Thu, 05/06/2021 - 21:32
I used my DSLR (Canon 600D) with 6 comparison stars selected with a wide V and B magnitude ranges. I took 5 minutes of stacked exposures, and the b-v index (tb-tg) I got for g Her before transformation is 1.69. All the comparison stars b-v (tb-tg) values fit the catalogue ones very closely.
However, I found the B-V catalogue index for g Her to be very different among sources:
- 1.67-1.71 in recent PEP observations (LCG).
- 1.52-1.53 in old surveys (VizieR).
- 1.27-1.29 in recent surveys (VizieR).
Would you say g Her is not suitable for DSLR photometry? Why the differences among surveys and empirical data from PEP observers?
Any help is appreciated!
Arturo
Hi Arturo,
I don't know what you mean exactly with old and recent surveys (you need to specify sources not to make general statements because each survey/catalogue is different), but GCPD has the correct values, all the time. These are standard Johnson's B and V magnitudes so much more reliable than anything else you may find.
I bet you took the Tycho derived B-V (from Bt-Vt) among the bluer B-V sources, because Tycho it is known to list such values.
In any case, as you see, your 1.69 is right in the ballpark.
Cheers,
Sebastian
You are right, I'm sorry I was too vague. I searched in the VizieR database after some general searches showing different B-V indexes. As you correctly guessed I found the values from the Hipparcos and Tycho catalogues (1997) to be 1.289 and 1.267. I cannot find the more recent ones I found the other day. My bad.
I must admit I didn't know the GCPD database, and I'm amazed! I'm using it as a reliable source of B-V indexes in the future!
Thank you Sebastian!
Arturo
Hi all, I have a similar problem (finding variable star 'catalog B-V') but wasn't able to figure out how to use the GCPD database. What is the proper link for it and is there a tutorial? And is that still the best place? Thanks, Bob Crumrine, CRR, Rochester, NY.