The WC8 Wolf-Rayet star WR 53 (HD 117297) seems to be much fainter than usual.
All surveys (ASAS-3, HIPPARCOS, APASS) recorded it around V= 10.53 over the past decades.
A couple of nights ago Rod Stubbings detected it visually at v= 11.4 and requested follow-up observations by Peter Nelson. Peter got a V image showing it around V= 11.66 last night (in Australia, so during daylight in the Americas).
A 1.1 mag. dip in a Wolf-Rayet star suggests an eclipse. An eclipse lasting more than a day suggests a long period. But the longer its duration the more unusual these systems are, so it would be important if observers can go out tonight and check this star as long as possible. Time series would be useful because the eclipse (assuming that is what this is) might be already ending or starting to end and having a continuous light curve would show what type of variability we are witnessing.
WR 53 is in Centaurus, at 13 30 53.25 -62 04 51.9 (J2000.0).
A sequence has been created by the Sequence Team so you can make charts with VSP entering the name WR 53 or HD 117297.
Comment your findings here and submit your data to the AID.
Cheers,
Sebastian
Hi Sebastian,
I will give it a try for some time tonight.
Regards,
Josch
Some recent observations of WR 53.
WR 53 150707.477 105
WR 53 150715.554 107
WR 53 150719.450 110
WR 53 150720.467 114
WR 53 150720.606 115
Regards,
Rod.
This variable is too faint for the normal BSM survey. However, there are two survey targets that are in the vicinity (V0659 Cen and V0967 Cen), so there are a dozen or so observations of WR53 in the internal database. The latest was in May, so they won't cover the recent fading, but might help in understanding the out-of-eclipse behavior. When I finish with APASS DR9 this week, I'll extract the older photometry.
Arne
Some late WC-type WR stars undergo eclipse-like events due to dust formation in their stellar winds. My recollection is that the depth of the dip could be over 1 mag and that the initial fading event could take place in about one week, similar to what's been observed so far with WR 53. Also, the spectral type of WR 53 (WC8/9) is consistent with the dust-formation scenario.
Perhaps someone could observe WR 53 with an SA100/200. I remember reading a paper about an eclipse-like event in another late WC star, WR 104, and the high-ionization emission lines became very weak while low-ionization lines did not. That event was attributed to dust formation.
Colin
That sounds like a possible explanation.
Colin,
WR 104 has a very different light curve and the fadings events by dust are reflected in the star's colors (J-K= 4.2, B-V= 1.8).
But I think you are right.
This paper mentions eclipse-like fadings in some other WC stars.
This is the HIPPARCOS light curve of V1485 Aql.
That fading certainly looks like an eclipse and the star stays almost constant at maximum most of the time like WR 53. Colors are J-K= 2.5 and B-V= 1.3.
WR 53 has J-K= 1.9 and B-V= 0.6 so it is also obscured.
Other stars show the same behaviour.
I think you solved the puzzle. Can someone get multicolor data of the current event? The dip should be deeper in bluer wavelenghts.
Cheers,
Sebastian
Hi,
I can get B and V data. V Data from last nights tiome series have been submitted to AAVSO.
Can snapshot data be useful instead of time series?
Josch
Hi Josch,
Your observations confirmed Rod's detection.
The changes seem to be slow.
About the multicolor photometry I would just get a couple of measures now that it is faint to compare with some measures made when it is back to quiescence to see how the color behaved. I wouldn't make multicolor time series.
Try to observe it tonight if possible.
Thanks!
Sebastian
Hi Sebastian,
I have been observing time series last night in B and V. So from tonight onwards I will switch to snapshots in BV.
Data will be sent to AAVSO.
Regards,
Josch
There's going to be sequence issues with this one. I've been observing it (inc last night) but was not aware there was a new sequence. Or a sequence at all - apart from my one from from Albert Jones. With all the chart = NA in the obs, I suspect I'm not the only one.
But I may be able to re-work my obs. I'll hold off entering any for a while.
alan
WR 53 is just on the edge of the field of view for V0967 Cen, with the BSM systems. I've uploaded the archival photometry for this object. There might be a small V-band offset; I was using BSM South calibration and I see that this particular field has larger error than most. Based on Josch's data, this looks more like an eclipse than a dust event.
Arne
Sebastian,
I have the following recent for WR 53:
V=10.63 (0.04) on July 27.42269 UT
Rc=10.15 (0.03) on July 27.41769 UT
Ic=9.72 (0.07) on July 27.42144 UT
I'll get these into the DB, likely tomorrow eve.
Steve