Affiliation
American Association of Variable Star Observers (AAVSO)
Fri, 08/30/2013 - 22:31
A new optical observing campaign on T Ori that will run for the month of September is announced in AAVSO Alert Notice 490. Nightly visual or electronic observations (not time series) will be critical to the success of this campaign. So please wake up early (or stay up late), have some coffee, and contribute to the optical coverage of this morning object - make PIs Dr. William Herbst and Rachel Pedersen very happy researchers!
Thank you and good observing - Elizabeth Waagen, AAVSO HQ
Sounds like a good project but there is only one comp star in a 22x22 arcmin fov, at mag 9 at that. The field is so full of GCVS stars that the chart prints black so chosing a check star will be a challenge. Nevertheless .....
Jim Roe [ROE]
[quote=roe]
Sounds like a good project but there is only one comp star in a 22x22 arcmin fov, at mag 9 at that. The field is so full of GCVS stars that the chart prints black so chosing a check star will be a challenge.
[/quote]
Definitely a case where visual observations would be easier, and possibly more accurate than CCD, given the background and comps issues. Even the PI acknowledges this.
Mike LMK
The only comp star in the fov (22x22 arcmin) is identified as a variable NSV2386. It is also the whitest star I've ever seen B-V = -0.017, V-I = -.007.
Hi Jim,
Looking at VSX, this star is shown with range 8.95-9.01V, which means that you would induce a maximum error of about 0.03mag in your measures by using this star as your comparison, if its suspected variability is real (remember, NSV == new SUSPECTED variable). I think that is acceptable for this compaign, if that is the only star you can include in your FOV. Also, T Ori does NOT have to be in the center of the field of view, so you really have ~40x40arcmin from which to choose comparison stars. I see several possibilities if you use that approach.
Arne
Hi,
I have been observing T Ori the past nights. I use comp stars 106 and 114. Over the past 4 nights (last night I had problems with pointing and comp stars are out of FOV). The change rather small (10.11 to 10.13 mag V band).
Josch
The data being reported for T Ori (in V, especially) seem to be inconsistent. I suspect it has to do with the limitations of aperture photometry (a la VPHOT) to handle cases with lots of nebulosity. Is this worth pursuing with VPHOT as the measuring engine?
Jim Roe
Hi Jim,
it seems that the pesent scatter is similar to the one a year ago or so. I do not know if many observers do regular observations like I do. I have been observing this star since the past two weeks nearly nightly and I have consitent data which do not show much variation (at least up to now).
I have observed many stars and send data to AAVSO which are much more consitent than other observers, e.g have a look at QX Pup (not so many observers participate).
I will keep an eye on the star untile end of season.
Regards,
Josch
[quote=roe]
The data being reported for T Ori (in V, especially) seem to be inconsistent. I suspect it has to do with the limitations of aperture photometry (a la VPHOT) to handle cases with lots of nebulosity. Is this worth pursuing with VPHOT as the measuring engine?
[/quote]
There is more variation in the visual estimates! About 0.7 magnitudes, vs. 0.4 for the V. It seems to be more diffferences between observers than actual short term variations of the star?
Mike LMK
I wonder if there is correlation between the comp stars used? Another thing that might affect the measurements in a high nebulosity background would be the radii of the measurement aperture and the borders of the sky background annulus used for the measurements. If the background nebulosity is significant and varies significantly over small angles, then you would increase the scatter. That variation from observer to observer won't necessarily be reflected in larger error estimates of individual observers even if they base error on standard deviation of a check star because individual observers tend to use the same apertures for all their measurements of a particular target. I wonder if it would be possible to get aperture information from contributors. The aperture radii would have to be in angular dimensions or the pixel plate scale would have to be provided. Of course digging out correlations it may be difficult or impossible with data that hasn't been transformed. I don't know how you separate scatter due to (lack of) transformation from variations in background.
Brad Walter
Given the difficulties VSP has with the nebulosity surrounding the variable and comps, I created a realistic chart for the field, using a color deep sky image overlay. I transferred the comps from the AAVSO chart to this image. I placed all the labels in the "2:00" position relative to each star for consistency.
It is attached here as a JPG file. I hope this helps you see things more clearly!
Mike LMK