9 December 2022 at 9:58 pm #614498Jeremy ShearsParticipant
An ATel from Wolfgang Vollmann and Costantino Sigismondi today (https://www.astronomerstelegram.org/?read=15800) suggests that the red hypergiant RW Cep might undergoing a dimming event similar to that observed in Betelgeuse a few years ago. It normally shows irregular variations between magnitudes 6.0 and 7.3. However, it has recently been fading as is currently mag 7.7 (see VSS light curve).
Worth following to see how faint it gets.
Attachments:11 December 2022 at 10:51 am #614519Paul G. AbelParticipant
This looks fascinating Jeremy! I will take a look!11 December 2022 at 2:11 pm #614529
Some (PEP) photometry in the IR might be interesting. Betelgeuse hardly faded at all in H and J. There is no history for RW Cep in those bands in the AAVSO database though. Does anyone in the BAA have this capability ?11 December 2022 at 9:28 pm #614535
Here is a spectrum tonight (R=1000 using an ALPY 600 with a narrower than usual 10um slit)
It is very red but clearly heavily reddened by interstellar or circumstellar dust
VSX suggests a very wide range of spectrum classifications ranging from G to M2 but Keenan suggests K2i in his 1989 catalogue.
Using the B,V brightness values in SIMBAD, this would imply for a K2i star an E(B-V) = 0.99. Dereddening my spectrum by this amount indeed gives a good match to the Pickles standard for K2i both in terms of the continuum shape and more importantly in the spectral line details (My spectrum is a slightly higher resolution which would explain the higher apparent intensity of the lines in my spectrum)
EDIT- trying to get the link working.. and failing 🙁 cut and paste it if you need to11 December 2022 at 9:35 pm #614537
I suspect the M2 classification may have come from the colour index which would match an M star without reddening but the lack of molecular bands in the spectrum immediately shows we are dealing with a hotter star here (significantly hotter than Betelgeuse)
Robin12 December 2022 at 8:28 pm #614558Duncan Hale-SuttonParticipant
My visual observation tonight at 18.50 UT put it at about magnitude 7.6.
Duncan.20 December 2022 at 12:56 am #614780
A high resolution spectrum (R=15000) taken tonight shows H alpha to be in emission
There are a number of publicly available archived high resolution spectra taken with the ELODIE spectrograph at Observatoire Haute Provence between 1998 and 2005. None of these show H alpha in emission so this may be unique to this dimming.
Plots of the ELODIE spectra and comparisons with my spectra at both low and high resolution can be seen here on my website
Is there any professional interest in these observations ? If so who should I be talking to for guidance on what specifically I should be focussing on (resolution, specific regions/lines)
20 December 2022 at 10:08 am #614786Jeremy ShearsParticipant
- This reply was modified 1 month, 1 week ago by Robin Leadbeater.
contact Prof Constantino Sigismondi at ICRA. His email is in the ATel I linked at the top
Jeremy24 December 2022 at 11:04 pm #614874Duncan Hale-SuttonParticipant
Another look at this star this evening. I was comparing it to stars E (=7.3) and H (=7.8) on chart 312.02. I definitely think its brightness is between these two stars and a bit closer to E than to H. My estimate was E(1)V(2)H that is magnitude 7.5 (7×50 bins, 18:55 UT). Interestingly the AAVSO plot for this star is showing some quite varied estimates recently even between CCD observations so I am not quite sure what is going on here. What are other people seeing?
26 December 2022 at 11:13 am #614881
- This reply was modified 1 month, 1 week ago by Duncan Hale-Sutton.
It seems from this survey RW Cep is dimming by ~ the same amount in Ic and V
which is significantly different to the Betelgeuse event.
(Thanks to “VY Canis Majoris” on Cloudy Nights for the heads up on this)
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