Affiliation
American Association of Variable Star Observers (AAVSO)
Mon, 06/15/2015 - 18:11
Astronomical Photometry (Henden & Kaitchuck 1990) has a list of regional standard stars for open cluster IC 4665. Is there a more recent collection of "standard" photometry available? Also, does anyone know whether the magnitude quoted for star "K" (HD 161184), a double, is for the primary alone or the primary and secondary together?
Tom
Hi Tom,
HD161184 has an 8.3 and a 9.1 star separated by 1.7 arcsec. The apertures Johnson used were typically about 30arcsec in size, so both members of the pair would have been measured together.
Arne
Hi Tom,
In regards to your first question, the original source of IC 4665 photometry was from Johnson, 1954ApJ...119..181J
Menzies and Marang did additional photometry, including Rc/Ic:
1996MNRAS.282..313M
and then there are isolated papers that have some photometry, such as Cargile and James:
2010AJ....140..677C
but probably not the bright stars that Johnson observed. I did extensive monitoring of the inner 3 square degrees of the cluster with the Bright Star Monitor; I think stars from V=6.8 to about 11 are in VSD. The Johnson calibration was reasonably good, so I'd stick with it unless you have reason to suspect it.
Arne
I am reducing data from the IC4665 cluster to establish transformation for a PEP system. I attach graphs showing the results for Johnson, Menzies and Marang, and Mermilloid & Mermilloid (GCPD) magnitudes. VSD only has magnitudes for only four of the stars I am using. The calculated eVs for the three systems are...
Johnson: -0.043
Menzies: -0.047
Mermilloid: -0.053
Caveat: the Y axis is not actually V-v0. Since the cluster stars are close together and I observed them near transit and my measured V extinction was only 0.16, I here omitted extinction adjustments. An experiment with a simple extinction adjustment produced almost no difference in the BFSL.
Tom
Attached are eV reductions for three nights using both Johnson and Menzies&Marang magnitudes. The last night has some ratty data, and uses 9 stars, while the other two have pretty clean data and each use a different subset of 8 stars. Would you choose Johnson or M&M?
I would average the 3 nights of Menzies.
Gary
I now have four nights of data, summarized below, using both Johnson and Menzies & Marang magnitudes. Nights 57196 and 57224 used 9 stars: A, H, I, J, N, P, R, T, and U in Johnson's nomenclature. Night 57186 omitted star I, while 57187 omitted star T. The amount of scatter concerns me.
Cluster IC 4665 eV calibration
MJD
Menzies eV
R2
Johnson eV
R2
57186
-0.0468
0.94
-0.0430
0.86
57187
-0.0417
0.97
-0.0400
0.84
57196
-0.0492
0.91
-0.0460
0.76
57224
-0.0409
0.91
-0.0377
0.83
mean
-0.0447
-0.0417
I have attached the graphs for all four nights, this time including error bars. The X axis is B-V, while the Y axis is V-v. Again, the cluster stars are close together and were observed near transit, so I did not use the usual V-v0.