› Forums › Variable Stars › RW Cephei great dimming
- This topic has 12 replies, 4 voices, and was last updated 11 months, 1 week ago by
Robin Leadbeater.
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9 December 2022 at 9:58 pm #614498
Jeremy Shears
ParticipantAn 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. Abel
ParticipantThis looks fascinating Jeremy! I will take a look!
11 December 2022 at 2:11 pm #614529Robin Leadbeater
ParticipantSome (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 #614535Robin Leadbeater
ParticipantHere is a spectrum tonight (R=1000 using an ALPY 600 with a narrower than usual 10um slit)
https://britastro.org/specdb/data_graph.php?obs_id=13110
It is very red but clearly heavily reddened by interstellar or circumstellar dustVSX suggests a very wide range of spectrum classifications ranging from G to M2 but Keenan suggests K2i in his 1989 catalogue.
https://articles.adsabs.harvard.edu/pdf/1989ApJS…71..245K
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)
https://britastro.org/specdb/view_image.php?obs_id=13110Cheers
Robin
EDIT- trying to get the link working.. and failing 🙁 cut and paste it if you need to-
This reply was modified 1 year, 8 months ago by
Robin Leadbeater.
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This reply was modified 1 year, 8 months ago by
Robin Leadbeater.
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This reply was modified 1 year, 8 months ago by
Robin Leadbeater.
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This reply was modified 1 year, 8 months ago by
Robin Leadbeater.
11 December 2022 at 9:35 pm #614537Robin Leadbeater
ParticipantI 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)
Cheers
Robin12 December 2022 at 8:28 pm #614558Duncan Hale-Sutton
ParticipantMy visual observation tonight at 18.50 UT put it at about magnitude 7.6.
Duncan.
20 December 2022 at 12:56 am #614780Robin Leadbeater
ParticipantA high resolution spectrum (R=15000) taken tonight shows H alpha to be in emission
https://britastro.org/specdb/data_graph.php?obs_id=13128
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
http://www.threehillsobservatory.co.uk/astro/RW_Cep/rwcep_elodie_archive_THO_2022-12-19_lowres.png
http://www.threehillsobservatory.co.uk/astro/RW_Cep/rwcep_elodie_archive_THO_2022-12-19_Halpha.png
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)
Cheers
Robin-
This reply was modified 1 year, 8 months ago by
Robin Leadbeater.
20 December 2022 at 10:08 am #614786Jeremy Shears
ParticipantRobin,
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-Sutton
ParticipantAnother 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?
Duncan
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This reply was modified 1 year, 7 months ago by
Duncan Hale-Sutton.
26 December 2022 at 11:13 am #614881Robin Leadbeater
ParticipantIt seems from this survey RW Cep is dimming by ~ the same amount in Ic and V
http://kws.cetus-net.org/~maehara/VSdata.py
which is significantly different to the Betelgeuse event.
(Thanks to “VY Canis Majoris” on Cloudy Nights for the heads up on this)
https://www.cloudynights.com/topic/854288-rw-cephei-great-dimming/?p=12378723Cheers
Robin12 September 2023 at 5:09 pm #619102Duncan Hale-Sutton
ParticipantThis star has now returned to its normal range of magnitudes. There is a paper that has appeared in the Astronomical Journal (https://iopscience.iop.org/article/10.3847/1538-3881/ace59d) where the authors have imaged the star during the great dimming using interferometry. They say that they saw an asymmetry in the stars photosphere which suggests a mass ejection of material. This would have cooled and formed a dust cloud that dimmed the star. This is similar to what happened to Betelgeuse in 2020.
12 September 2023 at 9:24 pm #619124Robin Leadbeater
ParticipantThe H alpha emission I mentioned in the VSSC article on RW Cep (and referenced in the paper) has also reduced in the past 3 months as the brightness increased so it looks like it is associated with the dimming.
Cheers
RobinAttachments:
12 September 2023 at 9:40 pm #619126Robin Leadbeater
ParticipantThe dimmed spectrum divided by the current spectrum (green)
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