Re: [AAVSO-DIS] RU Vulpeculae and its star field

[Thomas Droege <tdroege2@earthlink.net>]

Tass has RU Vul at 309.719+23.258  Entering RU Vul into Vizier gets a GCVS
position of 309.7196+23.2585
or 20:38:52.9 +23:15:31  This is presently star 1941815 in the tass data
base.  The ID numbers are subject to change, the position is not.  

The tass data base found 33 measurement pairs, and the star looks variable
with 100+ day period and a 0.6 mag variation in V.  Somewhat less in I. . 
Not enough data to pin down the period.  There is scatter in the data
points but it is consistent with the published errors.  Brian says "
...bearing in mind that the second is not always well-calibrated."  I would
prefer to say that the scatter has been calibrated but is larger than those
living on mountain tops are used to seeing.   Looking at the AAVSO plot for
RU Vul, I would estimate that the tass data has a factor of 4 less scatter.


My best estimate of the 97 star is a star at:  

309.553+23.344  This is star 1941738 in the present tass data base.  There
are 24 measurement pairs.  The scatter in V is 9.7 to 9.86.  With a sigma
claim of 0.5 for a star of this brightness, this is consistent with a fixed
star.  OK, it is on the upper end of the probable error.  More data is
needed.  

My best estimate of the 105 star is at:

309.564+23.332  This is star 1941750.  There are 24 measurement pairs.  The
scatter in V is 10.49 to 10.68.  This is again consistent with a fixed
star.  

I did several plots of the tass data to try to compare it with the AAVSO
chart.  There are just too many stars in the tass plot to make sense of it.
This even after I removed all the stars with less than 20 measurements.  We
need a program that plots stars as circles proportional to the magnitude
(and with error bars).  Possibly someone will work on this.  Probably
someone has already done it, but I could not find it.  Michael built such a
program into his data base for the Mark III data.  Michael, is it easy to
export this program? 

Tom Droege


> [Original Message]
> From: Brian Skiff <Brian.Skiff@lowell.edu>
> To: <gianluca_1@fastwebnet.it>
> Cc: <aavso-discussion@mira.aavso.org>
> Date: 9/5/2004 4:01:00 PM
> Subject: Re: [AAVSO-DIS] RU Vulpeculae and its star field
>
>      Given that the chart data are from no more recent than 1942, it is
> not surprising to find that a particular comp star has inconsistent
> values.  You can check this yourself.  First determine coordinates
> using your Skymap program or some other method.  Then look up the star(s)
> in the ASAS-3 and/or TASS MkIV query pages:
>
> http://www.astrouw.edu.pl/~gp/asas/asas3_catalog.html
>
> http://sallman.tass-survey.org/servlet/markiv/template/DataDownload.vm
>
> ...bearing in mind that the second is not always well-calibrated.
> I would also look at the stars in Tycho-2 using the Strasbourg VizieR
> catalogue-query utility:
>
> http://vizier.u-strasbg.fr/cgi-bin/VizieR
>
> ...where Tycho-2 is item I/259 in this system.  If the Tycho-2 scatter
> on the photometry is small and/or the scatter in the ASAS data is small,
> then the star is most likely constant.  The ASAS data also should give
> a very good mean V magnitude that will be reliable to ~0.03 mag or so.
> Likewise Tycho-2, though a small correction is necessary to adjust the
> catalogue values to standard V.
>      It is helpful when posing queries such as this to provide coordinates
> for the stars rather than noting only "97var? on the chart for RU Vul".
> You really can't dig into available data without _coordinates_ or a
> principal name, such as HD or BD number.
>
> \Brian
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