AAVSO Alert Notice 501 describes a new observing campaign The target is the CV SBS 1108+574, scheduled to be observed bt HST/COS in mid-May.
Many thanks and good observing,
Elizabeth Waagen, AAVSO HQ
I want to thank MGW for the early May observations of SBS 1108+574. At CV~19.5 it sets the quiescence level for this star. The Space Telescope folks are relieved that it continues to be faint with just a week and a half before the HST 6-orbit visit.
Peter Garnavich, University of Notre Dame
The exact time of the HST/COS observations of the CV SBS 1108+574 has been REVISED to May 16 UT. YOUR OBSERVATIONS IN THE UPCOMING NIGHTS WILL BE CRUCIAL!!
Please see AAVSO Special Notice #384 for time and other details. This observing campaign was announced in AAVSO Alert Notice 501.
Thank you for your observations, and good observing,
We have been mostly cloudy or completely overcast every night since last Thursday except for Saturday night. The forecast for tonight and tomorrow morning is overcast as well. Hope tomorrow night offers some chance. At least last night we got over 3 inches of rain and not just clouds, so I am not complaining. Central Texas is in the worst drought since the 1930s dust bowl.
Brad Walter WBY
I was able to observe SBS 1108+574 last night. It was pretty faint in a 5 minute clear exposure with a 12 inch. In fact, I had to stack 26 of them to locate the variable. When I did, I found 2 stars very close. I had to use an unusually small aperture to exclude the second one. Not sure which is the target. I used the one to the North--ie the brighter of the two. Is this correct?
Gary, if you plot a G-scale chart and use the DSS image option, you can split those two stars. It appears to me that the Southern of the two stars is the target - that's where the crosshairs sit.
There is a source just 10 arcsec north of SBS 1108+574 that is similar in brightness when the CV is at quiescence. It turns out that the source to the north is a compact galaxy, but is still gives you the idea of the faintness of SBS 1108+574 when it is down.
I want to thank everyone that is watching this star as the deadline approaches. I have never done this go/no-go decicsion thing with an HST observation before. It is exciting!
The weather in South Bend has been awful and it looks poor for Wednesday night as well. So I will not be able to help with the monitoring.
Thanks Peter for confirming that. Also, thanks Brad for digging into Alladin etc. I, like Arne was surprised that no mention of the close companion had been made by others. I was late to get on to this because of weather. Just wanted to make sure of what I am seeing.
Looks poor for tonight. Hope for Wed Eve.
Weather looks good for LA (95 degrees F here in the day!). Will definately use my ST-10's water coolng option to get to -16 tonight. Hope to take 15x60sec exposures at 2x2 bin through the clear filter and process in MaximDL as CV photometry.
I just took two snapshots, 60 seconds long, with V filter.
The star is fainter than 18 mag as i could not even find it in the picture while other stars of about 18 mag did show up.
Time was 21:10 UTC.
I will take two more pictures in a few hours.
Observatorio El gallinero , El berrueco, Madrid(Spain).
AAVSO code: CDZ
This is a very faint object. I was unable to get it in a 300 second exposure, in a Clear Filter, with a 12 inch and a back illuminated ccd with very high qe. May be sky limited here on Cape Cod. You may need a lot more exposure to get it. I only saw it after stacking 26 of these 5 minute exposures, and then it was just visible.
Be interested in how you do tonight. I am clouded out, it looks.
This CV is definately on the faint side. To clearily identify it, I used the F-scale finder chart (18' width) with the DSS image instead of the usual star chart format. I'm submitting my 3-days of observation tonight.
Thanks for the comment. I already used the "F" chart and the DSS image, and its not clear. My stacked image of 130 minutes, clearly shows 2 stars at the approximate location of the target. My concern, is whether the brighter or the fainter one is the target. (Is the target the northern or southern star? They are separated by maybe 3 arc seconds for me) I have also attempted to use the "G" chart, but the target icon makes it hard to see which star is being designated. Also tried to not used the DSS image, and it did not clear up the confusion.
Have you stacked and aligned your images? Do you see 1 or 2 objects where the target is supposed to be? Maybe your are seeing both in a single image? My seeing last night was not as good as normal, so I cannot see the semblence of a target in any single images. We also had high cirrus last night, which does not help.
Your positive V observations of SBS 1108+574 are crucial tonight and PARTICULARLY TOMORROW NIGHT. The HST scheduling team has specified the window on 2014 May 14-15th during which they require photometry in order to make their go/no-go decision on the morning of the 15th for observing on the 16th. Please see AAVSO Special Notice #385 for details.
Many thanks and good observing,
The bright moon is interfering some, but last night it was fainter than 18.5 CV - the first night I could not even detect it. Previous week's measurements all 19+.
Thanks for the excellent observations, Gordon! Please keep up the good work!
Sincere thanks to all of you who are following this challenging target!
Since both stars are faint, it doesn't matter whether you report one or the other or include both when checking for an outburst. I'm surprised that none of the researchers, including those using big telescopes like Gemini, have reported a companion. I'll put the field on the TMO61 queue, assuming that the weather improves and the clouds clear, to see if I can ascertain which one is the true variable. However, the coordinates should be enough to make the positive identification, as they won't be 3arcsec in error.
I revisited the "G" chart with DSS and I agree pretty much that the Southern most of the two stars near the target location is the target.
I extracted my earlier PT from AID which was done on the Northern most star and redid the PT with the Southern most target. Its another magnitude fainter and averages about 20.
I guess HST would not care which of these went into outburst. BTW: I measured the separation at 11 arc seconds.
Using Aladin to view the DSS image at high magnification it seems clear the correct star is the southern one. The crosshairs in the attached image are at exactly the target coordinates. The center of the slightly dimmer star to the N is 11 arcsec away at 11 11 26.87 +57 12 49.9. The DSS image shows nothing between these two stars.
Brad Walter, WBY
Here is another view from Aladin with the NED database overlayed. the highlighted object (the southern one of the two is identified as SBS 1108+574. The upper object is galaxy SDSS J111126.99+571249.0 at mag 19.6g.
SBS 1108+574 was not detectable tonight in a 5 minute V filtered CCD image with a 14 inch telescope. There were thin high clouds and a very bright sky background from the almost full moon. Just to quantify things a bit, in this image the nearby AAVSO comp star "152", about 2 arc minutes south of the variable, has a SNR of 39. UT time of observation from the FITS header: '2014-05-14T05:13:30.343'
Your observations are consistant with what I have been seeing here on the East Coast. I don't even get a good image with unfiltered and a 12 inch scope. I have to stack to see the target and its companion clearly. Better luck tonight--hopefully.
It looked like it was going to clear last night from Cape Cod. Got things going and then it caved in again. I left things running for a couple of hours, but did not get a single image. Hope that Wednesday night is clear. Forecast looks dubious.
I just barely saw it after combining 5x60 sec exposures taken through a clear filter with ST-10 with my AO-L running and some water cooling going. Although the moonlight played havoc with the sky background, I was able to get a few Cv magnitudes of this variable just brighter than 19th (at times) with an error of +/- 0.25.
What kind of FWHM values were you able to achieve?
"What kind of FWHM values were you able to achieve?
I think I'm getting from 2.2-3.5" FWHM. Since I'm using a relatively dim guidestar, some of my shots are lost as my guide star integration times are 1.2 seconds. I'll post one of my better shots when I get home.
Using the iTelescope 24 inch Planewave I was able to measure SBS1108+574 at mag 19.5 CV this evening. Full measurement submmitted.
CSS 120422:111127+571239,2456792.69237,19.520,0.131,CV,NO,ABS,152,-6.963,162,-5.954,1.0793,na,13378TXK,Non-standard filter: LUMINANCE - T24 iTelescope - Aubrey California
I get 19.16+/-.2 at 2456792.7344. 30" Dob, 150s Luminance filter. Bright moonlight.
Variable is certainly not bright!
R. Stanton (STR)
I finally wised up and adopted Gary's strategy, stacking 5 unfiltered images, each of 5 minutes exposure.
I saw two sources at the predicted position aligned almost exactly N-S and a few seconds apart. I didn't try to measure them but they were of approximately equal magnitude and very faint. The ballpark of 19th magnitude reported above seems about right.
It was clear for flats, but clouded over at dusk. I managed 16 images of 5 minute duration thru the clear filter. Only 4 gave a star field. Stacked the 4 and could not see the target, nor its companion. Plate limit was 17.4. These observations from JD 6792--ie Wed night.
I Stacked 10 x 2 min images with midpoint time of 04:11:45 UT. I could not see SBS 1108+574 on the image. Photometry at the WCS location of the object gave S/N <1, I did have a positive net count and a calculated magnitude of V 20.2 +/- 2.0. I recorded V 19.1 +/- 0.8 for SDSS J111126.99+571249.0, the galaxy 10 arcec N. I regard the galaxy to be at the absolute extreme of detection for me under last night's moon conditions. I am pretty sure that I erroneously reported the galaxy rather than the target in my previous report. I will modify that report to fainter than.
In any event, SBS 1108+574 is definitely not in outburst.
I checked the coordinates carefully and my May 4th report report was for SBS 1108+574 not the galaxy.
Brad Walter, WBY
I just got word from STScI that the AAVSO observations convinced the safety team to go ahead with the visit to SBS1108+574. Thank you all for the observations. They were difficult with the Moon and the very faint target.
HST will begin observing SBS1108/CSS1204 Friday morning. We have 6 orbits in a row (which is not normal, the limit is usually 5) so the visit will last 9 hours. Observations over the next couple days will constrain the state of the star during the long HST visit.
I am curious about something. Now that we have the past 16 days showing SBS 1108+574 in quiescence, how does that suggest to the safety team that the object is going to be in quiescence for Friday and Saturday, when HST is scheduled to observe?
It would seem to me that the safest time to observe a CV is relatively soon after an outburst.
That is a good question, and I don't know the answer. For SBS1108 which outbursts once a year or so, allowing a 24 hour window means less than a 1% chance that it will go off at observation time for a random distribution of bursts. This may be acceptable. Also, I think the COS detector will shut down if counts exceed some limit and it will go into safe mode. This protects the detector but probably ruins the planned observations down the line.
Thanks again for getting the observations that cleared our program.
I submitted 3 sets of 5x60sec clear filter exposures of this field. The object was never brighter than Cv 18.95 magnitude. Here's what I got:
Here is a "cleaned-up" image of all 16 good shots I got last night
Its clearly seen even though MaximDL reports that it's at a CV magnitude of 19.101 +/- 0.123 for the total stack of 16 images. Despite the heat & moon I'm able to go this deep from 8 miles NE of downtown Los Angeles, CA! (Santa Ana conditions make clear skies). Instrument used was 33 cm classical cassegrain at F/7.4 (2400mm) with water cooled SBIG ST-10XME and AO-L guiding at 1.2 seconds; Note: water cooling was a must as the temperature when I came home was 100° F.
did anyone look at the CRTS transient data from April 2012 referenced in VSX. This CV really brightens in outburst. http://nesssi.cacr.caltech.edu/catalina/20120422/1204221570344112356.html
I looked at the 2013 PJ Carter et. al. article, 2013arXiv1301.6761C, also referenced in VSX. It has some good light curve data on the decline from the outburst but I couldn't find any data leading up to an outburst, which isn't surprising since the outburst of this object seem to be infrequent.
Due to the bad weather I have submitted only the measurements from two nights: 8 and 11 of May. The object brightness did not exceed 19.77 mag in TriG.
The attached image is stack from 15 x 120 sec frames with 12”RC telescope, ATIK 4000M at -30 deg.
This is what I got after summing 12x60sec exposures last night (4 out of 16 omitted because of haze/mis-guiding):
JD, Magnitude, Error, Filter: 2456793.437336,19.444,0.200,CV
Looks like its a nice faint target for HST.
I got results last night that agree closelywith FJQ combining 6 x 5 minute exposures with a 250mm aperture telescope. This is the first time I have been able to easily see the target on the image without knowing exactly where it was.
Here is what I got tonight on SBS 1108+574:
Still in quiescent phase at <19.7 CV magnitude (+/- 0.25). This will probably be my last observation on this rather quiet variable.
Observed SBS 1108+574 last night for the last time--time to move on. It was still in quiescence. I went a little longer than asked.