REM:: Observing

REM programmed observations.

Please find in the programmes page the list of forthcoming REM observations.

REM observing modes

REM is a small size telescope (60cm diameter) and although with quite advanced technological solutions any observing program should be well fitted within the instrument capabilities. Plase look at more detailed informations concerning observing time request and allocation.

REM allows simultaneous optical (0.5 - 0.8 micron) and near-infrared (1.0 - 2.2 micron) observations automatically managed with fast pointing capability everywhere above 5 degrees on the local horizon.

Below there are the possible observing modes offered by the observatory:

  1. RRO Rapid Response Observation. REM is permanently liked to the GCN and IBAS networks to receive alerts from the Swift, Integral and Hete-2 satellites. Each time an alert is received REM stops any possible on-going observation and immediately goes to the new target beginning a sequence of pre-defined observations. Data for GRB alerts are property of the REM team, other high-energy transient data can be accessed upon an agreement with the REM team. It is possible to add new source of alerts but since this requires a modification of the REM Observing Software (REMOS) this has to be discussed with the REM team.
  2. RTOO Regular Target of Opportunity Observation. This mode is offered to general users. Through an e-mail to a dedicated address ( the staff will allocate the observation soon as possible (usually few hours after). REM system will execute the observation as soon as it's night.
  3. PM Periodical Monitoring. Observations can be requested for any target and with this mode the observations are performed periodically. This is not intended as a mode for precise timing (see below). Periodical monitoring means that the next observation is not executed before a specific amount of time (the periodicity).
  4. TO Timing Observations. It is possible to introduce in the system observations performed within a strict time-window for accurate synchronization.
  5. OSO One-Shot Observation. The simplest observation mode. The requested observations are allocated when the observability conditions are the best.

For each observing mode, excluding RRO, it is always possible to set constraints about the airmass, seeing, Moon distance, etc. It is also possible to group different observations together in order they are executed during the same night sequentially.
REM routinely observes (i.e. almost each night) standard stars available for each program. It is of course always possible to allocate standard stars for specific needs.

REM observation priority

(added March 2021)

In case of conflicting request for time constraint observations, priority will be given to the first activation from an approved program.

REM observation block

The observing block logic

A REM observation block (OB) is the configuration of the telescope and the ROS2 and REMIR instruments, plus other parameters useful for the night schedule computation.

The OB parameters can be divided into the following parts:

The REM scheduler checks the visibility of the target, the observation constraints (the time constraints, it they are set), group option, and builds a night list of elementary observation block (EOB) with guessed start and end epochs. 

Following the computed time order, the scheduler sends the elementary operations to the telescope system (TCS) and to the cameras (both, if required). 

The elementary operations means coordinates for the TCS; exposure time and integrations number for ROS2 camera; DIT, dither cycles number and IR filter for REMIR camera (figure 1).

When the TCS is in tracking status, the cameras start the exposition(s). REM will be ready for another elementary operation when the cameras (both) send an "end operations" to the system.

Figure 1
The REM scheduler logic. In this diagram the REM OB archive box represents both the OBs database and the temporary OBs list in the REM system.

As REM accepts configurations requiring simultaneous observations with both instruments and multi-filter observations (REMIR), an OB can contain multiple EOBs (figure 2).

Note: the EOB DIT values are the same for each filter. 

The scheduler runs each EOB of an OB in sequence. The OB will end when all EOBs are concluded (figure 2). If an error occurs, the EOB will be redone. Every time that an OB ends, then REM scheduler re-computes a new night schedule (some changes in the schedule can occur, e.g. if there are errors, TOO, GRBs, OBs with time constraints, etc.). 

The non-periodical OBs will be marked as done, and deleted from the REM archive. Periodical OBs remain in the archive and will be put back in the schedule at the given rate (e.g. after a data time ≥ period set).

Figure 2
The elementary observation block (EOB) vs. the observation block (OB). Each EOB keeps the same configuration of the telescope (TCS), while it changes the REMIR configuration. The ROS2 configuration remains constant in all EOBs.

Object parameters

Object parameters provides to the telescope the target data and are the following: The category parameter is useful and required for the database query. The following categories are provided: The M2 defocus parameter can be set when the target is bright. The telescope system will perform a defocus starting from the computed focus position (based on the temperature of dome, telescope mirrors) and applying the required offset.

The infrared camera parameters

The REMIR parameters defines the REMIR camera setup and are the following: If the OB has IR flag true, then the REMIR camera is activated for the observation. 

REMIR uses a dither 5 positions in a pentagon shape with a sides of about 30 arcsec, thus for every observation carried provides 5 dithered images.

If the OB mode is set in multi-filter mode (JH, JK, HK, JHK), the REM scheduler splits the OB into EOBs, one for filter. 

In this case REMIR runs a complete dither cycle for each filter following the EOBs order in the schedule (usually the order is J, H and K). 

If NINT parameter is < 1, REMIR runs a multiple dither cycles. In this case the sequence is NINT dither cycles in the first filter, NINT dither cycles in the second filter, etc. 

For example: NINT = 3 and IR Filters JH, the sequence will be JJJ HHH.

For extended objects or for a better sky subtraction we suggest to activate also the jitter setup.

The optical camera parameters

The optical camera parameters defines the ROS2 camera setup and are the following: If the OB has Optical flag true, then the ROS2 camera is activated for the observation.

ROS2 is a multi-filter camera, thus the exposure time is the same for all 4 channel (g', r', i' and z').

It's possible to set the CCD for a gain of 1.0 e-/ADU or 4.4 e-/ADU.

The collimator position parameter sets the position of the ROS2 camera collimator applying the given offset value.

The observation constraints

There are 2 observation constraints parameters: These parameters are used by REM Scheduler to build the night schedula, e.g. setting the start observation for the OB when the airmass is less than Max Aimass parameter, or not put in the schedula the OB when the Moon faction is greater than Max Moon Fraction parameter.

The default values are the most permissive (Max Moon Fraction = 1.0, Max Airmass = 5.).

OB periodicity (PM mode)

These parameters mark the OB as periodical, thus REM Scheduler will not delete the OB from REM temporary archive (the OB will be not put in the night schedule if it's not visible during the night).
The parameters are the following: If the OB has Periodical flag true, REM scheduler puts the OB in the night schedule only if the elapsed time since the last performed observation is greater than Periodicity days.

It's possible for particular reason to extend the maximum value over 30 days, otherwise we suggest to duplicate the OB and eventually set a Time Constraints.

Time constraints (TO mode)

The time constraints are used by the REM scheduler to define the start (and/or end) epochs of the observation of an OB. The parameters are the following: These parameters are useful for guaranteeing a simultaneous observation with another facility.
The time span must be at least 2 times greater than the OB duration (exposures plus overheads).

Hint: the time constraints is also useful to have more than one observation per night. For example to observe 3 times a night it is sufficient to build 3 OBs with 3 different time intervals:

  1. 20XX-XX-XX 00:00:00 - 20XX-XX-XX 01:00:00
  2. 20XX-XX-XX 03:00:00 - 20XX-XX-XX 04:00:00
  3. 20XX-XX-XX 06:00:00 - 20XX-XX-XX 07:00:00
where 20XX-XX-XX represents the same date

If the OBs that are both periodical and time constrainting, the OB will be duplicated with the time constraints date shifted for the Periodicity days, while the time constraints timetable remains the same.

The jitter parameters

In the case of an extended objects or anytime one needs a safer sky subtraction a jitter setup can be activated.
In this case, the jitter parameters provide values to REM system to performs a jitter sequence. The parameters are the following: If the flag is true jitter, REM scheduler duplicates the OB number Nsky times where the first position are at the coordinates provided, from the second onwards REM calculates a position R.A. and Dec randomly inside the frame with the inner side value = Min Box and outer side = Max Box (figure 3, the jittered coordinates are chosen inside the gray part).

Since OB is duplicated, the whole setup is repeated as a different grouped OB (REM scheduler add at the end of the object name the flag '_s').

An example can be the following configuration (figure 3):
DIT = 10, NINT = 2, Filter = JHK, Nsky = 3
the sequence will be:

  1. JJ HH KK in the first position (target coordinates provided)
  2. JJ HH KK in a first jittered position randomly calculated inside the frame (gray region)
  3. JJ HH KK in a second jittered position randomly calculated inside the frame (gray region)

Note: if the ROS2 flag is true, the optical observations will be performed also in the jittered position.

Figure 3

The group of OBs parameter

The group parameter marks all OBs with the same group value as a sequence to be executed during the same night.

The REM scheduler then tries to put in the night schedule sequentially all the grouped OBs, but there is the still the possibility that REM will not observe sequentially the OBs (or worse not in the same night) if the whole group cannot be fit easily.

The group parameter identificator is a positive integer (not 0).

This possibility is also useful when it's required a different DIT value for REMIR filter, or different configuration for the same object (e.g. deep exposure + short exposure).