The Virtual Telescope - Bellatrix Astronomical Observatory


	The extremely rare outburst of V455 And (formerly HS2331+3905) V455 And , imaged on Sept.5.9, 2007. The variable is the brightest star nar the center. On Sept. 4.775 H. Maehara (Japan) reported that the variable star HS 2331+3905 (now V455 And) was in outburst at mag. 14.6, for the first time since the discovery of its cataclysmic nature (2004). Hints were for a candidate of the rare and fashinating WZ Sge group. Over the following hours, it rises again and again. Once heard of that alert, I planned an observing session with the Virtual Telescope, using the main scope (C14-f/8 on Paramount ME + SBIG ST8-XME, NABG). On ept. 5, during the evening twilight, I slewed the telescope to the star, finding it VERY bright (brighter than mag 9.0). I started time-resolved photometry and real-time data reduction. Soon, I realized that the star was near its maximum and humping. I was able to cover the star for about 9 hours, under excellent sky conditions. I observed unfiltered, to keep th eintegration time as short as possible (10 seconds). The resulting lightcurve was amazing. (Click on the plot to get the full-res graph) The star showed a very complex modulation: larger ones (0.4 mags in full amplitude), with smaller and faster ones. PDM period analysis provided a period candidate of 1.35 +/- 0.05 h 81 minutes), consistent with the orbital period (81.08 minutes). Very lickely, they are early superhumps, as expected from a WZ Sge system. The smaller modulation resembles quasi-periodic oscillations. This is one of the most fashinating lightcurve I have ever seen: enjoy it at the highest resolution, to see the many oscillations! My second run was on Sept. 12. The star was about 2 mag. fainter. I covered the star for about 5 hours, because of clouds early in that evening (but the conditions were excellent during the run). The resulting lightcurve is still very complex and different from the previous one (1 week older!). Again, I worked unfiltered, using the same integration time (10 sec) and setup as above. The plot is below: (Click on the plot to get the full-res graph) Again, larger variations appear with smaller and faster ones. The PDM analysis provided a period estimate of 1.33 +/- 0.09 h, marginally shorter than Porb. Weather conditions improved the next day and on Sept. 13 evening the sky was truly excellent. I started a very long run at 18:00 UT and it lasted more than 10 hours, with constant weather. I used the very same setup and the same integration time (10 sec), again going unfiltered. The star was about 0.1 mag fainter than the previous night. The resulting lightcurve is stunning. (Click on the plot to get the full-res graph) The profile of the lightcurve changed dramatically, suggesting the emergence of superhumps. But small-scale fluctuation are still visible. PDM period analysis on the whole dataset provided a candidate of 1.37+/-0.02 h, marginally longer than Pord: this can perhaps suggest that genuine superhumps are growing. Enjoy it at the highest resolution, to see the many oscillations! On Sept. 14 I started at 17:50 UT, with the same setup and integration time (10 sec). The run ended after 5 hours because clouds entered the sky. The star was a bit fainter than the previous night, showing a completely different curve - once again! (Click on the plot to get the full-res graph) Period analysis using this dataset provided a candidate of 1.40 +/- 0.08 h, significantly laterger than Porb. This may suggests that true superhumps are emerging. Gianluca Masi The Virtual Telescope - 14 September 2007

The extremely rare outburst

of V455 And (formerly HS2331+3905)

V455 And , imaged on Sept.5.9, 2007. The variable is the brightest star nar the center.

On Sept. 4.775 H. Maehara (Japan) reported that the variable star HS 2331+3905 (now V455 And) was in outburst at mag. 14.6, for the first time since the discovery of its cataclysmic nature (2004). Hints were for a candidate of the rare and fashinating WZ Sge group. Over the following hours, it rises again and again.

Once heard of that alert, I planned an observing session with the Virtual Telescope, using the main scope (C14-f/8 on Paramount ME + SBIG ST8-XME, NABG). On ept. 5, during the evening twilight, I slewed the telescope to the star, finding it VERY bright (brighter than mag 9.0). I started time-resolved photometry and real-time data reduction. Soon, I realized that the star was near its maximum and humping. I was able to cover the star for about 9 hours, under excellent sky conditions. I observed unfiltered, to keep th eintegration time as short as possible (10 seconds). The resulting lightcurve was amazing.

(Click on the plot to get the full-res graph)

The star showed a very complex modulation: larger ones (0.4 mags in full amplitude), with smaller and faster ones. PDM period analysis provided a period candidate of 1.35 +/- 0.05 h 81 minutes), consistent with the orbital period (81.08 minutes). Very lickely, they are early superhumps, as expected from a WZ Sge system. The smaller modulation resembles quasi-periodic oscillations. This is one of the most fashinating lightcurve I have ever seen: enjoy it at the highest resolution, to see the many oscillations!

My second run was on Sept. 12. The star was about 2 mag. fainter. I covered the star for about 5 hours, because of clouds early in that evening (but the conditions were excellent during the run). The resulting lightcurve is still very complex and different from the previous one (1 week older!). Again, I worked unfiltered, using the same integration time (10 sec) and setup as above. The plot is below:

(Click on the plot to get the full-res graph)

Again, larger variations appear with smaller and faster ones. The PDM analysis provided a period estimate of 1.33 +/- 0.09 h, marginally shorter than Porb.

Weather conditions improved the next day and on Sept. 13 evening the sky was truly excellent. I started a very long run at 18:00 UT and it lasted more than 10 hours, with constant weather. I used the very same setup and the same integration time (10 sec), again going unfiltered. The star was about 0.1 mag fainter than the previous night. The resulting lightcurve is stunning.

(Click on the plot to get the full-res graph)

The profile of the lightcurve changed dramatically, suggesting the emergence of superhumps. But small-scale fluctuation are still visible. PDM period analysis on the whole dataset provided a candidate of 1.37+/-0.02 h, marginally longer than Pord: this can perhaps suggest that genuine superhumps are growing. Enjoy it at the highest resolution, to see the many oscillations!

On Sept. 14 I started at 17:50 UT, with the same setup and integration time (10 sec). The run ended after 5 hours because clouds entered the sky. The star was a bit fainter than the previous night, showing a completely different curve - once again!

(Click on the plot to get the full-res graph)

Period analysis using this dataset provided a candidate of 1.40 +/- 0.08 h, significantly laterger than Porb. This may suggests that true superhumps are emerging.

Gianluca Masi

The Virtual Telescope - 14 September 2007