Background

PG1336-018 is a very short-period (~0.1 day) eclipsing binary system comprising an sdB star and a cool companion, probably a late-type (~M5) dwarf. Eclipses are partial (i~81 degrees) and, because of the very short orbital period, only take about 15 minutes. The reflection effect is substantial, about 0.2 mag in amplitude. What makes the system particularly interesting, and the light curve spectacular, is that the sdB star is a rapid pulsator. In the discovery paper (MNRAS 296, 329, 1998) it was shown that at least two frequencies are present, with periods near 184 and 141 seconds and amplitudes of ~0.01 and 0.005 mag, respectively, although there was some indication that more, lower amplitude frequencies were present. The primary aims of the current WET campaign are to resolve fully the pulsation frequencies with the hope of identifying modes and to search for rotational splitting. Since it is highly likely in such a close system that the components are phase locked to the orbital motion, rotational splitting could be resolved in a few to a few tens of orbits. In addition, it might be possible to model the effects of eclipses on observed pulsations as a way of identifying the spherical harmonic quantum number; to search for phase shifts in the pulsations as a way of directly measuring the orbital separation; and to measure any orbital period changes by accurately timing the eclipse centres (this latter project has already begun at SAAO).

Observing Instructions

The light curve is continuously variable (reflection effect) and the eclipses are rapid and fairly deep (primary ~0.7 mag; secondary ~0.1 mag). The pulsational variations are also usually obvious (certainly through secondary eclipse, though not always during primary due to the rapid ingress/egress) but can be quite small.

RA             Dec          
13 36 13.3     -01 46 34    (1950.0)
13 38 47.6     -02 01 49    (2000.0)
     mv=13.4

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.

Integration times: The observation goal for this target is to measure the pulsations during primary eclipse. In order to correct for the eclipse, we need to resolve the eclipse shape. Therefore, we want to use the shortest integration time possible while still gathering enough signal. Below is a guideline that observers should start with when determining their integration time:

1.9m or greater	1 sec
1.5m to 1.9m	2 sec
1.0m to 1.4m	3 sec
less than 1.0m	5 sec

HQ will evaluate the first night of data from an observer to determine if we need to adjust the integration time. Typically, if observers measure Star/Sky counts > 6, they can reduce their integration time. However, we prefer that observers do not stop observing during a run, especially during an eclipse.

Filters: Use NO filters in any channel.

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. Above all, observers must make sure not to take sky measurements during the primary eclipse!

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: 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
   

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