J/PASP/110/1318 NGC 7789 CCD VI photometry (Gim+, 1998)
The open cluster NGC 7789. II. CCD VI photometry.
Gim M., Vandenberg D.A., Stetson P.B., Hesser J.E., Zurek D.R.
<Publ. Astron. Soc. Pac., 110, 1318-1335 (1998)>
=1998PASP..110.1318G 1998PASP..110.1318G
ADC_Keywords: Clusters, open ; Photometry, CCD ; Photometry, VRI
Keywords: Galaxy: open clusters and associations: individual: NGC 7789 -
stars: evolution
Abstract:
A V, V-I-diagram for the intermediate-age open cluster NGC 7789 has
been derived from CCD observations of more than 15,000 stars within
∼18' of the cluster center. From the brightest giants and blue
stragglers at V∼11 to the faintest lower main-sequence stars that were
observed (at V∼21, MV∼9), the color-magnitude diagram is well
defined. A prominent clump of core helium-burning stars is evident at
V=13.0, and the upper end of the main sequence shows a fairly
pronounced curvature to the red, which is indicative of significant
convective core overshooting. Indeed, comparisons with up-to-date
stellar models show that it is not possible to explain the observed
morphology in the vicinity of the turnoff unless the overshooting is
quite extensive. Interestingly, if sufficient overshooting is assumed
in order to match the main-sequence data, it is not possible to
reproduce the cluster's extended giant branch unless the cluster age
is at least 1.6 Gyr (assuming a metallicity in the range
-0.2≤[FeMH]≤0.0). This, in turn, requires that the cluster have an
apparent distance modulus m-MV≤12.2. Thus, sometime within the past
few hundred million years, the ignition of helium burning in NGC 7789
has switched from a quiescent to an explosive ("flash") phenomenon,
and the length of the cluster's red giant branch has been steadily
increasing with the passage of time since then. From main-sequence
fits to models that have been carefully normalized to the Sun, we
infer a reddening 0.35≤E(V-I)≤0.38.
Description:
Observations for this project were made at the f/5 modified Newtonian
focus of the Dominion Astrophysical Observatory (DAO) 1.8m Plaskett
telescope, by D.R.Z. with the Tek-2 CCD on the nights of 1993
October 10/11, 15/16, and December 16/17 and by M.G. with the
SITe-1 CCD on 1995 October 31/November 1, November 1/2, December
5/6, 6/7, and 8/9. Each detector contains pixels at a scale of
0.53"/pix, yielding a 9x9arcmin2 image size.
Objects:
-------------------------------------------------
RA (2000) DE Designation(s)
-------------------------------------------------
23 57 24 +56 42.5 NGC 7789 = Cl Melotte 245
-------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table.dat 99 15617 VI photometry in the region of NGC 7789
--------------------------------------------------------------------------------
See also:
J/A+A/295/101 : Variable stars in field of NGC 7789 (Jahn+, 1995)
J/PASP/110/1172 : NGC 789 radial velocities (Gim+, 1998)
J/A+A/431/933 : Abundances of NGC 7789 evolved stars (Tautvaisiene+, 2005)
Byte-by-byte Description of file: table.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
2- 6 I5 --- ID [1/15617] Sequential number
8- 15 F8.3 pix Xpos X position (1)
17- 24 F8.3 pix Ypos Y position (1)
27- 33 F7.4 mag Vmag V magnitude
37- 42 F6.4 mag e_Vmag rms uncertainty on Vmag
45- 51 F7.4 mag V-I V-I colour index
55- 60 F6.4 mag e_V-I rms uncertainty on V-I
65- 69 F5.3 --- chi [0.5/8.4] χ value
73- 78 F6.3 --- Sharp [-4/17] DAOPHOT sharpness parameter
(<0 for extended, >0 for cosmic ray)
80- 87 F8.3 --- VarInd [-299/730] Variability index
90- 91 I2 --- Var [0/35] (undefined parameter)
94- 95 I2 --- NV Number of measurements on V band
98- 99 I2 --- NI Number of measurements on I band
--------------------------------------------------------------------------------
Note (1): 1pix=0.0.27"; North is up and East is right. The center of the
panel (4628, 3873) nearly coincides with the cluster center.
--------------------------------------------------------------------------------
History:
Copied at http://webda.physics.muni.cz/ftp/ocl/ngc7789/gim.dat.gz
(End) Patricia Vannier [CDS] 25-Nov-2013