RW Cephei great dimming

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  • #614498
    Jeremy Shears
    Participant

    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:
    #614519
    Paul G. Abel
    Participant

    This looks fascinating Jeremy! I will take a look!

    #614529
    Robin Leadbeater
    Participant

    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 ?

    #614535
    Robin Leadbeater
    Participant

    Here 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 dust

    VSX 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=13110

    Cheers
    Robin
    EDIT- trying to get the link working.. and failing 🙁 cut and paste it if you need to

    #614537
    Robin Leadbeater
    Participant

    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)

    Cheers
    Robin

    #614558
    Duncan Hale-Sutton
    Participant

    My visual observation tonight at 18.50 UT put it at about magnitude 7.6.

    Duncan.

    #614780
    Robin Leadbeater
    Participant

    A 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

    #614786
    Jeremy Shears
    Participant

    Robin,
    contact Prof Constantino Sigismondi at ICRA. His email is in the ATel I linked at the top
    Jeremy

    #614874
    Duncan Hale-Sutton
    Participant

    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?

    Duncan

    #614881
    Robin Leadbeater
    Participant

    It 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=12378723

    Cheers
    Robin

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