APF Starlist format and requirements

To observe with the APF requires that you construct a target list which is fed into the observing software. This contains information about the star such as its coordinates, but also contains when the star should be observed and the configuration of the instrument. We show an example below.

HD185144 19 32 21.59 +69 39 40.24 2000

pmra=598.07 pmdec=-1738.40 vmag=4.68

texp=900 I2=Y lamp=none uth=00 utm=00

expcount=1e9 decker=M do= count=1 foc=2

In each section, we discuss the various components of this listing and the requirements. Some components are optional.

Please see the description of coordinates for important details regarding specifying how the telescope software points.

We provide the full manual for the observing software as well.

Object ID

The name of the object is required. The name should be an identification that can be used to reference the object in the Simbad database. We use that database for confirming object coordinates.


Object coordinates and magnitude

The coordinates should be in sexagisimal format with each component separated by spaces. A plus sign is optional for positive declinations. Following this must be either 2000 or the epoch for the date of observation, so 2000 is preferred. Finally, the proper motion is specified as a pair of keywords with the value in milli-arcseconds per year, just as Simbad returns it. The target list must include a v band magnitude, which we use as a measurement of the transparency.

19 32 21.59 +69 39 40.24 2000

pmra=598.07 pmdec=-1738.40


Exposure time

The maximum exposure time in seconds should be specified. We have an exposure meter for the guider on the APF. This will report the photon-weighted midpoint time of the exposure. It can also be used to curtail an exposure after a certain number of photons have arrived on the guider.


Calibrations During the Exposure

We have two flags for calibrations. One of these flags selects the iodine cell and can have a value of "Y" or "N". The second is a placeholder for taking a ThAr exposure before the exposure and must be "none".

I2=Y lamp=none


The preferred time of the night of that the exposure should be taken is expressed in UT hours and minutes. The hours and minutes are separate key-value pairs.

uth=00 utm=00

Exposure Meter Value

A total number of counts on the guider can be requested as a way to terminate the exposure. A total count of one billion yields a signal to noise of 100 or so spectrum. If the requirements are that the exposure run the full exposure time, an exposure count of a 100 billion should be more than sufficient. The final number of photons counted by the guider will be recorded in the header.



The aperture used for the opening of the spectrometer is specified by a single letter. Below we list the decker codes with the sizes in arcseconds

  • K - 1 by 12 arcsec
  • L - 2 by 12 arcsec
  • M - 1 by 8 arcsec
  • B - 2 by 8 arcsec
  • W - 1 by 3 arcsec
  • T - 2 by 3 arcsec
  • S - 0.75 by 8 arcsec
  • N - 0.5 by 8 arcsec
  • O - 8 by 8 arcsec


Pointing Check

The standard alignment process is to place the brightest object in the 22 arcsecond search radius on the slit. To perform a pointing check and then require a 3 arcsecond search, put any character after the = in the statement below. do=no or do=0 will still perform the pointing check.



Additional Exposures

By default, the software will only take one exposure, in effect count=1. By specifying count=2, two exposures will be taken. Large numbers of exposures on the same target can be tricky because of the requirements for the telescope shutters. Please contact the APF staff before attempting such an observation.



Focus check

By default, the APF will check the focus on objects that are apparently bright enough. This can be turned off to speed up the observing process. The brightness requirement is that frame rate on the guider one image per second or faster. This focus check measures the FWHM of the image on the guider at the current focus and on either side. If the offset is too large, then a focus sweep of seven positions will be run. Setting foc=2 forces an actual focus measurement. Setting foc=1 forces the focus check, in case the default behavior is changed to turn off the focus check.


The Whole List

We tie all of this together in an example star-list.