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I have just issued this BAA Alert via email.
John Toone (BAA VSS, Shropshire) has reported RY Sgr fainter than normal, at visual magnitude 8.0 on Aug 29 (compared to 6.2 on Jul 8) and has suggested that it might be at the start of a fading episode. Several other observers have also reported the star as being fainter of late. Further observations are urgently requested to determine whether this is the beginning of a deep fade or just a deep pulsation minimum.
RY Sgr is a yellow supergiant of the R Coronae Borealis class. As is typical for the class, its light curve is characterised by a sudden drop in brightness from 6th mag to mag 12 to 14 over a few weeks before gradually brightening over the following several months. The interval between these fading episodes is irregular. The fading is due to the presence of dust clouds of carbon obscuring the star.
RY Sgr is also a pulsating variable, with a semiregular period of 38 days, mag ca 6.5 – 7.5. Observations over the next few days will confirm if the current fainter state is due to one of these pulsations being faint, or the start of a genuine fade. Contributions by observers will help to resolve this question.
The southerly declination of RY Sgr is a challenge for UK-based observers (RA 19h 16m 33s, DEC −33° 31′ 20″), but not impossible for those in the southern part of the country with a good southerly horizon. Observations could be made with binoculars or a small telescope. Observers from countries further south are naturally encouraged to observe the star too.
Finer charts are available at the AAVSO VSP: https://app.aavso.org/vsp/chart/?star=RY+Sgr&scale=A&orientation=visual&type=chart&fov=900.0&maglimit=9.0&resolution=150&north=down&east=right
These can be scaled as desired.Jeremy Shears
Director, VSSCoincidentally I am in the last week of my holiday in Cornwall. And also coincidentally I have brought my telescope! The skies here on the Helford estuary are very dark, especially to the South, but there is a lot of high cloud tonight in the South.
Dave
I could just about find it, and make a measurement – however it was quite challenging as there was a lot of moisture in the air and it was very low on the horizon. I couldn’t see it in my 8×56 binoculars, but found it in my 8″ Dob and 30mm eyepiece (40x). I will upload a record.
Dave
Back up to 7.526V (0.007) on August 30.875
Last night’s oservations were hindered by cloud and not yet analysed.
Definitely brighter, and unlikely to be an RCB dust event on this occasion…
Sep 03.202UT 7.644TG +/- 0.001 SLOOH Chile.
Gary
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