Whatever happened to Megrez?

Home Forums General Discussion Whatever happened to Megrez?

Viewing 20 posts - 1 through 20 (of 34 total)
  • Author
    Posts
  • #574558
    Alan Thomas
    Participant

    I went into the garden tonight at 21.55 to scan the sky.

    I was startled to find that Megrez in Ursa Major (Delta Ursae Majoris), high in the sky,  had disappeared!  Was there something wrong with me? Or was there a temporary obscuration? Or what? Help!

    #582149
    Peter Anderson
    Participant

    This post piqued my interest so I did a little research:

    My Research From ‘Wikipedia’ : This star has an excess emission of infrared radiation, indicating the presence of circumstellar matter. This forms a debris disk around an orbital radius of 16 Astronomical Units from the star. This radius is unusually small for the estimated age of the disk, which may be explained by drag from the Poynting–Robertson effect causing the dust to spiral inward.

    From another internet site:

    William Creed

    Thursday, 2nd March 2017 5:58:14 AM

    When I was a kid in around 1955 to 1969 that star was very visible in the night. Why has it seemed to fade over the 20 some years.

    And another site:


    Is it just me or is the star that connects the dipper with the handle fading out
    There are no clouds its a cold , clear night
    For those that can , step outside and observe
    I have never come across this before 

    Its barely there if at all(Feb 2013)

    Finally Patrick Moore, in his book ‘Stargazing’ in 2001, at page 25 states:

    “Old astronomers of more than 1,000 years ago stated that it was as bright as the other Ursa Major stars. Either they were wrong or (less probably) Megrez has actually faded about a magnitude since then.”

    My question – Is it another case of dust obscuration – now becoming more rapid ????  Trouble is, at 57 degrees north it is just about inaccessible from here in Brisbane Australia…

    #582151
    Peter Anderson
    Participant

    Seems I was getting excited over nothing. A colleague of mine emailed me some AAVSO information including the attached graph. Maybe in poorer sky conditions with the star near the limit of visibility,it appears to be fainter…  I just don’t know.

    #582152
    Peter Anderson
    Participant

    The diagram above starts at 31st December 1954 and ends at 25th March 2020. (Bit difficult to read). It shows little apparent variation in magnitude.

    #582153
    Nick White
    Participant

    I looked at it two or three nights ago while searching for the comet and thought to myself “That’s dimmer than I remember” and then carried on without a second thought. There doesn’t appear to be any AAVSO data for two or three nights ago.

    #582154
    Alan Thomas
    Participant

    Thanks for those comments. So far I am reassured that I am not going nuts!

    Alan

    #582155
    Robin Leadbeater
    Participant

    I was taking spectra last night and the signal from the target suddenly disappeared. I went outside to check and as far as I could tell the sky was completely clear. I went back inside and watched as the signal came back up.  Half an hour later the same thing happened but this time I looked outside to find it was foggy, putting an end to observations

    #582156
    Alan Thomas
    Participant

    I had been out observing for a couple of hours earlier in the evening and was just having a final look around. So far as I can tell, the skies were perfectly clear. But I suppose a passing puff of cloud might be responsible. Or some other obstruction of course.

    What surprised me was that Megrez was not simply faint but invisible, at least to the naked eye. That’s something I have never seen (or not seen) before in over 60 years of skywatching.

    I will be having a closer look tonight with optical aid.

    #582157
    Alan Thomas
    Participant

    I went out at 20.30 and again at 21.50. I could detect Megrez with the naked eye, but only just, a little more easily with averted vision. It certainly seems unusually faint – but is it?

    #582159
    Gary Poyner
    Participant

    This is from KWS (Kamogata/Kiso/Kyoto Wide-field Survey).  delta UMa also has a NSV designation (NSV 5513)

    Gary

    #582160
    Alan Thomas
    Participant

    Hi Gary

    I am not a variable star observer. How would you interpret these data?

    Thanks

    Alan

    #582161
    Gary Poyner
    Participant

    Hi Alan,

    Well this is the first time I’ve seen a plot of delta UMa myself.  VSX says the variability is of unspecified type, but this link suggests a possible EB    http://liber.onu.edu.ua/pdf/astro/all/OAP_9/000_pdf/bryukh.pdf

    It’s quite interesting that the amplitude of the fades vary from one fade to the next.  Be nice to see a much longer plot.   My eyes are possibly seeing a secondary wave on that light curve.

    Gary

    #582162
    Robin Leadbeater
    Participant

    Interesting that the variability in I is much less than in V. Reminiscent of the recent Betelgeuse fading

    #582163
    Robin Leadbeater
    Participant

    Is the short term variation  in KWS V mag real ?  eg

    #582164
    Alan Thomas
    Participant

    I don’t know what the Ic V and B designations for the plots refer to, but do I detect a downward trend in the red plot – and an upward in the green? (this refers to Gary’s earlier post)

    #582166

    According to SIMBAD it is of A2Vn C spectral type. I also found reference to a debris disk in Wikipedia linking to a paper by Wyatt et al 2007 https://arxiv.org/pdf/astro-ph/0703608.pdf.

    So it is a main sequence A-type star and the paper quotes an age of 300 Myr, though I think that comes from another paper (I’ve not read the paper in detail, just skimmed a few bits). I am surprised a main sequence star could have a debris disk as I thought this was associated with young stars. If I’ve understood the paper there are collisions in the debris disk generating dust and an IR excess. Perhaps the variation in luminosity is due to variable obscuration by the dust?

    Interesting how such a well known and prominent star can throw up surprises to us, well spotted Alan!

    #582167
    Robin Leadbeater
    Participant

    B,V Ic correspond to the band in which the brightness was measured. (The survey instrument uses a CCD camera and wide field lens).  V corresponds roughly to what the eye sees Ic is the near infrared. There are small long term average trends from season to season but the  variation from day to day/week to week of up to 0.5 magnitudes seen in the V data would be  obvious by eye if real. The very tight error bars on the points would suggest they are real but I am somewhat sceptical.

    #582168
    Alan Thomas
    Participant

    Many thanks, Robin, for the clarification on the data series. I never thought variable stars were that interesting – but I’m beginning to wonder now!

    #582169
    Jeremy Shears
    Participant

    I too am sceptical about those V-band variations in the KWS, Robin. In spite of the tight errors bars.

    The interesting thing is there whilst there are many photometric surveys of faints stars, there are very few surveys of bright stars like Megrez.

    I think we should all take a leaf out of Alan’s book (me included!) and look up at the sky with our naked eyes to check if there is something out of the ordinary. After all, it was only a few weeks ago that Betelgeuse was observed to be dimming.

    #582170
    Alan Thomas
    Participant

    Thanks Andy!

Viewing 20 posts - 1 through 20 (of 34 total)
  • You must be logged in to reply to this topic.