Introduction

The CCD target list was developed to provide people who were new to the field of CCD photometry of variable stars with some interesting targets to which they could turn their CCDs, whilst developing their techniques.  I have listed below some projects and some stars, which comprise the new CCD target list, and I would be delighted to hear from anyone who decides to have a go!

There are two main aims of the CCD target list:

• 1. To encourage people who have CCD cameras, and who have developed the ability to take reasonable images with them, to point them at Variable Stars and develop their photometry techniques

• 2. To provide some interesting targets and projects to get people involved in doing some real science

Charts and comparison star sequences can be downloaded from the AAVSO Variable Star Plotter.

Beginner’s Category

The Beginners Category contains eclipsing binaries which show significant brightness changes over a reasonable time scale. These stars are guaranteed to vary! Following one or more of these stars over a few nights allows the beginner to test their photometric system and see some results in a relatively short period.  The CCD mentoring scheme also puts beginners in touch with more experienced observers. If you would like to be allocated a mentor, contact the VSS Director.

                                                     Table 1: Eclipsing binaries in the beginner’s category

Some variable star observers are using Digital SLR cameras for photometry of brighter targets. Further information on this approach, especially how they maybe used in the study of eclipsing binaries, can be obtained from the VSS Eclipsing Binary Secretary, Des Loughney.

Basic CCD Data

Dwarf novae (DNe) show outbursts during which they increase in brightness by two magnitudes and often much more; the shortest outburst duration is two to three days. However recent CCD monitoring of certain infrequently outbursting DNe has revealed that several stars appear to show intriguing “brief outbursts”. These are much smaller in magnitude (often only 1 mag) and in duration (often only 24 h). The Basic CCD Data project involves the long term monitoring of DNe which are thought to exhibit these brief outbursts, with the aim of determining how frequently they occur, whether there is a periodicity and whether they are in any way associated with true outbursts.
Who knows what new science this may reveal?

At its simplest, this project involves taking one image of the DN every clear night and measuring the brightness. Many of the targets are very faint at quiescence, so the target may actually be invisible on the image. If VS photometry is not your main interest, you could even consider following one or two of the targets, taking a few images during the course of your normal observing programme. Given the short duration of the outbursts, the key here is to image as often as possible. Two of the stars go into outburst very frequently: V1316 Cyg every couple of weeks or so and V452 Cas about once a month. Observing these stars for a few weeks more or less guarantees the new observer to experience the delights of spotting an ourburst!

                                                                           Table 2: Basic CCD target stars

Time resolved photometry

Time resolved photometry is a technique commonly used in the monitoring of variable stars, especially cataclysmic variables. Again the technique is relatively simple: a series of images of the target is taken over a period of minutes or hours to look for variations in brightness. Sometimes this technique is referred to as “time series photometry”. Cataclysmic Variables (CVs), DNe especially, can show variations over many times scales and sometimes these are associated with orbital features of the binary system which makes up the CV. The technique is often applied to newly discovered CVs during outburst, with the aim of detecting orbital humps or superhumps. The length of exposure depends on the brightness of the star and the size of the telescope, among other things.

How does one know which CV’s are worth following up with time resolved photometry? Well, outbursts of some of the stars on the VSS Cataclysmic and Eruptive Variable Star Programme (see below) merit follow–up. In addition, detections of outbursts of potentially interesting CVs are posted by their discoverers on a number of user groups including the BAA VSS alert group, which all members of the VSS are encouraged to join.

Another good resource on CV’s in outburst is the CVnet- Cataclysmic Variable Network. 

In addition, the Center for Backyard Astrophysics (CBA), coordinated by Prof. Joe Patterson at Columbia University, NY, USA, runs regular campaigns on a variety of CVs. 

Other targets and projects

Once the CCD photometry bug has bitten, there are of course thousands of other targets which could be monitored. A good place to start is the BAA VSS Cataclysmic and Eruptive Variable Star Programme. Monitoring for outbursts of poorly charactrised eruptive stars and follow up with time resolved photometry is useful. Many of these stars are very faint at quiescence and are probably undetected by most amateur CCD systems – that is until they go into outburst. Be warned, though: detecting a rare outburst in one of these stars may mean you become hooked!

Other resources

BAA VSS Web site 

The AAVSO produces several guides including one on CCD photometry and one on DSLR photometry. 

AAVSO suggested stars for CCD observers  

CCD target list, 4th edition. 5 January 2019