FO Aqr monitoring for HST - Alert Notice 832

All,

HST is scheduled to look at FO Aqr with the COS instrument starting at 00:40 UT on September 28 (the night of Wednesday, September 27). Because FO Aqr is fairly bright in the UV, the Space Telescope Safety Officer requires observations every night starting a week before the visit and within 24 hours of the visit to be sure COS does not exceed its count-rate limits. 

There is a second visit scheduled to start at 22:30 UT on September 29, so observations should continue through Saturday, September 30.

The safety officer, Serge at STScI, looks directly at the AAVSO light curve of FO Aqr to be sure the star is staying within brightness limits. So if you take data, please calibrate it and load it up to the archive in a timely manner.

Thanks!

You may recall that we looked at FO Aqr last October with HST, but there was a failure to lock on the guide stars, so the data was compromised. This is a second try with different guide stars. 

Let me know if you have questions.

Peter

All,

Thanks to ATE, FRGA, MXD, DANF, HMB, and NROA for observing FO Aqr over the last few days. It is behaving fairly well, but we do need to keep an eye on it every night and observations within 24 hours of the two HST visits.

It has been cloudy here in Indiana for the past few nights. I hope to get some photometry on Friday if it clears off.

Clear skies!

Peter

All,

HST begins its observations of FO Aqr at 00:40 UT Wednesday night/Thursday morning. The safety rules require a magnitude estimate within 24 hours of the visit so that a review board can make the go/no-go decision at 9:00am eastern time Wednesday morning.

A calibrated photometric observation after 00:40 UT tonight and before 12:00 UT is required. 

Pouring down rain here at Notre Dame right now, so not much chance of my getting an observation.

Time-series photometry during the HST visit (00:40 to 04:45 UT Sep 28) would also be very useful.

We do this again for the second visit scheduled for Sep 29 starting 22:30 UT.

Good skies.

Peter

David Messier has pointed out that the Moon is very close to FO Aqr tonight. It appears to be about 8 deg south of FO Aqr, with Saturn in between. 

Given the need for an observation tonight, I am willing to accept the poor photometric accuracy that will come from a large amount of scattered Moon light. Even a point with a precision as large as 0.1 mag should be adequate for the safety decision. FO Aqr does vary by about 1 magnitude over its binary orbit, so we always see quite a variation. 

Peter

HST makes a decision on visiting FO Aqr in less than 2 hours. I do not see any photometric observations in the archive within the required 24 hours before the visit. Has anyone observed FO  Aqr in the past 12 hours and have not posted the results? 

Peter

All,

The HST safety people have approved the visit to FO Aqr scheduled for tonight. Rafael Farfán observed FO Aqr within 27 hours of the visit and Space Telescope accepted that as the final check. Thank you Rafael!

Please continue monitoring as the second visit is coming up on Friday and there is an need for another safety check.

We do two visits because the Earth blocks HST's view of FO Aqr for about half of the spacecraft orbit. By timing a second visit properly, we can fill in the missed binary orbital phases. 

Peter

All,

   I took a quick look at the first three orbits of HST spectra of FO Aqr. The guide stars appear to be good ones this time. The spectra are wonderfully complex with absorption and emission constantly moving around. 

We need a confirmation magnitude tonight to allow the second visit to execute tomorrow. Still cloudy here in Indiana.

Good luck.

Peter

All,

Safety at STScI has approved the second visit to FO Aqr scheduled for 22:30 UT tonight. Thanks to all that reported their observations from last night!

The last thing I will ask is that, if possible, is for time-series photometry during the HST observations. As fast a cadence as possible that still gives precisions of 0.05 mag is best. Looking at the UV data from visit 1, I do not see the typical optical variations of the white dwarf spin pulse and orbital modulation. We can certainly put together and average light curve from all the data, but having simultaneous optical would be reassuring.

It looks to clear up today, so I will try observing FO Aqr from Notre Dame tonight. But sunset is about 0 UT these days, so I am likely to just get the last piece of the HST visit.

Thank you all!

Peter

All,

  I am looking at the HST data of FO Aqr from visit 2. So far it looks excellent. Far more variability in the UV than in the optical...and it is already pretty variable in the optical.

Thanks to Andrew Pearce and Nikola Antonov for attempting overlapping observations with the HST visit. I was able to get about 40 minutes of simultaneous data starting when the sky was still very bright. 

That should do it for the HST observations. It appears that the guide stars locked on this time, so no do-overs. We have lots of data to analyze.

Thank you all for your help! It was critical in getting these observation done.

Peter