I am a beginner in photometry and have the software and hardware ready to do some photometry observations. I was wondering if anyone could recommend a good variable star that I could use as a "first star" exercise. It would have to be in the east after sunset (Eastern time), show variable pattern that can be captured during several hours of observation, and have reliable comp stars nearby to use in the analysis. I would need the name of this star and it's coordinates (I think TheSkyX uses JNow coordinates). Brightness is not an issue as I have a relatively powerful telescope and CCD camera but it would help if the percentage change in brightness was large so the pattern could be recognized.
Also, could you please tell me how to get a chart of this star as it would appear in my telescope so I can readily identify the comp stars to use? My field of view is 31'x31'. Thanks.
Ed,
Welcome to the AAVSO and congradulations on being ready to observe Variable Stars.
I think some of us would be better able to help you out if we know your scope specifics: reflector or sct; the mirror diameter and the focal ratio; also it would be advantageous to know your CCD model and mfg and whether or not you have a V filter, at a minimum.
Also, when you mention a few hours, do you mean 2, 3 or 4; this is important to know when looking at possible targets that would meet your criteria.
Charts are available through the Variable Star Plotter (aka the VSP):
https://www.aavso.org/apps/vsp/
Their is a Help Guide for the VSP available and a good starting place, although the image shown is an older version as you will realize when you first open the VSP:
https://www.aavso.org/files/VSP_Help.pdf
Here is my email address in case you might wish to have it along the way: tcarchcape@yahoo.com
Tim Crawford, CTX
Thanks Tim. I really appreciate it. My scope is a Planewave CDK20 which is a 20" Corrected Dall-Kirkham scope. It has a 6.8 focal length which is about 3400mm. The camera is an Apogee U230 which has a 2048x2048 pixel chip and a 96% peak quantum efficiency. The combination provides a field of view of about 31'x31'. The filters I have available are: L, R, G, B, CBB, NIR, i' and z'. The scope can do a good job with stars that are relatively dim. As far as the length of time (a few hours), I could in theory start tracking the star when it's 20 above the horizon and my mount which is a G.E.M. can track about 90 minutes past the meridian. Please let me know if there is any other information that would be helpful.
Ed
I'd suggest a delta Scuti class star. Here's a list:
http://www.vikdhillon.staff.shef.ac.uk/teaching/phy217/info/delta_scuti…
The best delta Scuti stars (shorter periods with decent amplitude) in that part of the sky don't seem to have AAVSO CCD sequences. We could ask Tim to make you a sequence for GP And or BL Cam. Both have 4th and 5th magnitude stars nearby to make them easy to find. But, for a "first star" to make a neat light curve you don't really need to have an carefully made comp star sequence. You just need a couple of non-variable stars nearby, of about the same magnitude as the target, to have a single comp star and a check star.
As Tim mentioned, you can use the Variable Star Plotter on the AAVSO home page to make finder charts. If you like, you can also contact me privately to help you pick a comp and check star and for help to get you started.
Phil ( navillus at sonic dot net )
Great. Thanks Phil. I use TheSkyX software which can pinpoint the star if I have it's RA and DEC. I'm not sure but I believe they use JNow. Then if I have a chart that is reasonably close to the 31'x31' field I could easily recognize the star and any comps nearby.
Have you made a T-point model to improve the pointing of the telescope? If so, that will make things go a lot more smoothly.
About using RA and Dec: I'm sure SkyX includes the General Catolog of Variable Stars database. You'll only need to enter the GCVS name to go to the star. For example, for SkyX input: "GCVS BL Cam" without the quote marks . This should take you right to it, or a least get you close. At least this works for my Sky6 software, the predecessor of SkyX.
Phil
Ed,
You have a great setup-wow.
I have to agree with Phil that BL Cam would be a good candidate meeting your criteria. I have several lists of rapid changing targets but I fear they are mostly two bright for shorter periods and time of year.
The period of BL Cam is around an hour and you should see a change of ~ 1/3V in that time period.
The downside is that there are no comps available that match any of your filters! If you want to do reportable photometry you should consider a photometric V filter at a minimum (and this one filter will sever you well for a long time. Even a Clear filter would allow you to observer cataclysmic variable (B-V = ~ 0) and report them. Johnson Cousin Filters are the ideal, at this time for photometry.
I apologize that I really don't have any other immediate options for you at this time.
Tim
Thanks Tim. Apparently the J2000 coordinates of BL Cam are 03 47 19.880 +63 22 42.13. I could probably set TheSkyX to use J2000 coordinates.
As far as the filter, I have one empty spot on my filter wheel and would very much like to fill it with a photometric V filter as you recommended. Could you recommend a filter manufacturer that has a high quality photometric V filter? My other filters are from Astrodon. I don't know if they offer the photometric V filter.
Ed,
I took a look at a 30 arcmin fov of BL cam and worry that the very bright star might bleed to much into your comps and or target.
I did go ahead and make a small sequence for GP And but the caveat with this is that it is bright at around 10.6 V with about a two hour period but a change of ~.6V,
Also Charts... I would anticiapte that you want East on the left with North Up (depending upon your CCD position-if North up does not work then turn the chart upside down and check that way to see if in the fuutre you want South up).
If you have problems getting a chart to print then please email me direct.
Tim
Will do. Thanks Tim.
AstroDon makes a good Johnson V filter.
Phil
Great. Thanks.
Your BL Cam chart shows the comp star sequence for visual observers which is given in tenths of a magnitude (without the decimal point). It's probably safe to assume that the visual comp stars are not (known) variables.
If a CCD squence were available for this star you would still see the comp stars in the finder chart shown to tenths of a magnitude, but if in the "Plot a finder chart or a table of field photometry?" option in VSP you pick "Photometry" you'll get a table with the comp star magnitudes shown to three decimal places (millimags). This star doesn't currently have a CCD sequence.
Your chart has north down and east to the right. This is the "inverted" orientation, what you would see in a newtonian (also a refractor or cassegrain without a diagonal). If you specify a CCD finder chart in VSP you'll get a "correct" image, north up and east left. Since you're using a german equatorial mount with your CCD you may see either a correct or inverted image on your screen depending on how your camera is oriented on the scope and which side of the telescope pier you're observing from.
Earlier in this topic Tim gave a link to the Help Guide for VSP. You can get more information on chart making there.
If, to get started, you just want to make a light curve for this star you don't really need a CCD sequence. You could just pick one of the visual sequence stars as a "comp" (C) and another as a "check" (K), then plot the differences in magnitudes (V-C and K-C) on the y axis and plot time on the x axis. The V-C points will show you the light curve. The K-C points should be constant. The scatter in the K-C points will give you an idea about the precision of your measurements.
If you have the "Handbook of Astronomical Image Processing" (Berry and Burnell), you'll find a tutorial there on how to do this. You should also be reading the AAVSO CCD Photometry Guide:
https://www.aavso.org/ccd-photometry-gude (sic)
If you decide to pursue CCD photometry I'd suggest you take the CCD Photometry on-line (CHOICE) course offered by the AAVSO which will probably be given in the spring.
Phil
Thanks Phil. That is a tremendous help.
Ed
When I as starting I did not measure variables at all. I measured stardard stars of know magnitude playing the game of using other standards as comparison and check. Landolt fields are good for that exercise. You could also use fields like NGC 7790 (now well-placed). The benefit is that you "know" if you are improving as the magnitudes of these stars are known for particular filters within specified errors. As you gain confidence, then try well reported Miras and compare your results with others. One hurdle is filters, most of us use Johnson and Cousins photometric filters.
Ed
Tim (CTX) just pointed out to me that BL Cam has a very nice photometry sequence. ... my mistake.
Phil
Tim (CTX) just pointed out to me that BL Cam has a very nice photometry sequence. ... my mistake.
Phil