Background

PG 1654+160 is a pulsating DB white dwarf star (DBV). Currently a project to investigate pulsational group behaviour of the DBVs is being carried out, obtaining single- and small multisite data sets for all stars with few available observations.

PG 1654+160 is of considerable interest for low-priority WET observations because it is believed to have many pulsation modes excited and because its frequency spectrum varies with time. We will test these beliefs.

If you have an online display on your telescope, pulsations with a time scale between 8 - 15 minutes and an amplitude between 0.05 and 0.2 mag can be roughly expected - unless the star's pulsational behaviour has changed dramatically.

Please consult the scientific justification for more information.

Observing Instructions

RA             Dec          
16 56 58    +15 56 25   (2000.0)
     mv=16.15

Run start: Please start your run on an integral multiple of ten seconds (times ending in "0"). Check the computer clock just before the start of a run, synchronizing with your master clock to within 0.1 sec if possible.

Calibrations for CCDs: Please make sure to collect a sufficient number of bias and dark frames as well as flat fields for every night (whenever possible).

Integration times: Using a photoelectric photometer, 10-second integrations are suggested.

If you have a CCD, we recommend:

Telescope aperture	CCD readout	Integration + readout time
less than 1.0m	frame-transfer	20 sec
larger than 1.0m	frame-transfer	10 sec
any size	5 seconds or faster	20 sec
any size	slower than 5 seconds	30 sec

Note that the times given INCLUDE readout, e.g. if you have 4 seconds readout time, please choose 16 seconds as your integration time to obtain one data point every 20 seconds. Do not choose integration times longer than 30 seconds as this will undersample the pulsations.

Should the recommended integration times produce count rates higher than half of the saturation limit of your CCD for the variable or potential comparison stars of similar brightness, feel free to use smaller integration times.

If you have the possibility to window your CCD frame to decrease the readout time, please do so by keeping the variable and at least two comparison stars (excluding the close companion) of at least the same brightness as the variable on your frames.

Filters:

1. Photoelectric photometer: Use NO filters in any channel.
2. CCD: A red-cutoff filter is desirable, as PG 1654+160 has a companion of similar V magnitude only 4" away. This companion is very red, and it will not contaminate the photometry when using such a filter. Possibilities are a CuSO4 filter, BG38 or BG 39 glass or, for large telescopes only, a Johnson B filter. Please contact HQ should you have questions.

Guide Stars: Please consult the finder chart and use one of the two stars marked there, if possible. Also record your ch2 offsets and telescope plate scale so we can verify exactly which star was observed.

Sky calibration: Observers with 3-channel photometers should record sky in all three channels near the beginning and the end of each run to permit accurate cross-calibration. Observers with 2 channel photometers should take sky by moving the telescope. We have sometimes in the past used the channel 2 verniers to measure channel 2 sky (only) but we find this is not really reliable. Try to take sky as often as needed, at least once per 1/2 hour, for 4 or 5 good sky points; more are not needed and cause unwanted data gaps in the light curve of the target star.

Apertures: Please use the smallest aperture consistent with getting data of good quality (e.g. no visible loss of light to the edge of the aperture). A general rule of thumb is to use an aperture approximately 8-10 times the diameter of the seeing disk. Record the size of the aperture (in arcsec) in your observing log.

Control Center: The XCOV 21 control center is at Iowa State University's International Institute of Theoretical and Applied Physics (IITAP).

Contacting the Control Center: Consult the Phone Contact List for information on phone, fax, and email for the control center as well as the other sites for this run.

Time Check: Please do a clock time check each night before taking data and verify your time with HQ at the beginning of the run, and as often during the run as possible. HQ will have an accurate clock available for phone clock checks.

Data Transfer during the WET run: There are two ways to send your data and logs at the end of each night.

1. By FTP to: wet.physics.iastate.edu
   (Note that this has changed from the previous site of wet.physics.iastate.edu!)
   The username for the FTP site and the password is available through email. This information is only available through email because we have had problems with hackers filling the FTP system in the past. This is not an anonymous FTP transfer, so you will need the username and password to upload your data. If you use the FTP option, load your data into the "wet/incoming/xcov21/" directory.
   
   
2. Via e-mail to: wet.physics.iastate.edu
   

Post-WET run transfer of the CCD data: Please write your frames to DAT tape or CD as FITS files and mail them to:

Gerald Handler
South African Astronomical Observatory
P. O. Box 9
Observatory 7935
South Africa

We leave it up to you if you would like to send your raw frames or partly reduced (overscan, bias, dark, flat field) data. It is however important that the photometry be performed homogeneously, so please refrain from sending the time series only.

Observing Logs: We ask that you send a copy of your observation log along with the data, at the same time if you can.