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[vsnet-campaign-nova 29] RE: V382 Vel recent data
Dear Mati and VSNET folks:
The nova is slowly fading.
I think problematic comparison stars are in use. The star is obviously
whiter than before so it's not useful to use red stars for comparison. The
two stars Mati mentions are brighter than the variable, but the red colour
of GSC 8210-00801 makes it look fainter if seen with peripheral or
parafoveal vision ( as most cases with faint stars.)
Furthermore, Tycho
comparisons proved to have a greater error than Tycho 2, evident through the
eyepiece. AAVSO charts use Tycho magnitudes and the sequence ends in 10.8.
It is probably making observers using this chart to put a lower limit for
V382 Vel when the star is really fainter than that.
GSC 8210-01423 (10.00V, 0.45
Tycho2) is too bright and GSC 8210-00801 (10.54V, 1.49 Tycho2) is too red so
they should be avoided for comparison at this stage.
It's better to look for
whiter and fainter stars now and avoid Tycho stars that faint.
An appropriate Tycho 2 sequence would be:
GSC 8614-00500 10.64, 0.44 ( 107 AAVSO/Tycho)
GSC 8210-01225 10.82, 0.42
GSC 8210-00897 11.00, 0.25
GSC 8614-00300 11.05, 0.02
GSC 8210-00423 11.41, 0.73
105 (GSC 8210-00023) and 108 (GSC 8614-00338) Tycho/AAVSO stars are orange
and brighter than the variable so they also should be avoided.
GSC 8210-00897 , the most suitable star at the moment is 0.23 magnitudes
brighter in Tycho than in Tycho 2. I suggest again avoidig the use of Tycho
magnitudes.
Mati's guess was OK: these were the two stars being used (at least by me)
I agree that we should try to get an agreement about which sequence to use.
Best regards'
Sebasti睹 Otero.
----- Original Message -----
From: Mati Morel <morel@ozemail.com.au>
To: <vsnet-campaign-nova@kusastro.kyoto-u.ac.jp>
Sent: Tuesday, July 04, 2000 3:38 AM
Subject: [vsnet-campaign-nova 23] Re: V382 Vel recent data
> The recent observations on V382 Vel (below) suggests that different
> comparison stars are almost certainly in use, and while they may be the
best
> available (Tycho), the discrepancy may cause variations which are not
> intrinsic to the nova.
>
> The two Australian observers from the VSS, RASNZ (Andrew Pearce and Peter
> Williams) are presumably using comparison stars GSC 8210.01423 (9.94V,
0.51
> B-V) and GSC 8210.00801 (10.43, +1.27) as shown on my chart VSM84 of 2000
> March 2000. These two observers have consistently reported the nova at
10.3
> or 10.4. However, the other observers, especially Berto Monard (South
> Africa) and S. Opero (South America) have consistently reported the nova
at
> 10.8. This suggests to me that they are using GSC 8210.01225 (10.77V)
and/or
> GSC 8210.00897 (10.77V) as comparisons. Would this be so, Berto? Being
well
> aware of the vagaries of Tycho mags at this level, errors of a couple of
> tenths in the Tycho mags
> can exaggerate the normal observational errors and produce fictitious
> fluctuations. I am unable to say which of the Tycho mags are the culprit.
> If one is looking for periodic modulations one should ensure the dataset
is
> produced by observers working to the same set of consistent, reproducible
> condtions. The choice of comparison stars can be critical. I doubt that
> these conditions are currently being met.
>
> Cheers,
> Mati
> Morel Astrographics
> c/o M. Morel, 6 Blakewell Rd, Thornton NSW 2322 AUSTRALIA
> *Specialized Charts** Variable Star Studies** Stellar Data**
> 151o38'33" E, 32o46'47"S. morel@ozemail.com.au
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