The hot RCB star V348 Sgr is now rising from extreme (perhaps record faintness) minimum. Looking at the observations in the AAVSO Database, the star seems to have been near max in March-April of 2013 followed by a divebomber-like plummet of near 6 magnitudes in 40 days or less. Possibly the record faint B and V measures of July 11 2013 near mag 19 need to be reversed, the star typically being brighter in V than in B. There seems to have been a weak, partial recovery from V=18.8 to V=16.6 in Sept of last year then no other sightings for the remainder of 2013 and into 2014 until the star is seen back at extreme minimum in March of this year. It appears to have remained near minimum through May 2014 until the most recent observations of June and July reveal the rise, in Rc band, from 16.5 to near 15.0 within the last two weeks (roughly from 17.5 to 16.0 in the V band I would think). Visual and V observations may reveal this *super* variable in the 15's during the next week or so if the current comeback persists.
Good Observing to All,
I did an exposure using a V filter and posted the result (15.63). However there are very few comp star is the field and there seems to be no R and B comp starts in the magnitude range I am seeing. What comp start should I be using?
In V I like using the 130 (BCC-932) at V=12.958 and the 144 (BCC-939) at V=14.396.
As you see from the AAVSO photometry page for this variable, there are no Rc band comparisons listed yet. However, at least two of the listed V comps aren't too bright, are reasonably isolated, and have known B-V indexes, which often allows *approximate* Rc values to be temporarily employed until something better becomes available. The comparisons I employ using this method are the 127 (BCC-955) at Rc=12.06(approximate) and the 130 (BCC-932) at Rc=12.76(approximate).
From your recent V observation we can see V348 Sgr has come up about 1 magnitude in the past week. Should this rate of brightening continue we can expect visual observers to begin to pick it up soon as well.
Thanks for your keen interest and continued good observing !
would there be someone interested in a near nightly snapshot coverage of this star? I have a remote observatory and could add the stars to my observing list. Near nightly coverage is possible for most of the season.
This was an interesting journey down "memory lane." I had calibrated the V348 Sgr field as part of a large project of CV calibration with Bruce Sumner. At the time, the classification was "unique." I calibrated it during 1998; I've attached one of the NOFS images with the variable circled (at the time, it was about V=18.1 and B-V = 0.47; the chart is north up, east left, and about 4.5x4.5arcmin). I only observed the field at B&V, except for one night where I tried to go fainter at R to see the nebulosity. Note that this is a very crowded field; when the variable is faint, you will suffer contamination from the many nearby stars, and other observers will mistake the 15th magnitude about 15arcsec east as being the variable. Note that this timeframe (August 1998) had no observations in the AAVSO database, even fainter-thans. It turns out that Arlo Landolt also follows this star, and has lots of data that have never been submitted.
Josch, if you can do two-filter work, say B and V, your nightly monitoring would be great and would be an interesting comparison to R CrB or other stars of this class.
I have taken V348 Sgr B, V and I images on two nights (so far each night V, I or B, V images). However I would need also B and I magnitudes of the comp stars I use, namely the ones mentioned before: 000-BCC-932 and 000-BCC-939. If other comps have B, V I vand magnitides I could also change the comps.
in the meantime we are a few years ahead and I did monitor the star in even three filters (BVI). Have you had a look. There was quite some drastic variation visible in the past years.
Any feedback would be appreciated. I could continue the monitoring also during the present season.
V348Sgr has rissen to to close to mag 12.5 in V coming from mag 17.5 or so. I am keeping an eye on it as weather permits.
I continued nightly snapshots also during the present season. The object is very dim in all filters.