[vsnet-chat 5556] Re: The curious case of BD+59 224

["Stan Walker" <astroman@xtra.co.nz>]

Hi Brian & Doug,

 

I hadn't taken note of this discussion earlier as the star is 4 degrees below my horizon. But I was a little intrigued by the values posted by Doug and they reminded me of a question I put in another area. Before this, however, the spread of values given by Doug is about 25%. Surely this can't be right? Or do these occur as a result of the difficulty of getting reliable UBVRI measures from Tycho values?

 

I presume that the formulae for translating Bt and Vt to the UBVRI system are those referred to recently by Aaron Price. The question that I asked related to the reliability of these with anything other than unreddened main sequence stars. In doing some BVR photometry which included some Tycho stars I noticed the actual values differed by 10-20% from the values derived using the formulae. That's not much use. I'm reminded of the SPv and SPg systems the Cape astronomers were trying to develop in the 1950s which seemed impossible to calibrate satisfactorily. So it seems that translating Tycho magnitudes into anything other than B, V and R is a waste of time and even these are not excitingly good.

 

My main concern is that since shifting from pm tube UBV photometry to CCD BVRI photometry I can't recognise interesting stars by their colours any more. I asked if there was any quick and easy way to pick out objects likely to be variable. Near V4742 Sgr there's a star with a V-R of about 2.1. There are also some others with V-R over 1 which equates to B-V of about 2+. But there's heavy obscuration all around this area which means these numbers may result largely from reddening. Is H alpha emission strong enough in the case of Miras or other red variables to significantly affect the V-R colour when compared to V-I? This might help a little.

 

I looked at Doug's colour for BD +59 224 and it didn't look much different from Miras we used to measure at Auckland in UBV. Most ranged from B-V 1.5 to 2.5 and U-B -0.5 to 1.0. In some cases there was obviously a blue companion judging by the changes in the colour curves. So these differ from VV Cephei only in that they don't show eclipses. You'd expect about a third of all red variables to fall into this category so that this star is not all that curious. But I'm rather jealous of Doug's ability to get good U-B colours in a CCD system. At one stage I thought a little about trying a U filter with an IR blocking filter on the ST6 which in theory has a marginal sensitivity in the U band. Maybe I'll try this over the summer.

 

Regards,

Stan

----- Original Message -----

From: DWest61506@aol.com

To: Brian.Skiff@lowell.edu ; aavso-discussion@informer2.cis.McMaster.CA ; vsnet-chat@kusastro.kyoto-u.ac.jp

Sent: Thursday, October 10, 2002 5:59 AM

Subject: [vsnet-chat 5555] The curious case of BD+59 224

Brian:
I have some additional photometry for BD+59 224 to report.  Last week I
received a U band filter and I now have my telescope/CCD camera setup
calibrated in UBVRcIc.  I used the standard fields IC 4665 and M44 and the
Henden and Kaitchuck PEP software to derive the transformation coefficients.

On 10/07/2002, under clear skies, I was able to image the BD+59 224 field in
UBV.  Listed below are the results from the observations. For comparison and
check stars I used the stars within the field of BD+59 224.  I converted the
Tycho 2 Bt and Vt magnitudes to UBV using the formulas at
<http://members.aol.com/dwest61506/page32.html>. The results are in table 1.

Table 1 - Magnitudes derived from Tycho 2 Bt and Vt

Star                  Bt          Vt           U          B         U-B        V        B-V    
GSC 4030:591  10.513    10.234    10.21    10.46    -0.25    10.21    0.24    
GSC 4030:427   11.85     10.575    11.63    11.54    0.09    10.46    1.08    
SAO 11690        9.628     9.467     9.32      9.60     -0.29     9.46    0.15    
BD+59 224       11.412     9.646    11.23     10.97    0.25     9.48    1.49    

The flux was determined using MIRA software and the instrumental magnitudes
were transformed into the standard UBV system using the Henden and Kaitchuck
PEP software package.

10/07/2002 2:20 UT  
Photometry using comparison star SAO 11690:

BD+59 224 U-B = 0.34, B-V = 1.84, V = 9.41
GSC 4030:591 U-B = -0.11, B-V = 0.28, V = 10.11
GSC 4030:427 U-B = 0.24,  B-V = 1.21, V= 10.42

Photometry using comparison star GSC 4030:427:

BD+59 224 U-B = 0.19, B-V = 1.71, V = 9.45
GSC 4030:591 U-B = -0.26, B-V = 0.14, V = 10.16
SAO 11690 U-B = -0.44, B-V = 0.02 , V= 9.50

Taking average magnitudes of BD+59 224 from the two comparison stars yields:
U - B = 0.27 +/- 0.1
B- V = 1.78 +/- 0.1
V = 9.43 +/- 0.05
The estimated errors take into account all sources of error.

From SIMBAD I pulled the colors of VV Cep, which are: U-B = 0.37 to 0.44 and
B-V = 1.72 to 1.85.  The similarity in colors of BD+59 224 and VV Cep
support your conjecture that BD+59 224 is a VV Cep type of system.

Regards,
Doug West


In a message dated 9/29/2002 10:13:56 PM Central Daylight Time, Brian.Skiff@lowell.edu writes:

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