Affiliation
American Association of Variable Star Observers (AAVSO)
Fri, 12/16/2022 - 23:42
AAVSO Alert Notice 804 reports on the dimming of the semiregular variable RW Cep. Please see the notice for details and observing instructions.
There are threads for this campaign under the following AAVSO forums:
- Campaigns and Observation Reports: https://www.aavso.org/rw-cep-dimming
- Long Period Variables: https://www.aavso.org/rw-cep-dimming-01
Please subscribe to these threads if you are observing this star so you can be updated. Join in the discussion or ask questions there!
Many thanks, and Good observing,
Elizabeth O. Waagen, AAVSO HQ
I have three recent high SNR spectra (R~1000) of RW Cep in the BAA spectroscopy database where they can be downloaded.
https://britastro.org/specdb/
They have been carefully (relative) flux calibrated using two different reference stars measured before and after so should represent a good reference of the current spectrum (The estimated precision in the continuum is +-5% 4200-7500)
The spectra can be seen here on my website
http://www.threehillsobservatory.co.uk/astro/RW_Cep/RW_Cep_dimming.html
The estimated spectral classification based on these spectra is currently K4i with 0.65 extinction E(B-V), shown there overplotted on the Pickles K4i reference spectrum (total galactic IS extinction in this direction is 0.75 E(B-V) )
There are two earlier spectra in the AAVSO database from 2020 and 2021 which show significantly different continuum shapes, implying a much higher temperature. The features in these spectra are consistent with my spectra however, particularly the broad absorption at ~6250A, attributed to TiO and normally absent in stars hotter than K2
There is also a single high resolution spectrum in the ELODIE archive which looks approximately similar to my current spectrum in both continuum and spectrum features.
Cheers
Robin
A high resolution spectrum (R=15000) taken tonight shows H alpha to be in emission (available for download from the BAA spectroscopy database)
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 what specifically should I be focussing on (resolution, specific regions/lines)
Thanks
Robin
A paper posted on tonight's (UT 2023 Jul 12) astro-ph describes CHARA array observations of RW Cep, resolving the photosphere for the first time:
https://arxiv.org/abs/2307.04926
The Great Dimming of the hypergiant star RW Cephei: CHARA Array images and spectral analysis
...obviously comparing its recent dimming event with the one of Betelgeuse. AAVSO data mainly from Wolfgang Vollmann are shown as part of the discussion.
\Brian
It also cites my spectroscopy but unfortunately I was not contacted in advance of publication so the appropriate reference was not included. (hopefully it should be included in the final published version) My paper on this including the spectra can be found in the BAA VSS Circular
BAA Variable Star Section Circular, No.95, March 2023, 7-12
https://britastro.org/vss/VSSC195.pdf
and the spectra (fits files) in the BAA spectroscopy database
https://britastro.org/specdb/
Cheers
Robin