Sep 11, 2008 UT: Photometry of new dwarf nova in Andromeda = V466 And

Michael Richmond
Sep 11, 2008

On the night of September 10/11, 2008, I observed a new object which was recently discovered in the constellation Andromeda. The name of this variable has now been set to V466 And. It's still very early, but you can find a bit of information on the new object in these sources:

The object is at RA = 02:00:25.40 Dec = +44:10:18.7, so it rises just after sunset at this time of year. It is well placed for observations from the Northern Hemisphere.

The setup was:

Notes from the night

This is a chart of the field taken from the DSS.

The chart has several of the brighter stars in thefield labelled with letters, just to keep me straight as I perform the reductions. The star labelled "bright!" saturates my detector. Stars A and B are in the Tycho-2 catalog,

label                         RA        Dec          Bt        Vt         
  A    TYC 2828 1694 1     29.97369  +44.10297       12.081  11.143
  B    TYC 2841  810 1     30.22008  +44.08782       13.369  11.679

                    These stars appear in AAVSO VSP chart      V
  P                                                           14.2
  Q                                                           14.1
  R                                                           13.0

On this night, star A was saturated as the field rose high above the horizon and I re-focused. Therefore, I don't include A as a reference in the ensemble, though I do show its measurements in the graphs below.

I measured the instrumental magnitude of each star with aperture photometry, using a radius of 3 pixels = 5.6 arcseconds and sky defined by an annulus around each star. Following the procedures outlined by Kent Honeycutt's article on inhomogeneous ensemble photometry, I used all stars available in each image to define a reference frame, and measured each star against this frame.

One output of the ensemble solution is the value of the zero-point of each frame relative to the others. In the graph below, I plot this zero-point as a function of time.

Below is a graph of the scatter in differential magnitude versus magnitude in the ensemble solution. The only good bright reference star is the one marked "B" in the chart above, which appears at differential magnitude 0.8. The stars with elevated scatter, such as "A" at differential mag 0.0, are not included in the solution as reference stars.

The floor of this diagram corresponds to a scatter of about 0.005 mag, but that's artificially small due to the single bright reference star. V466 And appears at differential magnitude 3.8; its scatter of 0.029 magnitudes is just the same as other stars of similar brightness.

Light curves for selected stars (V466 And and stars A - D, P, Q) in the field are shown below. V466 And is shown by light green crosses.

Here's a closeup of the variation in Nova And 2008 and a few comparison stars. The data is too noisy to say much about the star. I show the measurements (green dots) and a line representing a smoothed version of the measurements, using a boxcar of width 5 measurements (corresponding to about 2.3 minutes of time).

I don't see any real periodic signal in the light curve of V466 And down to a level of +/- 0.03 mag or so. Either the star has decreased the amplitude of its variations, or (more likely?) it has simply faded too far for our small telescope to measure adequately. Look at its behavior relative to other stars in the field over the period of our measurements:

I've made a table of the measurements themselves, with three different flavors of time. The differential magnitudes from the ensemble solution have been shifted so that star "B" in my chart, TYC 2841-810-1, has value 11.679. Remember these are unfiltered measurements.

Here's the start of the table.

# Measurements of V466_And made at RIT Obs, Sep 11, 2008 UT. 
# by Michael Richmond under good conditions. 
# Each exposure 30 seconds long with no filter. 
# Tabulated times are midexposure (FITS header time - half exposure length) 
#    and accurate only to +/- 1 second (??). 
# 'mag' is a differential magnitude based on ensemble photometry 
#    using a circular aperture of radius 5.6 arcseconds. 
#    which has been shifted so TYC 2841-810-1 mag=11.679 
#    to match Vt value in Tycho-2 catalog. 
# UT day      JD-2,450,000  HJD-2,450,000   mag    uncert
Sep11.01465     2454720.51465  2454720.50972  14.820  0.025 
Sep11.01558     2454720.51558  2454720.51065  14.704  0.022 
Sep11.01604     2454720.51604  2454720.51111  14.729  0.023 

Last modified 9/04/2008 by MWR.