73 research outputs found
A uvbyCaHbeta Analysis of the Old Open Cluster, NGC 6819
NGC 6819 is a richly populated, older open cluster situated within the Kepler
field. A CCD survey of the cluster on the uvbyCaHbeta system, coupled with
proper-motion membership, has been used to isolate 382 highly probable,
single-star unevolved main-sequence members over a 20-arcminute field centered
on the cluster. From 278 F dwarfs with high precision photometry in all
indices, a mean reddening of E(b-y) = 0.117 +/- 0.005 or E(B-V) = 0.160 +/-
0.007 is derived, where the standard errors of the mean include both internal
errors and the photometric zero-point uncertainty. With the reddening fixed,
the metallicity derived from the same 278 stars is [Fe/H] = -0.116 +/- 0.101
from m_1 and -0.055 +/- 0.033 from hk, for a weighted average of [Fe/H] = -0.06
+/- 0.04, where the quoted standard errors of the mean values include the
internal errors from the photometric scatter plus the uncertainty in the
photometric zero points. If metallicity is derived using individual reddening
values for each star to account for potential reddening variation across the
face of the cluster, the analogous result is unchanged. The cluster members at
the turnoff of the color-magnitude diagram are used to test and confirm the
recently discovered variation in reddening across the face of the cluster, with
a probable range in the variation of Delta[E(B-V)] = 0.045 +/-0.015. With the
slightly higher reddening and lower [Fe/H] compared to commonly adopted values,
isochrone fitting leads to an age of 2.3 +/- 0.2 Gyr for an apparent modulus of
(m-M) = 12.40 +/-0.12.Comment: WIYN Open Cluster Study LXI; accepted to Astronomical Journal. 11
figures, 2 table
A uvbyCaHbeta CCD Analysis of the Open Cluster Standard, NGC 752
Precision uvbyCaHbeta photometry of the nearby old open cluster, NGC 752, is
presented. The mosaic of CCD fields covers an area ~42' on a side with internal
precision at the 0.005 to 0.010 mag level for the majority of stars down to
V~15. The CCD photometry is tied to the standard system using an extensive set
of published photoelectric observations adopted as secondary standards within
the cluster. Multicolor indices are used to eliminate as nonmembers a large
fraction of the low probability proper-motion members near the faint end of the
main sequence, while identifying 24 potential dwarf members between V=15.0 and
16.5, eight of which have been noted before from Vilnius photometry. From 68
highly probable F dwarf members, we derive a reddening estimate of E(b-y)=
0.025 +/- 0.003 (E(B-V) = 0.034 +/- 0.004), where the error includes the
internal photometric uncertainty and the systematic error arising from the
choice of the standard (b-y), Hbeta relation. With reddening fixed, [Fe/H] is
derived from the F dwarf members using both m_1 and hk, leading to [Fe/H] =
-0.071 +/-0.014 (sem) and -0.017 +/- 0.008 (sem), respectively. Taking the
internal precision and possible systematics in the standard relations into
account, [Fe/H] for NGC 752 becomes -0.03 +/-0.02. With the reddening and
metallicity defined, we use the Victoria-Regina isochrones on the Stromgren
system and find an excellent match for (m-M) = 8.30 +/- 0.05 and an age of 1.45
+/- 0.05 Gyr at the appropriate metallicity.Comment: 37 pages, 11 figures, 4 tables. Accepted to Astronomical Journa
Extended Stromgren Photoelectric Photometry in NGC 752
Photoelectric photometry on the extended Stromgren system (uvbyCa) is
presented for 7 giants and 21 main sequence stars in the old open cluster, NGC
752. Analysis of the hk data for the turnoff stars yields a new determination
of the cluster mean metallicity. From 10 single-star members, [Fe/H] = -0.06
+/- 0.03, where the error quoted is the standard error of the mean and the
Hyades abundance is set at [Fe/H] = +0.12. This result is unchanged if all 20
stars within the limits of the hk metallicity calibration are included. The
derived [Fe/H] is in excellent agreement with past estimates using
properly-zeroed m1 data, transformed moderate-dispersion spectroscopy, and
recent high dispersion spectroscopy.Comment: 14 tex'd pages including 2 tables; 2 separate files with eps figures
Accepted for PASP March 200
vbyCaHbeta CCD Photometry of Clusters. VI. The Metal-Deficient Open Cluster NGC 2420
CCD photometry on the intermediate-band vbyCaHbeta system is presented for
the metal-deficient open cluster, NGC 2420. Restricting the data to probable
single members of the cluster using the CMD and the photometric indices alone
generates a sample of 106 stars at the cluster turnoff. The average E(b-y) =
0.03 +/- 0.003 (s.e.m.) or E(B-V) = 0.050 +/- 0.004 (s.e.m.), where the errors
refer to internal errors alone. With this reddening, [Fe/H] is derived from
both m1 and hk, using b-y and Hbeta as the temperature index. The agreement
among the four approaches is reasonable, leading to a final weighted average of
[Fe/H] = -0.37 +/- 0.05 (s.e.m.) for the cluster, on a scale where the Hyades
has [Fe/H] = +0.12. When combined with the abundances from DDO photometry and
from recalibrated low-resolution spectroscopy, the mean metallicity becomes
[Fe/H] = -0.32 +/- 0.03. It is also demonstrated that the average cluster
abundances based upon either DDO data or low-resolution spectroscopy are
consistently reliable to 0.05 dex or better, contrary to published attempts to
establish an open cluster metallicity scale using simplistic offset corrections
among different surveys.Comment: scheduled for Jan. 2006 AJ; 33 pages, latex, includes 7 figures and 2
table
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