The Hectospec is a multiobject, moderate-dispersion spectrograph that uses a pair of six-axis robots to position 300 optical fiber probes at the f/5 focus of the converted MMT. The converted MMT’s f/5 focus uses a refractive corrector designed by Harland Epps to provide a 1° diameter field optimized for fiber-fed spectroscopy. The Hectospec consists of three major parts: (1) the fiber positioning unit that is mounted on the telescope, (2) a large stationary spectrograph mounted on a 1.8x3.7 m Invar-surfaced optical bench and (3) a 26 m-long bundle of optical fibers connecting the fiber positioner and spectrograph.

The fiber robots position 300 fibers in 300 s to an accuracy of ~25 µm. Each fiber has a core diameter of 250 µm, subtending 1.5" on the sky. Adjacent fibers can be spaced as closely as 20", but the positioning constraints are complicated due to the tube extending from the fiber button to the edge of the focal surface.

Currently we possess a 270 line mm^-1 grating blazed at ~5000 Å and a 600 line mm^-1 grating blazed at ~6000 Å .The efficiency curves are shown in Figures 15 and 16. The detector array consists of two butted EEV CCDs, each with 2048 (spatial dimension) by 4608 (wavelength dimension) pixels. The gap is parallel to a dispersed spectrum. With the 270 line mm^-1grating the spectral coverage is 5770 Å, with a dispersion of 1.21 Å pixel^-1. The image FWHM is slightly less than 5 pixels, or ~6 Å. The fibers are mounted in two rows; images of even and odd fibers are separated by ~30 pixels (in the wavelength direction) at the detector.

This document is intended for astronomers preparing for observations or attending the instrument at the telescope. The astronomer’s duties are limited to preparing the robot configurations for observing and taking data with the bench spectrograph. MMTO and SAO staff will prepare the spectrograph for observing and will fill the dewar.

2 What to expect at the Telescope

Perry Berlind or Mike Calkins will normally be present during your observing run (very occasionally another CfA person will substitute) to operate the fiber positioner and to provide advice on operating the spectrograph. The CfA robot operator will fill the dewar once a day. Their decisions on operating the fiber positioner safely are not negotiable, and are based on previous operating experience.

The observer’s main responsibilities are to prepare the fields for observation with the planning software, to take data with the spectrograph, and to help replan observations during the night if conditions require a change. Observers should be familiar with the planning software and the instrument constraints described in the next few sections.

The most common error that we have encountered is poor choice of guide stars, including guide stars that are too faint or that are in fact compact galaxies. We strongly recommend guide stars brighter than R=15.5. Observers should use the preview feature in the XFITFIBS software to eliminate galaxies.

Hectospec will be operated in queue mode. Observers may therefore expect to receive a fraction of the clear observing time during each run equivalent to their fraction of allotted time during that run. We try, if at all possible, to observe some of the officially scheduled observer’s fields during their run. If observers are not prepared with valid configuration and catalog files, observations cannot be made.

Currently Nelson Caldwell is responsible for queue scheduling. Nelson attempts to review the submitted files to see if they are valid.

3 Duties for Hectospec Observers

We believe that the queue observing mode for Hectospec and Hectochelle has been a scientific and operational success. The Hecto team and FLWO staff support the operation of the queue in three ways: (1) SAO scientists and engineers have maintained and serviced the instruments as necessary, (2) Nelson Caldwell has scheduled the queue observations, and (3) Perry Berlind and Mike Calkins have operated the robots. The nightly scientific supervision is the responsibility of trained observers from the pool of those with assigned Hectospec and Hectochelle time. The nights covered by these astronomers We divide each Hecto run into blocks of ~3 nights which are managed by one or two observers, drawn from the list of astronomers on the proposals granted time. The nights will not necessarily correspond to the assigned nights on the telescope schedule. We have the freedom to shift the times around for the convenience of observers and the queue. During the assigned nights, the astronomer would attend to the following items, which center around insuring that good quality data are obtained.

Observer Responsibilities

1. Run the spectrograph/CCD acquisition control software

2. Annotate the data logs (now under automation), with comments on conditions, data quality, problems encountered, etc.

3. Check the operation of the spectrograph/CCD at the beginning of the night, and monitor readout noise, spectrograph focus, thermal flexure, etc. Normally, the actual focusing would be done by the robot operators, Perry and Mike, who would also fill the CCD dewar.

4. Be knowledgeable about the fiber assignment code "xfitfibs", in particular with regard to the restrictions on rotator position and guide star selection, to the extent of being able to run the program at the telescope should the need arise.

5. Be knowledgeable about the normal sequence of operating the positioner and acquiring fields, so that when problems with acquiring a field occur, the robot operators can be advised as to how to proceed (e.g., moving on to another field because of poor guide stars). This would not include actually operating the positioner; that task would remain in the capable hands of trained personnel.

6. Do quick look reductions of data as it appears, checking for overall quality, and in particular insuring that the spectra fulfill program goals. E.g., are objects detected at all (coords ok?), are objects underexposed or overexposed, etc.

7. Help make decisions regarding the queue during times of marginal weather or seeing, choosing targets from the nightly list. Normally, the nightly observations are scheduled by the queue manager (Caldwell at this time).

To aid the on-site astronomers, each group with Hectospec time will be expected to supply a brief summary of their data and calibration requirements.

4 Fitting Fibers to Targets, Running Xfitfibs

Here is the current operation mode for Hecto observing runs.

(1) The PI makes a catalog of objects, which may be ranked in preference. The catalog must also include guide stars on the same coordinate system. Guiding is done at the edge of the Hectospec field, not on the surface where the object fibers are positioned. Thus, there are very stringent requirements on guide stars by the small area of sky available and the limited range of magnitudes allowed by the TV cameras.

The 2mass and GSC II catalogs can be used where an observer catalog is minimal in stars. In that case, the program tmcguidestars should be used. This program searches the 2mass catalog for coincidences with the observer catalog, and computes a coordinate transformation. 2mass and GSC II stars are selected in the field, transformed to the observers' catalog coordinate system, and added to the catalog. Note: the target catalog must have some stars in common with the 2mass catalogs. You might need to add stars to insure that, even if you don't intend on observing them. Bad News tmcguidestars is not yet ready for export. It does run on CfA computers, in a command line mode. External projects should contact instrument scientists if they need help with guide star selection.

(2) The PI downloads the configuration program from CfA,
cfa-www.harvard.edu/~john/xfitfibs/
and runs the config program for approximate dates of observation. In this process, guide stars are checked for suitability using a number of criteria (magnitude range, not a galaxy, no neighbors, etc).

(3) xfitfibs requires information such as date and length of observation, number of exposures, ranking of config, grating or filter and binning, all which will be used in scheduling. The output of the program is a number of files which would now be sent to a CfA computer for human checking, via the button Submit . After they are checked at CfA, the configuration files are sent to a computer at the MMT.

(4) The configuration file is modified at the telescope a few minutes before the observation takes place, in order to update positions, rotation angles, random sky selections, and guide stars.

Please submit your configuration files at least 10 days before the run starts.

4.1 Brief Instructions for Xfitfibs

Here, I describe the basics of obtaining a fiber assignment file from a catalog. The xfitfibs program itself contains many pages of help for particular items, and after going through these steps, one should consult those pages for detailed help.

4.1.1. Make a catalog

The catalog should be in starbase format (Tab delimited) with at least these columns:

ra dec type

but it's probably better to have more:

ra dec object rank type mag

A sample catalog would look like:

ra	dec	object	rank	type
--	---	------	----	----
0:40:30.289	41:16:08.73	008-060	1	TARGET
0:40:31.566	41:14:22.54	010-062	1	TARGET
0:32:00.0	42:00:00.0	sky	2	skyobject
0:38:10.2	41:43:23.2	2mass19352	(tab)	Fiducial
0:54:58.594	43:05:22.298	(tab)	(tab)	guide
0:54:59.146	39:03:36.815	(tab)	(tab)	guide

Note the row with dashes (also tab delimited). "guide" indicates the guide stars, located at the end of the file. In this case, the guide stars have no rank or object name (but the tabs are there). A type of "skyobject" may be used for specific assignment of background - these are treated by xfitfibs the same as "target". "Fiducial" is used for objects that help define the coordinate system (e.g., bright stars), but which should not be
assigned to fibers. Rank is used by the program to order the target assignments - Lower numbers are assigned f