Re: re star 1622 in october data

[Michael Sallman <msallman@pro-ns.net>]

Per John's suggestion (thanks, John, for the response), anyone care to 
offer up some insight?

As John mentions below, the Tycho Main Catalogue shows a parallax of 
124.1 mas (with an error of 89.9 mas). I note that the astrometry flag 
is "X" which means "a dubious astrometric reference star", and also that 
the proper motion values (-76.60 & 92.20) are more than 10 times those 
in the other catalogs (for example, Tycho-2 has values of -3.1 & -7.1).
Also, this star doesn't appear to be in the Yale Parallax Catalog, however.
So, what's the verdict? Is the Tycho parallax data accurate for this star?

Thanks,
Mike


Mr a b wrote:

> Hiya
>
> re star 1622.
>
> You'd better ask on the list if someone can comment on how accurate
> tycho2 parallaxes are for stars like this, as the tycho2 parallax for
> it, and the subsequently derived absolute magnitude, not only suggests
> that it is a nearby star, but possibly even a white dwarf, yet I know
> of no white dwarfs that exhibit this amplitude of pulsational variation.
>
>
> An abs. mag. of 12 couldn't be an RR Lyr star though, so as I say, the
> parallax question needs answering.  The almost total lack of proper
> motion measured by tycho doesn't tally with this being a nearby star,
> although it is not impossible for it to be only moving in the line of
> sight.
>
> Cheers
>
> John
>
>