. change of filter or grism with the the telescope tracking on the same object): 1 minute.

GIANO-B overheads: see the GIANO-B web page

HARPS-N overheads:

  • Telescope preset, included dome rotation: 8 min (upper limit for large, more than 180 deg., dome rotation), 2 min (typical for new pointing within a few degrees from the previous position)
  • Centering of object on the fibre, start of guiding: 1 - 2 minutes (depends by the user)
  • Readout time (included FITS headers generation): 34 seconds
  • Telescope focusing (at the beginning of the night, or if the condition are critical): 8 - 10 minutes
See the manual for further details.

4. Standard stars

The time used for standard star observations and the corresponding overheads are part of the time allocated to the proposal and must be counted in the same way as on-target observations.

5. Spectroscopic observations of faint objects (DOLORES and NICS)

Centering the object in the slit is a relatively fast operation, if the source is bright enough to be clearly visible (i.e. with a signal-to-noise ratio higher than 10) on a 60sec pre-image. Programs requiring spectroscopy of fainter targets can be executed within the above mentioned overheads only when their position relative to a nearby (ideally within less than 1 arcmin), brighter "pivot" source is known. The observations will be then performed by aligning the slit along the object-pivot line, i.e. by rotating the instrument to a pre-determined position angle, and centering the pivot source in the slit with the due Y-offset from the center. To this purpose, the HomeAst must clearly provide the value of slit position angle and Y-offset and, ideally, include them in the finding chart as in the example below.

6. Observations of moving objects

Moving targets can be observed in service mode. The HomeAst is required to send accurate ephemerides for the scheduled nights, including "sky motion" rates (arcsec/hour).