CCD Photometry Mentor Project

August 2007
Jeff Hopkins
Hopkins Phoenix Observatory
7812 West Clayton Drive
Phoenix, AZ 85033-2439
phxjeff@hposoft.com

Many observers have CCD cameras and have desired to try something beyond taking pretty pictures. Photometry is an area that holds much potential for astronomical CCD work. Getting started can be daunting.

The July 2007 issue of Sky & Telescope magazine had a two page article on the fast binary star system SZ Herculis. Where there are many visual observations of this system, there are not many photometry observations. This may be a good project to get started with CCD photometry.

To start, unfiltered or filtered photometry without calibration can be done to produce a light curve. Once successfully completing that phase, the system can be calibrated and filter photometry can be done. Having gone through this project, more advanced projects should be easy.

Other objective can be:

Calibrating other comparison stars
Determining best exposure times
Determining best aperture and annulus sizes

The following information should help get started.

SZ Herculis

Image taken at HPO 9 August 2007. Observatory temperature at 21:30 was 102 F. Image was taken with a modified DSI Pro (TEC cooled), F/10 12" LX200 GPS with F/3.3 focal reducer and V photometric filter. Exposure was 10-8 second exposures stacked with dark frames subtracted, No flat fielding was done.

RA (2000) 17:39:36.8
Dec (2000) +32:56:47
Spectral types: Ao + G2
Other IDs: AAVSO 1735+33, HIP 86430, AN 174.1908, NSVS 8048731


Algol type eclipsing binary star system
Visual magnitude 10.2 to 12.0. B= ?, R= ?. I= ?
Period 0.81809828 days (19h 38m 0.0615232 s)
Epoch: 30 July 1973 (HJD 2441864.3052 AAVSO)
Ingress: 90 minutes Egress: 90 minutes Total eclipse 180 minutes

Possible Comparison Stars

References:
IBVS 2792, IBVS 5467
Sky & Telescope July 2007 (Pages 58, 59) and June 1997 (Pages 76, 77)

To Do:

Check data
Find new references
Determine comparison stars and magnitudes
Find star system and obtain images (filtered or non-filtered)
Process images and obtain instrumental magnitudes - plot data
Calibrated system, take filtered data, reduce data, plot calibrated filtered data


To help with finding the star the AAVSO has a very nice star chart plotting program. It can be found at

http://www.aavso.org/observing/charts/vsp/

The following is a screen shot of the window that allows you to create your own customized star chart.

 

With this program you can enter the star of interest name
(e.g., SZ Her),

Select the Scale of the chart:

B & BR = 180 arc minutes
C & CR = 90'
D & DR= 60'
E & ER = 30'
F & FR= 15'
G & GR= 7.5'

The FOV
Resolution and Magnitude Limit will be added automatically.

You can select the orientation of the chart
(North up or down and East right or left).

Selecting the "Use DSS Image" will create an actual photo of the area. This is good for up to 60 arc minutes FOV. Beyond that you cannot use an image, but instead a printed plot of the star field is generated. There are other things that can be set up also.

To make the best use of this take some images of easy objects with your telescope and CCD camera and any focal reducer used. Get an idea of the the scale of the image and orientations. Then generate star charts with that orientation and FOV of 180', 60', 30' , 15' and 7.5'. This will give you a good set of charts for finding the SZ Her and comparison stars. Below are five charts with FOV 180' to 7.5' with North up and East left. Click on the chart for the full-sized image.

 

60' Field

30' Field

180' Field

15' Field

7.5' Field

 

 

 


Timing information
Precise timing for SZ Her is important. See how AutoStar determine the time for the FITS Header and how a more precise time can be calculated.


DSI Pro Linearity Check
To do accurate photometry the CCD camera must produce a inear output over the range of ADU counts reported


DSI Pro TEC Cooling
Using the added TEC,heat sink and fan, the DSI Pro case is cooled with the maximum cooling directly over the cold finger. To see a graph of the effect versus time click the above link. The ADU count is the count provided above the Histogram.


Image Analysis
On 9 August 2007 BVRI images were taken and used for preliminary data for setting up an observing program for SZ Herculis.


Trouble Shooting
Just getting started and can't get an image, maybe this will help.


DSI Camera Modification
Ready to take things to the next level? Check out a simple modification for cooling the DSI camera.

For monochrome DSI cameras it is highly recommended you replace the nose piece face plate with a low profile one and add a shutter/dark slide (~$75). You can screw a filter into the nose piece (e.g., am IR blocking filer or V photometric filter). For multiple filters a filter wheel is strongly suggested. ATIK is a reasonably priced ($199) manual filter wheel that is well made and works well. These items can be purchased from ScopeStuff at http://www.scopestuff.com/ Some of the items are temporally out of stock, but keep checking as more should be arriving shortly. For photometric filters AstroDon has a reasonably price set of good filters (1.25" BVRI set $300). See http://www.astrodon.com/products/product.cfm?CatID=4


DSI Photometry Certification Project

A Certification Program has been set up


AutoStar CCD Photometry Book
There are a few copies left.


If you are interested in this project, please e-mail me. There are already several people interested. The goal is to obtain good photometric data so a light curve can be generated. Any CCD camera can be used. Filters are not needed, but will enhance the data. I will post questions and answers and any images that are sent me.


Created 28 July 2007
Modified 30 August 2007