AM Thursday July 24, 2014 - First Variable Star Estimate This Year

  After several warm, humid, and hazy / foggy nights that were useless for doing any kind of amateur astronomy, we had some stormy weather on Wednesday morning the 23rd and a cold front moved in behind them with milder and drier air. Cloud cover for the rest of Wednesday kept the ground from drying out, I was at work until after midnight. When I was driving home from Greensburg to Indianapolis I ran into some surprisingly thick but brief low fog banks on the Interstate and the back roads. The sky was clearing out, the air was cooling, and the moisture from the rain storms was condensing near the ground in places.

  I was home by 2:30 AM Thursday, and things still didn't look promising for doing any observing. There were alto-cumulus clouds drifting across the sky from the north to the south, with stars visible in the gaps between them. At least there wasn't much fog around in my neighborhood. My plan had been to do a Meteor Watch, but I needed at least an hour of clear sky to do an IMO report. By 4:00 AM the sky was still mostly cloud-covered, with only about an hour to go until the start of dawn. That made this night "a wash" as far as the meteors went. This was also a shame because there was no moonlight interference tonight. The thin Waning Crescent Moon wasn't due to rise until the start of dawn.

  However, by 4:15 AM it looked like the clouds were finally starting to move out, and I had a backup plan in mind. There was an Eclipsing Binary Star that I'd found out about over the weekend, that was bright enough for binocular viewing. I got the 16x50 binoculars out, mounted them on the camera tripod, and took them out to the patio. I sat in a deck chair and tilted up the tripod looking east. Dawn was still half an hour away, and this star had just risen high enough to clear the roof of our house. I had the charts for it next to me, printed out over the weekend. This was actually my first variable star estimate of the year (though I'm a little embarrassed to write that!).

  At 4:34 AM (8:34 UT July 24) I estimated V1268 Tauri as 7.0 magnitude. I used the stars TYC 1811-1548-1 (approximately 6.9 V magnitude) and TYC 1811-1859-1 (approximately 7.4 V magnitude) as comparison stars. V1268 Tau was just slightly dimmer than the 6.9 star but much brighter than the 7.4 star. I think my error is easily plus or minus 0.1 magnitude. The binocular limit was 10.0 mag. or better and the naked eye limit was 5.1 where it was cloud-free (by this time most of the altocumulus had moved south of me and this part of the sky was very clear. The elevation of the star was 30 degrees east.

  This EA-type Eclipsing Binary has a period of 8.161235 days (8 days 3 hours 52 minutes) and it wasn't predicted to be in eclipse tonight, but I wanted to get an idea of how bright it was out of eclipse. The VSX site that I use lists the range as 7.42 - 8.62 V mag. What's interesting about this, however, is that the AAVSO Database has only 17 estimates in it from two observers, and all of the estimates show it brighter than the maximum given. One observer made 14 visual estimates of V1268 Tauri from late September to late October 2005. All of them were 6.9 - 7.0 magnitude. A second observer made three CCD or Photometric estimates from the end of December 2010 to early January 2011. All of these were also close to 6.9 magnitude. I wonder how the listed brightness range and period were generated? Also interesting; there's no eclipse duration listed in VSX, so I'm not sure how much time the fall and rise in brightness takes. This makes this star well worth observing in the future!

  The next predicted eclipse for V1268 Tauri is 2:57 UT July 29, or 10:57 PM EDT on Monday, July 28. If skies are clear next Tuesday morning I'm going to try to make another estimate of it and see if the prediction is accurate. Here's the finder chart I printed using the AAVSO's VSP tool online. V1268 Tauri is very easy to find since it lies between Zeta Persei (the bright star at the top of the chart) and the Pleiades Cluster (shown near the bottom).