Sources, Resources, and Sessions

by Gustaaf Van Moorsel last modified Nov 19, 2014

For the VLA, the primary substantive change between the earlier text submission process and proposal submission through the PST is the way in which observing requests are structured. The PST employs the concept of sessions, long in use for GBT observing requests. Generally a session represents a contiguous block of observing time. A session describes the amount of time requested for that block, and how it should be divided amongst various sources and resources. Many observing runs involve a single observing session per day. A proposal may request multiple observing sessions, either as repeats of the same session (for example, in monitoring observations), or as truly independent sessions (for example, in multi-configuration VLA observations). For the VLBA/HSA or GMVA, the sessions are structured in the same way as for the VLA.

Within the PST, each session is specified as one source group/resource group pair for the GBT, and as one or more source group/resource pairs for the VLA, VLBA/HSA, or GMVA. The concept of a source group or a resource group is intended to make it easier to handle observations of a large number of sources or resources within a single observing session. The resource specifies the telescope setup to be used in observing the sources within a specified source group: the front end receiver, the back end, and the technical details of how they are to be used together. For the VLA, VLBA/HSA, or GMVA, resources are not grouped.

Each session has additional information, including a session name, a minimum start LST, a maximum end LST, a minimum elevation, a total session time, a counter for the number of times the session is executed plus a separation interval, text describing scheduling constraints, and text giving comments. Some of this information is not applicable for the VLBA/HSA or GMVA and is replaced by other parameters (e.g. minimum start GST, maximum end GST). For the VLA, VLBA/HSA, and GMVA, each source group/resource pair has an associated observing time and rms noise level, and the total time for the session is normally the sum of the observing times requested for the constituent source/resource pairs. For the GBT, the total observing time for the session is manually entered.

Most simple proposals fit fairly naturally into this scheme; some will not. At the moment those edge cases'' are handled primarily through the session's comments box. One can also manually over-ride the simple sum of pairs'' calculation of the total observing time for a VLA, VLBA/HSA, or GMVA session. If you are not sure that your session accurately represents what you wish to do, you are strongly encouraged to enter a text description in the appropriate comments field. If many proposals require similar tweaking, we will consider extending the concept of sessions to handle those cases.

The practical details of constructing sessions are described in the separate Sessions Section.  Examples of how one might use sessions to handle various types of observing are provided for the GBT and the VLA.