Skip to main content

DSLR photometry of V342 Cen do I need B-V?

Due to the New England winter storm currently affecting the area, phone coverage at the AAVSO may be much reduced until Wednesday. The staff is still available via email, and we suggest using that method to contact us if you need assistance.
Carl Knight's picture
Carl Knight
Offline
Joined: 2010-08-27

I am using Iris to do DSLR photometry of V342 Cen.

I have 21 x 30s images of V342 Cen and its comparison stars. I have stacked these in lots of 7 images. I am processing the green channel from each stack. There is general agreement between the resulting green channel images for the instrumental magnitudes of the comparisons and target.

I am using the Reduction Beginners spreadsheet from the Citizen Sky project.

Do I need to provide a B-V value for V342 Cen itself? Entering a value in the spreadsheet there (i.e. I make one up just to see the results) makes a significant difference to the resulting calculated magnitude for V342 Cen itself. If a B-V value is required, where can I obtain one from? VSX does and the photometry table for V342 Cen do not provide one.

I presume as V342 Cen is a classic CV (UG according to VSX) that B-V will vary with orbital period depending upon which components spectra is dominating - Correct?

Cheers.

- Carl.

V0342 Cen color
Sebastian Otero's picture
Sebastian Otero
Offline
Joined: 2010-09-19

There are two observations in APASS:

2455611.55385 V= 15.1621 (0.081); 2455611.55436 B= 15.2313 (0.076); B-V= 0.07
2455662.60873 V= 15.8463 (0.068); 2455662.60925 B= 16.1658 (0.059); B-V= 0.32

Best wishes,
Sebastian

Additional color photometry
Sebastian Otero's picture
Sebastian Otero
Offline
Joined: 2010-09-19


And this photometry is taken from 1997A&AS..124...55C:

V= 15.47; U-B= -0.61; B-V= 0.14; V-Rc= 0.37; Rc-Ic= 0.32

CVs and B-V for data reduction...
Carl Knight's picture
Carl Knight
Offline
Joined: 2010-08-27

Hi Sebastian,

Thanks for the data.

A follow up and more general question(s) (for you or anyone who knows) is:

I expect B-V to be changing as the components orbit. Are the values you have quoted some sort of average or a snapshot? I suspect the latter.

When doing data reduction of CVs is the B-V of the variable even used in the manner intended in the CS Reduction Beginners spreadsheet?

Thanks.

- Carl.

AAVSO 49 Bay State Rd. Cambridge, MA 02138 aavso@aavso.org 617-354-0484