Forum der Vereinigung der Sternfreunde

Hi,

we, some students (Master and Ph.D.) of the AIfA in Bonn, Germany, decided to join and provide photometric data.

Since this is the first time I'm participating in such a program, I have some questions and perhaps those of you with much more experience can help me. We have a 50cm Cassegrain telescope in the city of Bonn, a SBIG STL6303E camera and at the moment Baader RGB filters installed. Last night I took about 50 data points per object and filter (so about 450 in total) and was now checking the first results (done with MaxIm DL Pro 5).

It looks that the three reference stars are quite stable and our target (WR 134 in B filter) is variable (quite a lot). Furthermore there is an mag offset of about 0.6mag to the values of the VSP of AAVSO.

Before I continue with our data reduction, I wanted to hear your opinions.

Best,

Dominik

Dear Dominik:

Thanks for your interest ? this is great! When you say ?quite stable? can you give me an idea of the standard deviation about a constant level for the reference stars (hopefully non variable and of similar magnitude as the program star. If this is 0.5% (0.005 mag) or better per data point, then you are golden.

I should state that such observations will only be useful if taken in large number over as much as possible of each clear night and during as many different nights as possible. Can you also observe the other 2 WR stars, perhaps alternatingly? Do you have the possibility of a robotic mode to make life easier?

Viel Glueck und besten Dank!

Tony Moffat
(doctoral student at Univ. Bonn in 1966-69)

From: Dominik Klaes (fg-spek-convento@vds-astro.de)
Sent: Friday, July 12, 2013 8:10 PM
To: fg-spek-convento@vds-astro.de (fg-spek-convento@vds-astro.de)
Subject: [fg-spek] 50cm(==>)AIfA Bonn: First results




Hi,

we, some students (Master and Ph.D.) of the AIfA in Bonn, Germany, decided to join and provide photometric data.

Since this is the first time I'm participating in such a program, I have some questions and perhaps those of you with much more experience can help me. We have a 50cm Cassegrain telescope in the city of Bonn, a SBIG STL6303E camera and at the moment Baader RGB filters installed. Last night I took about 50 data points per object and filter (so about 450 in total) and was now checking the first results (done with MaxIm DL Pro 5).

It looks that the three reference stars are quite stable and our target (WR 134 in B filter) is variable (quite a lot). Furthermore there is an mag offset of about 0.6mag to the values of the VSP of AAVSO.

Before I continue with our data reduction, I wanted to hear your opinions.

Best,

Dominik

_________________
Tony Moffat

Hi Tony,

thanks for the fast reply!

So I checked the standard deviation of two reference stars (the third one is not saved by MaxIm, I don't know why):

Name Chart measured
000-BKZ-845: 10.218 +- 0.064 / 9.9290 +- 0.0015
000-BLB-382: 10.670 +- 0.022 / 11.6130 +- 0.0044

Taken from http://www.aavso.org/vsp/chart , chart field 12290BS .

This looks quite suspicious...


So yes, we are at the moment 4 interested observers (two master students, one PhD. student, one PostDoc) and we all live close to our institute so we should be able to observe those stars regularly (the biggest problem is the weather). Furtermore we could include a lab course in taking data so that should be our smallest problem.

I can include the 2 other WR stars, but we can observe them only until 23 UT (then airmass > 2). At the moment we I observe only the three WR stars alternatingly (WR 134 in B,G,R , then WR 135 in B,G,R and so on).

And yes we have a semi-robotic telescope. We still have to monitor it but taking images, changing filters and coordinate / object changes are scriptable (and this is what I've already done).

Thanks!

Dominik


Edit: MaxIm DL Pro 5 only saves the two brightest reference stars. That's the reason why I can't give you more info about the third one. But it looks quite the same.

Hallo Dominik!

You talk about RGB filters. I am no photometric expert but why don't you use a V (or even a B) filter? How do you combine them for V? Do you know the filter curves? Working just on the other River side in Bonn we should have a coffee together...

Tschüss, Thomas

Hi again Dominik:

I?m not sure what these numbers mean. What I was asking is the std dev of your observations, i.e. the empirical scatter around the empirical mean. E/g/ if you have n measures x_i, i = 1, n, then mean <x> = (Sum x_i)/n. Then std dev sigma = Sqrt{ [Sum (x_i ? <x>)^2]/(n-1)]}. Nothing really sophisticated. The important thing is to judge the quality of your photometry. This is best done on the difference in magnitude between a minimum of two reference stars of fairly similar magnitude (up to a difference of +/- a mag or so is OK) as the program star. One should also check for colour terms... (blue stars are more affected by extinction than red stars in broadband photometry).

Thanks, Tony

From: Dominik Klaes (fg-spek-convento@vds-astro.de)
Sent: Friday, July 12, 2013 9:31 PM
To: fg-spek-convento@vds-astro.de (fg-spek-convento@vds-astro.de)
Subject: [fg-spek] Re: 50cm(==>)AIfA Bonn: First results




Hi Tony,

thanks for the fast reply!

So I checked the standard deviation of two reference stars (the third one is not saved by MaxIm, I don't know why):

Name Chart measured
000-BKZ-845: 10.218 +- 0.064 / 9.9290 +- 0.0015
000-BLB-382: 10.670 +- 0.022 / 11.6130 +- 0.0044

Taken from http://www.aavso.org/vsp/chart , chart field 12290BS .

This looks quite suspicious...


So yes, we are at the moment 4 interested observers (two master students, one PhD. student, one PostDoc) and we all live close to our institute so we should be able to observe those stars regularly (the biggest problem is the weather). Furtermore we could include a lab course in taking data so that should be our smallest problem.

I can include the 2 other WR stars, but we can observe them only until 23 UT (then airmass > 2). At the moment we I observe only the three WR stars alternatingly (WR 134 in B,G,R , then WR 135 in B,G,R and so on).

And yes we have a semi-robotic telescope. We still have to monitor it but taking images, changing filters and coordinate / object changes are scriptable (and this is what I've already done).

Thanks!

Dominik

_________________
Tony Moffat

I think the data quality look good, but I am confused about the RGB mentioned here. In your email you sent, you said you would be using BVR filters. If it is BVR, it will be more useful than typical RGB filters used for making pretty pictures. Certainly a long, dense, time-series of WR 134 and 137 should be very interesting, but we'll probably see something interesting in WR 135 too (but likely a smaller amplitude).

Cheers,

Noel

Yes, this confusion came up yesterday evening. Someone changed the Johnson BVR filterset to Baader RGB without writing to our mailing list and changing it in our camera software. Hopefully in the next days that will be changed.

Update: So the filters were just changed, we can now observe with a complete UBVRI this night. I'll change the headers of the last images and will upload them again. Sorry for that confusion.

But it's good to know that the data quality is good enough!

Hi again Dominik:

Was this issue ever settled? I?d like to know.

Thanks, Tony

From: Tony Moffat (fg-spek-convento@vds-astro.de)
Sent: Saturday, July 13, 2013 9:30 AM
To: fg-spek-convento@vds-astro.de (fg-spek-convento@vds-astro.de)
Subject: [fg-spek] Re: 50cm(==>)AIfA Bonn: First results




Hi again Dominik:

I?m not sure what these numbers mean. What I was asking is the std dev of your observations, i.e. the empirical scatter around the empirical mean. E/g/ if you have n measures x_i, i = 1, n, then mean = (Sum x_i)/n. Then std dev sigma = Sqrt{ [Sum (x_i ? )^2]/(n-1)]}. Nothing really sophisticated. The important thing is to judge the quality of your photometry. This is best done on the difference in magnitude between a minimum of two reference stars of fairly similar magnitude (up to a difference of +/- a mag or so is OK) as the program star. One should also check for colour terms... (blue stars are more affected by extinction than red stars in broadband photometry).

Thanks, Tony

From: Dominik Klaes (fg-spek-convento(==>)vds-astro.de ([email]fg-spek-convento(==>)vds-astro.de[/email]))
Sent: Friday, July 12, 2013 9:31 PM
To: fg-spek-convento(==>)vds-astro.de ([email]fg-spek-convento(==>)vds-astro.de[/email]) (fg-spek-convento(==>)vds-astro.de ([email]fg-spek-convento(==>)vds-astro.de[/email]))
Subject: [fg-spek] Re: 50cm(==>)AIfA Bonn: First results




Hi Tony,

thanks for the fast reply!

So I checked the standard deviation of two reference stars (the third one is not saved by MaxIm, I don't know why):

Name Chart measured
000-BKZ-845: 10.218 +- 0.064 / 9.9290 +- 0.0015
000-BLB-382: 10.670 +- 0.022 / 11.6130 +- 0.0044

Taken from http://www.aavso.org/vsp/chart , chart field 12290BS .

This looks quite suspicious...


So yes, we are at the moment 4 interested observers (two master students, one PhD. student, one PostDoc) and we all live close to our institute so we should be able to observe those stars regularly (the biggest problem is the weather). Furtermore we could include a lab course in taking data so that should be our smallest problem.

I can include the 2 other WR stars, but we can observe them only until 23 UT (then airmass > 2). At the moment we I observe only the three WR stars alternatingly (WR 134 in B,G,R , then WR 135 in B,G,R and so on).

And yes we have a semi-robotic telescope. We still have to monitor it but taking images, changing filters and coordinate / object changes are scriptable (and this is what I've already done).

Thanks!

Dominik



Tony Moffat

_________________
Tony Moffat