GBT Observing Policies

1. Introduction

The Green Bank Telescope is operated as a national visitor facility for qualified professional astronomers, including both expert and novice radio observers. General information on observing at the GBT and visiting Green Bank are described in the visitor information document posted at Vistor Information.

In addition to web documentation for self help (see links from Astronomers ), GBT Operations has a limited number of staff support astronomers who will aid observers in the setup and execution of their observations. In order to make most efficient use of the telescope and to conserve the time of our staff, we describe here the present practices and policies for GBT observing. Any changes and enhancements to policies, procedures, and observing facilities will be publicized through the Newsletter, our web pages, and through contact with the support staff.

2. Observing Policies

OBSERVER RESPONSIBILITIES: As a general rule, the principal investigator has the responsibility for proper supervision of all aspects of the observing program. This means, for example, that each principal investigator is responsible for obtaining all calibrations and other receiver/telescope parameters necessary for the reduction of his or her data. For this reason, we require that a qualified observer be on site to conduct observations. Apart from exceptional circumstances, we do not allow absentee or proxy (service) observing. If an observer is not able to be on site for the observations, he or she must discuss the situation with the Telescope Scheduler. In the case of student observers, the student's adviser must accompany the student for at least the first observing run on the GBT.

REMOTE OBSERVING: The GBT supports remote observing on a restricted basis. Most but not all of the required tools, procedures, and infrastructure are in place. Only those observers who have used the GBT before and have demonstrated that they are fully able to set up and observe on the GBT without staff assistance may observe remotely. Experience has shown that if an observer requires significant assistance, the process of providing this remotely is awkward to all involved, is an inefficient use of telescope time, and is overly time-consuming and taxing for our staff. Observers who are less experienced with the GBT are required to observe on site.

Observers who are sufficiently experienced and wish to observe remotely must contact the GBT Scheduler (Carl Bignell) at least two weeks in advance to request approval. The decision will be based on demonstrated experience of the observer and suitability of the program for remote execution. If permission for remote observing has been granted to a particular observer, it is required that he or she carry out the observations. The approved remote observer specifically must not pass off the responsibilities to a less experienced collaborator or student.

For approved remote observers, guidelines and suggestions for remote observing are posted at http://www.gb.nrao.edu/gbt/remoteobserving.shtml.

OBSERVER ASSISTANCE: Each observing program will be assigned a staff support astronomer ("friend") to assist in the preparations for the observing run. You will be notified of who your support friend is prior to your observing run by the Telescope Scheduler, Carl Bignell. The friend will serve as your contact person both before and after your run for all scientific and technical issues. Because of the support rotation scheme in use, a different scientist may be assisting you during your observations. This support scientist is generally available at the start of your run to assist in initial setup. This person or another scientist will be available as required during the course of the run, according to duty rotations. The friend or on-duty support scientist (or in his/her absence, the Telescope Operator) will coordinate contacting the technical or scientific staff whose assistance or expertise may be needed.

STUDENT OBSERVING: Many proposals have students who are either the P.I. or a CoI where the observations are conducted by students. To minimize the load of the very busy support staff, the first time that a student observes using the GBT, he/she must be accompanied by their supervisor (or an experienced GBT astronomer) and must carry out their first observations on site in Green Bank.

NON-STANDARD INSTRUMENTATION/SOFTWARE: Visitors who require special hardware or software configurations for their projects must make their requests at the time their proposal is submitted. Requests for non-standard facilities or capabilities will be considered in light of feasibility, priorities, project schedules, etc. Observers will be notified of the outcome when the results from the Proposal Selection Committee are distributed. Last-minute requests for non-standard capabilities cannot be granted, in general.

PROPRIETY: Observers are scheduled on the telescope with the understanding that they will pursue only the program described in their observing request. Since we have many observers from various institutions working on related programs, we require that any observers wishing to change their program (e.g., source list, observing frequencies, etc.), or to exchange time with other observers, do so only with the consent of the Site Director and Telescope Scheduler.

3. Observing Preparation

Regardless of whether observations are conducted on site or remotely, the observing will be most efficient if the observer and the support scientist work together to prepare for the run well in advance of the observations. Please make the following arrangements:

o Contact your assigned staff astronomer at least two weeks prior to your observing run. The program can be discussed, computer accounts and disk directories set up, and initial observing scripts created and reviewed. Having these scripts in place prior to the run will save much time in starting up the observing run.

o Arrive on site at least one business day in advance of your observations. This will allow observing plans to be reviewed and all last-minute preparations made. The staff astronomers can also give demos of the control and data reduction software which will save much time at the telescope.

4. Dynamic Scheduling

The GBT presently operates from ~300 MHz to ~50 GHz, and by 2008, should operate to 100 GHz. Observations at frequencies above ~10 GHz are affected by atmospheric water vapor, and are best done in clear, cool, and dry weather conditions. Since Green Bank weather is highly variable, a dynamic scheduling system has been instituted. At present, this system is done by preparing two observing schedules, one for primary (usually high frequency) and the other for backup (usually low frequency) observing. The observing schedule decision is made at noon each day for the subsequent day.

To ensure that programs are completed in a reasonable time, dynamically scheduled programs are given about twice the time that the Proposal Selection Committee assigned to the project. Observing sessions are often paired with a gap of a few days, so that the high frequency observer can choose which one of the paired days he or she thinks will be most suitable. The other day goes to the backup (usually low frequency) observer.

Although this system helps ensure that high frequency programs get appropriate observing weather and can thus be completed during a given scheduling trimester, it does entail considerable overhead for both the observer and the GBT Scheduler. In particular, observing sessions (both primary and backup) can require a lengthy stay at the Observatory.

More details on the rules and procedures of dynamic scheduling are given at Dynamic Scheduling