FO Aqr campaign

Hi All,

I think I need some help on the FO Aqr campaign. For my photometric observations I have always used BVRI filters, and when appropriate have used TG to transform the data. I have never used CV observations, so I am unclear as to how I should go about taking unfiltered images with a V zero point per Dr. Littlefield’s request. I do have a clear filter, but I do not know how to acquire and apply a V zero point to those C images. I use Maxim DL for image acquisition and AIP4WIN to reduce the images.  Can someone either please enlighten me as to the process or give me a link that will explain the process?

Thanks,

Keith Graham  

You should analyse your Clear filtered data and then for absolute magnitudes use the V magnitude of your comp star.

Josch

Thanks a bunch Josch and Colin. That is very easy to do. Somehow I thought it was more complicated than that. Now on to the photometry.

Cheers,

Keith

I processed my first time series of FO Aqr, using Luminance images and V mags for comp and check stars.  MaxIm DL 6.13 will happily generate an AAVSO report, but WebObs chokes on the Lum filter -- not allowed.  Hrmpf!  How do we report the data, then?

Hi Brad,

Luminance works with FO Aqr because it is a cataclysmic variable, which means in general that (a) its color doesn't change during either quiescence or outburst; and (b) it has a color fairly similar to the comp stars.  So in this case, your measures will have some offset from those taken with a V filter, but that offset remains reasonably constant and could be removed by a researcher.  It often helps to use luminance or some other wide filter when working with faint objects (a larger-aperture telescope is really the better choice!).  Where using luminance as a surrogate for V fails is for the rest of the astrophysical zoo.  A star that changes color during its cycle, like an eclipsing binary with dissimilar temperature stars, or a pulsating star that gets hotter near maximum, will give offsets that aren't constant, and so your light curve will look different from everyone else's.  Other stars, like novae, have huge emission lines that fall outside of the V filter but impact unfiltered measures.  It gets even worse for red stars like Miras - then you have a huge color difference between the variable and the comps, you have to worry about second order extinction effects, etc.  If you are observing unfiltered, try very hard to stay near the zenith and don't get into high airmass regimes.

So use luminance, or unfiltered, when you understand the issues involved and you really need that additional throughput.  Use filtered photometry for all other cases!

Arne

Submitted ~325 more data points from last night:  20 sec Lum images with 17" f/6.8 yields an SNR of ~100.  What an interesting system!

I worked with a college student on another "polar" (AI Tri) last fall semester, which also had a rapid fluctuation as this one does.  Mind bending to try to appreciate all that goes on with these uber-high magnetic field stars.

Hi,

I am still confused as to how to use the C filter data and V comp star mag to derive the CV mag. I use AIP4WIN to reduce my date. Below is a line from the my date for FO Aqr from Oct. 7, 2016.

FO Aqr;2457669.57412;0.242;0.043;CV;NO;STD;000-BJN-854;13.361;000-BJN-853;11.667;1.6458;na;X16353BIR;(No comp star data for CV filter.)

Note that the mag for FO Aqr is 0.242 and the mag for the comp is 13.361. Since there are no C filter  mags given on the photometry chart, I am assuming these mags are instrumental mags. Is this correct? Then would I simply add those two mags to get the CV mag? If so, I could do this using Excel by creating a new column for the results and replace the original results the with the new ones. Or is there a simpler way to do this?

Thanks,

Keith   

My colleagues and I would like to thank everyone who has observed FO Aqr. Our first paper about the ongoing low state has been accepted for publication at The Astrophysical Journal, and 17 AAVSO observers are co-authors on the paper. A preprint of the accepted version will appear on astro-ph within the next few days.

We are still actively monitoring the ongoing recovery, so please continue observing this system at fast cadences. We prefer cadences of 30 sec per image or faster if you can achieve an acceptable signal-to-noise ratio at such a cadence. The average magnitude of FO Aqr has recovered to V~14.2, so this should be feasible for many observers.

We'd like to monitor FO Aqr until it fully recovers, and if the recovery continues at its current rate, we expect this to occur in about two months.

Best Wishes,
Colin

Hi Brad,

FO Aqr is at -08:21 declination, and you are at +44 latitude.  You can do the math, but I would expect the geostationary band to be pretty close to that field center.  It was at -5 declination from Flagstaff.

What is fun is to shut off the telescope drive and do imaging of the satellite.  They are often about 9th magnitude and very easy to do, and during some seasons, actually get eclipsed by the Earth.

However, in the meantime, it is good that New England is getting clear weather just when needed for the campaign!

Arne

AAVSO Special Notice #425 announces the schedule (November 13-14) for XMM-Newton observations of the intermediate polar FO Aqr, the target of the campaign announced in AAVSO Alert Notice 545. Time series photometry is needed for simultaneous coverage during the XMM-Newton observations and after. Please see the Special Notice for details and instructions.

Many thanks and Good observing,

Elizabeth Waagen, AAVSO HQ

Looking clear as a bell here in Vermont.  Dome is open, instruments cooling, new calibration images already taken, now just waiting for twilight to come to an end...

Clear skies,

Brad Vietje

Newbury, VT

I was thinking the same thing about the conference. I got about 3.5 hours of data (uploaded) - see attached. It was 60 seconds in V with a C14. I look forward to seeing how/if your data overlaps mine.

Hopefully the XMM-Newton run took place as planned.

--- Dave LDJ

Remember that discussion of geostationary satellites?  Well, I had one ruin an observation, and I failed to catch it until after submission, when I saw the discrepant point on VStar.  I should have checked the data more carefully before submission, but working at 1:30 AM has its drawbacks, as well as long time series of over 600 images.

 The attached image does make a good demonstration of the importance of reviewing every image, not just sampling every 10th frame!

I've reported it as discrepant -- my apologies for the extra work, Sara!

Clear skies,

Brad Vietje

Newbury, VT

My colleagues and I are very pleased with the coverage by the AAVSO. Thanks for the great work, everyone! It will facilitate the analysis of the X-ray data.

Best Wishes,
Colin

Hi Everyone,

I have attached an updated long-term light curve of FO Aqr. Different data sources are shown using different marker styles. The horizontal dashed line shows the median magnitude of the bright state based on long-term CRTS data. You can see that the recovery has stalled about 0.2 mag fainter than the bright state (as measured by CRTS). The thick, red line is an outlier-resistant linear fit to the recovery, and the bottom panel shows residuals from the fit.

Each data point (except for a few of the blue squares) is the median magnitude of FO Aqr during a time series. This helps to prevent short-period variations from contaminating the long-term light curve.

I know that FO Aqr is getting close to the Sun, but please keep up the good work.

Best Wishes,
Colin