[vsnet-chat 4367] Re: re V1436 Aql

[Thom Gandet <tgandet@mindspring.com>]

John, et al

crawl@zoom.co.uk wrote:
>   As I say though, I can't think of any red dwarf eclipsing binaries,
> at least no large amplitude ones.

   RW Tri comes to mind - apparently an Algol eclipser with a white
dwarf companion and CV-type behaviour as well.  The spectral type
of the cool component has been quoted as M0V.  The range is about
3 mags in V with a period of ~0.23 days; max. is about 12.50.  U
Gem's cool component is also a middle-ish M dwarf.

> 
> I doubt that this nearby red dwarf is an eclipsing binary.

   Most likely a flare star; but that shouldn't stop the search
for eclipses, of course.


Best,
Thom

P.S.  The CCD camera came back yesterday from being repaired, so
I'm way behind on e-mail.  (Not that I wasn't before yesterday!)

  



> 
> Let's look at the Hipparcos data.
> 
> At V around 9.5 this object is below the nominal cut off point of that
> catalogue, and is probably only included because of it being a nearby star.
>  Many data entries for this star in the Hipparcos catalogue are blank,
> which means the data couldn't be safely deduced, which is usually
> consequent upon the faintness and/or extreme colour of a star.
> 
> This happens to be a cpm binary with a comes at around 4.2 arcsec [1985].
> This means that both stars will have been in the 10 arcsec field of the
> Hipparcos instrumentation within in which objects cannot be seen
> separately.  Given the already noted fact that this object is below the
> nominal limiting magnitude of the Hipparcos experiment, and that despite
> this the same experiment is capable of picking up photons from the 12th mag
> comes, which being so faint would not have had a separate solution, and
> also that the bright star itself is quite red at B-V about 1.8, again a bit
> of a problem area for faint end Hipparcos objects, you have to start
> worrying about the assumption of eclipses.  Chris Lloyd has already noted
> difficulties with the epoch photometry.
> 
> ANYWAY, let's look at the Tycho data, from the independent star mapping
> instrumentation of the Tycho experiment.
> 
> The Tycho experiment had a limiting magnitude below the V about 9.5 for
> this object so there are is no problem in that regard, and indeed the
> Tycho1 catalogue lists it as having a scatter in VT of only 0.28 mags,
> which could more or less be noise as far as the Tycho experiment is
> concerned, and nothing compared to the 2 mags range listed in the Hipparcos
> Catalogue.  Tycho2 actually gives the standard error on the VT magnitudes
> as being _0.029_, which is even less!  Interestingly, BT is about 11.4, or
> near what Hipparcos quotes as being the minimum in Hp... ...a typo crept in
> somewhere?
> 
> Unfortunately the Tycho1 epoch photometry for this star is in annex B,
> which is only accessible via the CDS, so I'll have to order that.  When I
> get it I'll forward it to vs-chat.  Tycho epoch photometry is two colour,
> BT and VT, and most EA type eclipsing binaries show colour changes during
> eclipse, so that might be interesting.  As I say though, I can't think of
> any red dwarf eclipsing binaries, at least no large amplitude ones.  I'm
> willing to stand corrected.
> 
> Doesn't stop the star being variable though, although flaring is the only
> activity I'm aware of for red dwarfs.
> 
> IMPORTANT : when folk use Hipparcos data they should really ensure that
> they take into account _all_ the data for that object in the main
> catalogue, including all the flags, which have significant bearing on the
> quality and nature of the data, and stop taking isolated chunks of data and
> treating it as sacrosanct.  It is often also a thought to check what the
> Tycho data for the object says as well, not only because that experiment
> used independent instrumentation and data processing, but also because it
> gives two colour photometry, frequently with two colour epoch photmetry for
> interesting objects, and thus enables a deeper assessment of the objects
> nature.
> 
> Cheers
> 
> John
> 
> John Greaves, UK

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