Sep 04, 2008 UT: Photometry of new dwarf nova in Andromeda (short run in poor conditions)

Michael Richmond
Sep 04, 2008

On the night of September 3/4, 2008, I observed a new object -- a dwarf nova? -- which was recently discovered in the constellation Andromeda. 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

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 reference star is the one marked "A" in the chart above, which appears at differential magnitude 0.0. The star "B", at mag 0.9, shows an elevated level of scatter; I'm not sure why.

The floor of this diagram corresponds to a scatter of about 0.004 mag, but that's artificially small due to the single bright reference star. Nova And 2008 appears at differential magnitude 2.84; its scatter of 0.053 magnitudes is just the same as other stars of similar brightness. This is due to the large scatter in the measurements of _all_ the stars when I was looking at high airmass.

Light curves for selected stars (Nova And 2008 and stars A - D) in the field are shown below. Nova And 2008 is shown by light green crosses.

Here's a closeup of the variation in Nova And 2008 and a few comparison stars, which I have shifted for easy comparison. The data is too noisy to say much about the star. The one firm conclusion is that the target is fainter tonight (in unfiltered light) than it was last night (in V-band), by about 0.5 magnitudes.

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 "A" in my chart, TYC 2828 1694 1, has value 11.143. Remember these are unfiltered measurements.

Here's the start of the table.

# Measurements of NovaAnd2008 made at RIT Obs, Sep 4, 2008 UT. 
# by Michael Richmond under poor 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 2828-1694-1 mag=11.143 
#    to match value in Tycho-2 catalog. 
# UT day      JD-2,450,000  HJD-2,450,000   mag    uncert
Sep04.02462     2454713.52462  2454713.51984  14.027  0.063 
Sep04.02508     2454713.52508  2454713.52030  14.102  0.067 
Sep04.02552     2454713.52552  2454713.52074  14.052  0.064 

Last modified 9/04/2008 by MWR.