PM Sat. January 28th - AM Sunday January 29th, 2012 - RR Leonis Observations

  Indianapolis was between two "clipper systems" on Saturday evening, January 28th. Skies were clear at sunset and dusk. I've been meaning to try making visual brightness estimates for large amplitude RR Lyrae stars for the past couple of months, and a link from the AAVSO web site predicted a peak for the RRab-type star RR Leonis at 11:30 PM local time.

  RR Lyrae variables are characterized by rapid cycles of brightening and dimming. Most of them go through a cycle in about half a day and have a range of about one magnitude. RR Leonis is easy to find since it's only a couple of degrees west of the fairly bright star Zeta Leonis in the "Sickle of Leo." This star has a period of 0.4523999 days (10 hours, 51 minutes, and 27.35 seconds) and ranges between 9.9 - 11.3 V magnitude. It should have shown a quick rise from a fairly faint star in my 10" telescope to an easy to see star in about 90 minutes. Visual estimates of this type of variable are often frowned upon by professional astronomers. They prefer CCD imaging, which is much more accurate. However, I'd also recently read through email lists that a lot of these stars go for months with no CCD brightness measurements and that visual observers like me can fill in some "gaps" with the data for RR Lyr stars. This caught my interest and this was my first chance to see if I could contribute any useful data to the AAVSO. 

  Conditions outside tonight weren't terrible for late January but they weren't too comfortable either! It was very clear at the start of my session but more and more high clouds started to drift in from the north as the night went on. The Waxing Crescent Moon was low in the west and set around 11:35 PM so there wasn't much moonlight interference. Temperatures were at the freezing point or just below it, but there was a steady breeze from the southwest. This added a wind chill that felt about ten degrees colder than the air temperature! There were thin patches of snow here and there on the grass in the back yard. I was bundled up as much as possible and I also had hand-warmers tucked into my gloves, but I had to take breaks every now and then to go back in the house and warm up. I also had to drag out the patio table umbrella tonight and leave it half open to block light from our neighbors' porch lamp to my south, which seems to burn all night and day!

  I had the 10" f/4 telescope set up on the back patio by 9:45 PM and started observing RR Leonis just after 10:00 PM. At first I thought that it wasn't going to get as bright as I thought from the amplitude that had been listed for it. Between 10:00 PM and just before midnight I only noticed it getting about 0.3 magnitude brighter. I also wondered if I'd mis-read the prediction table. 11:30 PM was the rough time that RR Leonis was supposed to reach its brightest point, but that time came and went with very little change observed. 

  I took a break inside the house for half an hour, and when I went back out to look at RR Leonis through the telescope I had a jaw-dropping surprise. Sometime during that half hour between almost midnight and 12:26 AM, the star had surged in brightness. I was now seeing it clearly brighter than the nearby 10.4 magnitude comparison star on the chart, and for the two hours before midnight it had always been noticeably dimmer than this star. I checked and double-checked, but there was no doubt in my mind about this. The prediction on the web site link must have been off by an hour. 

  I'd wanted to keep watching RR Leonis for a couple of hours as it got dimmer, so I could pin-point a time of peak brightness, but cirrus clouds were starting to cover the area and thick clouds soon moved in all over the sky. Soon after 12:30 AM I had to give up and haul the telescope back inside. 

  Sunday afternoon, I reported the 12 estimates made for RR Leonis to the AAVSO website. I also graphed them out to see if they made any sense. Even though this session was cut short by clouds, I found out that visual brightness estimates for some RRab stars are not only possible, but they might also prove valuable to refine predictions for peak brightness times. 

  TABLE OF ESTIMATES MADE TONIGHT:
 
  RR LEONIS / 000-BBR-195 / 1002+24
  Type: RRAB / Spectral Type: A7 - F5 / Range: 9.9 - 11.3 V magnitude / Period: 0.4523999 days
(10 hrs 51 minutes 27.35 seconds)
  Chart Used = 6340SO (D scale) (Generated from AAVSO Web Site VSP on January 28th, 2012)
  Instrument / Power Used = 10” f/4 (102X)
  Instrument Limit = 13.0+ magnitude (until clouds moved in by 12:30 AM)
  Eye Limit = 4.6 magnitude (until clouds moved in by 12:30 AM)
  Reported to AAVSO = PM Sunday, January 29th, 2012
 
Time     Time/Date (UT)    Julian Day/Time    Mag.    Comp Stars/Notes    Elevation
10:09 PM    3:09 Jan. 29    245 5955.6313    10.9    Between 10.4 and 11.2 but slightly
closer to 11.2 in brightness.    35 E

10:16 PM    3:16 Jan. 29    245 5955.6361    10.8    Halfway between 10.4 and 11.2    35 E

10:25 PM    3:25 Jan. 29    245 5955.6424    10.8    Halfway between 10.4 and 11.2    40 E

10:34 PM    3:34 Jan. 29    245 5955.6486    10.7    Between 10.4 and 11.2 but slightly closer to 10.4 in brightness.    40 E

10:41 PM    3:41 Jan. 29    245 5955.6535    10.7    Between 10.4 and 11.2 but slightly closer to 10.4 in brightness.    40 E

10:54 PM    3:54 Jan. 29    245 5955.6625    10.7    Between 10.4 and 11.2 but slightly closer to 10.4 in brightness.    45 E

11:06 PM    4:06 Jan. 29    245 5955.6708    10.7    Between 10.4 and 11.2 but slightly closer to 10.4 in brightness.    45 E

11:18 PM    4:18 Jan. 29    245 5955.6792    10.6    Slightly but definitely dimmer than 10.4 and much brighter than 11.2    50 E

11:44 PM    4:44 Jan. 29    245 5955.6972    10.6    Slightly but definitely dimmer than 10.4 and much brighter than 11.2    55 ESE

11:54 PM    4:54 Jan. 29    245 5955.7042    10.6    Slightly but definitely dimmer than 10.4 and much brighter than 11.2    55 ESE

12:23 AM    5:23 Jan. 29    245 5955.7243    10.1    Between 9.9 and 10.4 but slightly closer to 9.9 in brightness.    60 ESE

12:35 AM    5:35 Jan. 29    245 5955.7326    10.0    Barely dimmer than 9.9 (almost equal) and much brighter than 10.4. Used Code “U” and wrote “Cirrus Clouds” when I reported this.    60 ESE