star catalogue

[tilvi]

Heres a sample of light curve of raw data for a perticular star and the corresponding data file.

http://www.phy.mtu.edu/~vpshetti/nsl/hd127762.jpg

the data file
http://www.phy.mtu.edu/~vpshetti/nsl/hd127762.dat

[tilvi]

Plots of a star (under observation) and a reference star. And the ratio of the above two.


http://www.phy.mtu.edu/~vpshetti/nsl/hd127762.jpg

The output data file.
http://www.phy.mtu.edu/~vpshetti/nsl/hd127762.dat

[tilvi]

Heres a plot comparing the canonical frames and the observed frames (for a perticular night).
NB: Canonical frame is the one which is taken during the same sidereal time as that of a star under observation.

http://www.phy.mtu.edu/~vpshetti/nsl/85eatuma.htm

Its little surprising that the observed and the canonical plots shows almost the same trends, even follows the small peaks. Also to note that the sigma does fall off to much lower values.

any thoughts?

Tilvi

[tilvi]

Here is a plot showing the canonical and the observed data.

http://www.phy.mtu.edu/~vpshetti/nsl/85eatuma1.htm

We expect that the two lines should match since both are at the same sidereal time.

Its little surprising that the two data sets, coincides in the begining and then deviates farther apart.

One possible problem might be with the CCD's sensitivity. The sensitivity is probably changing(?) with time.

Another possible reason might be thin clouds, which are invisible to naked eyes, but probably detected by the CCDs.

Thoughts (?).

FITS files are linked through the arrows.
Also included are the pixel locations for this star (on the FITS files indicated by arrows)

[tilvi]

I think, this might be one of the ways (?) to generate the star catalogue. We can continously append the data for a perticular star as we get good photometry data from NSL.
Heres how it might look like.

http://www.phy.mtu.edu/~vpshetti/nsl/hd127762-1.jpg and the corresponding data file http://www.phy.mtu.edu/~vpshetti/nsl/hd127762-1.dat

And appending the following nights data to the above:
http://www.phy.mtu.edu/~vpshetti/nsl/hd127762-2.jpg and the corresponding data file http://www.phy.mtu.edu/~vpshetti/nsl/hd127762-2.dat

suggestions?

[Vic Muzzin]

This seems like a great idea, the genius is in it's simplicity. This could be a quick way to build up a database of CONCAM information on stars. I am wondering if you have tried to include any 20 sec exposure in your data? Would the ratio stay the same on a 20 sec exposure? For some reason it still bothers me that half of our images are not used because of the moon.

[RJN]

The reason that Eta Ursa Majoris appears to change its brightness is surely not related to the star itself. Nearby stars show the same dimming, leading one to beleive that although the frame appears clear, some sort of haze layer has set in. Alternatively, the CCD did something strange and unexpected.

There is at least one other case of an anomalous photometric dropout, an older case involving Polaris found by undergraduate student Matt Merlo. Tilvi has promised to investigate this and post the data so that we can try to figure out the cause there. Understanding unusual photometric activity is important so that local instrumental variability can be discerned from atmospheric opacity changes and real stellar variability. And these cases make interesting puzzles!

- RJN

[nbrosch]

It is VERY difficult to do absolute photometry. Every little bit of atmospheric and instrumental influence works against this. We find that with a telescope and CCD we can do relative photometry with ~0.05 accuracy. For this, we compare the instrumental magnitude of the target with that of a few neighboring stars. Regarding the CONCAM photometry, I am also worried that there is no "flat fielding" done on the images, It seems to me that objects low in the sky would be dimmed by having the image formed by a lens that is effectively smaller than actual (projection).

Noah Brosch

[tilvi]

Here are some plots for constellation Cassiopeia (Cas).
The reference star is alpha cas (which is considered to be a constant star) and the stars under observations are Bet, gam & Del Cas.
Although Bet Cas is variable with 0.1d period with just less than 0.1 magnitude variability, I guess NSL photometry doesn't shows the variability.
a good reference for stars is at http://www.alcyone.de

Below are the light curves for the above stars for one night and again for 3 consecutive nights at CI station. And the ratio is just the logarithmic ratio i.e. log (star)/ log (ref. star)

http://www.phy.mtu.edu/~vpshetti/nsl/hd432-1.jpg
http://www.phy.mtu.edu/~vpshetti/nsl/hd432-1.dat

http://www.phy.mtu.edu/~vpshetti/nsl/hd5394-1.jpg
http://www.phy.mtu.edu/~vpshetti/nsl/hd432-1.dat

http://www.phy.mtu.edu/~vpshetti/nsl/hd8538-1.jpg
http://www.phy.mtu.edu/~vpshetti/nsl/hd8538-1.dat


For 3 consecutive nights.

http://www.phy.mtu.edu/~vpshetti/nsl/hd432.jpg
http://www.phy.mtu.edu/~vpshetti/nsl/hd432.dat

http://www.phy.mtu.edu/~vpshetti/nsl/hd5394.jpg
http://www.phy.mtu.edu/~vpshetti/nsl/hd432.dat

http://www.phy.mtu.edu/~vpshetti/nsl/hd8538.jpg
http://www.phy.mtu.edu/~vpshetti/nsl/hd8538.dat

I have not plotted the error bars, though the error values are included in the .dat files.

Another thing to try might be to find the minimum variability detected for stars with NSL data as Dr Nemiroff suggested.

thoughts?

[nbrosch]

Tilvi, I suggest to use additional data sets from other CONCAMs that would fill in the time gaps in your measurements. This would allow you to check whether the ratios you plot are valid for all cameras. I also suggest to concentrate on a star that has a well known strong variability (Algol, for example) and see whether it is possible to "discover" this before going on to find new results.

Noah Brosch

[tilvi]

Tilvi, I suggest to use additional data sets from other CONCAMs that would fill in the time gaps in your measurements. This would allow you to check whether the ratios you plot are valid for all cameras. I also suggest to concentrate on a star that has a well known strong variability (Algol, for example) and see whether it is possible to "discover" this before going on to find new results.

Noah Brosch

Dr Noah
Infact we did some preliminary analysis on Spica(Alp Vir). And it does show the variability. Infact this star saturates for MK & SA when it is at maxima. Ofcourse this is a bright star (0.98mag) with variable period of 4.01d

http://alcyone.de/cgi-bin/search.pl?object=HR5056

I will post some of the plots for this star soon.

Unfortunately, we donot have data for most of the stars for cross checking at the two stations simultaneously. At this point of time only CI seems to track the stars well while MK, although gives the data, but doesn't track stars very well. Let me see if I can get some stars at CI & MK for the same time to compare with.

[nbrosch]

Tilvi, Algol (beta Per) would be a much better target because it is not so bright, and the variability amplitude is much larger. Algol varies between 2.2 and 3.5, the eclipses are deep with a period of 68 hours and 49 minutes and the width of the primary eclipse is about 8 hours.

NoahBrosch

[lior]

Tilvi, Algol (beta Per) would be a much better target because it is not so bright, and the variability amplitude is much larger. Algol varies between 2.2 and 3.5, the eclipses are deep with a period of 68 hours and 49 minutes and the width of the primary eclipse is about 8 hours.

NoahBrosch

It is also closer to the north star. I think it will increase its availability for cross-checking by two different stations.

[tilvi]

Tilvi, Algol (beta Per) would be a much better target because it is not so bright, and the variability amplitude is much larger. Algol varies between 2.2 and 3.5, the eclipses are deep with a period of 68 hours and 49 minutes and the width of the primary eclipse is about 8 hours. Alp Per is used as check star.

NoahBrosch

Dr Noah
I just tried plotting for Algol (Bet Per) to see the variability detected by CONCAM. But I suppose that although its variable and has period of 2.8 days, this eclipsing period only comes once in 18(?) years.
Ref: http://www.alcyone.de/cgi-bin/search.pl?object=HR0936

Heres the plot (for CI) on 20-24 August, 04.
http://www.phy.mtu.edu/~vpshetti/nsl/hd19356.jpg

[nbrosch]

Tilvi, the variability of Algol is permanent and the repeatability of eclipses is like that of a Swiss watch. Algol is a good target for beginning observers of variable stars because it is so reliable. You can find some information in the special entry AAVSO has on it at http://www.aavso.org/vstar/vsots/0199.shtml and a set of comparison stars in the AAVSO chart at http://www.aavso.org/images/Betaper-aa.gif. The map has the magnitudes of each comparison star in tenths of a magnitude, underlined, next to the star name. To increse accuracy, you may want to compare Beta Per against a number of comparison stars. My guess re your results, in particular the ratios, is that you did not catch a minimum. This lasts only 8/68=12% of the period; if you consider the continuous coverage that a combination of CONCAMs would offer, you should see one minimum every ~3 days.

Good luck,
Noah Brosch

[Vic Muzzin]

Tilvi, I found a place to post my graphs, unfortunately they lost too much quality when posted. I think it happened when I converted the image to jpeg, anyway I should have the graph of Bet Lyr posted soon.

I think that the eclipse of Bet Per may be happening at times when the CONCAM is off. If you don't mind, I would like to work on Bet Per, I thought about looking at it before I started Bet Lyr. Lior suggested looking at a whole year of files, so that eventually we would catch an eclipse. I think the best way to work systematically to catch Bet Per "in the act" is to work backwards from last nights images until we find something of interest.

[nbrosch]

Vic, I think your idea of doing some systematic work on beta Per is very good. You may want to check the following sites:
http://www.as.ap.krakow.pl/o-c/data/get ... BETA%20per and, in particular http://www.as.wsp.krakow.pl/minicalc/PERBETA.HTM which gives the times of recent minima. A nice small paper on this system, including another way of calculating times of minima, is at http://www.physics.sfasu.edu/astro/betalyra/

Good luck,
Noah Brosch

[Vic Muzzin]

Thanks Noah!
Do you know of a listing that goes further back than that one? I am looking at two drops in Beta Persei (2453245.71 and 2453242.74). they are about 2.97 days apart.
Crap, i'm late for class, more later.

[Vic Muzzin]

Ok, I am back, and I just remembered about that wonderful thing called subtraction! The first date listed for an eclipse on link provided by Noah is 2453251.3899. Which, with a period of 2.8673, indicates there was an eclipse at 2453245.6553. I believe I caught the end of it at 2453245.7026. The previous eclipse should have occured at 2453242.7880, my last count for that day is at 2453242.7382 and shows a falling ratio.
Tilvi, I sent you the graph, if you can post it for me that would be great! Just make sure you give me the credit, unless it is a big mistake, then you can have the credit.


Heres the plot showing Bet Persei.
credits: Vic Muzzin. good spirit.
http://www.phy.mtu.edu/~vpshetti/nsl/betapersei2.htm

[nbrosch]

Vic, here is a "good practice" advice. Whenever you plot a graph, make sure you put in the units of both axes. In case of CONCAM photometry, I suggest to always look at intensity ratios (magnitude differences) between your target and a nearby comparison star. To convince your readers that what you see is real, display the (target-comparison) magnitude differences along witha similar magnitude differences' plot of another nearby star to the first comparison star.

Regarding actual photometry data, go to http://www.aavso.org/ and type "beta per" in upper left window.

Noah Brosch