J/AJ/109/1055 Globulars of M81 (Perelmuter+ 1995)
The Globular Cluster System of M81
Perelmuter J.M., Racine M.
<Astron. J. 109, 1055 (1995)>
=1995AJ....109.1055P 1995AJ....109.1055P
ADC_Keywords: Galaxies, optical; Clusters, globular; Photometry;
Astrometric data; Morphology
Abstract:
We have obtained photometric BVR, morphological, and astrometric
information on 3774 objects located within a 25' radius of M81. This
catalogue is complete for 15 ≤ V ≤ 21; it is used here to identify
globular cluster candidates in M81 and as a database for a statistical
analysis of the system as a whole. The M81 globular cluster system is
revealed as a strong surface density excess of ∼70 objects within an
11 kpc galactocentric radius. The total population is estimated at N_T
= 210 ± 30 globulars. The spatial, (B-V), and (V-R) distributions
are very similar to those of the Milky Way and of M31. Small but
significant systematic errors in Madore et al.'s [AJ, 106, 2243
(1993)] photometry could be responsible for an overestimate of the
Cepheid distance to M81 [(m-M)0 = 27.8] and we propose a revised
modulus of (m-M)0 = 27.5 ± 0.3. The globular cluster luminosity
function then reaches its maximum at M_V* = -7.5 ± 0.4, as it does
in the galaxy and in M31. There is suggestive evidence that 13 ± 5
objects are globulars seen through the disk of M81; spectroscopy or
high-resolution imaging will resolve this issue. Using the (B-R)0
index to trace [Fe/H], we notice a weak dependence of mean metallicity
on galactocentric distance, as observed in the galaxy and in M31. This
result argues in favour of in situ globular formation during the
continuous collapse and self-enrichment of an early-type spiral host.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table6.dat 74 3774 Catalogue of objects in the M81 field
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- ID Identification number [PR95]
8- 9 I2 h RAh Right ascension (J2000)
11-12 I2 min RAm R.A.
14-19 F6.3 s RAs R.A.
20 A1 --- DE- Declination (always blank)
21-22 I2 deg DEd Declination (J2000)
24-25 I2 arcmin DEm Dec.
27-31 F5.2 arcsec DEs Dec.
33-38 F6.1 yr Epoch Mean epoch of observation
40-44 F5.2 mag Vmag V magnitude
46-50 F5.2 mag B-V B-V color
52-56 F5.2 mag V-R V-R color
57-58 I2 --- N Number of plates object detected upon
60-63 I4 mas/yr pmGlon Proper motion in galactic longitude
65-68 I4 mas/yr pmGlat Proper motion in galactic latitude
70-74 F5.1 --- pmSig *Level of significance of total PM
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Note on pmSig:
The level of significance of the total proper motion, mu/sig_mu,
where mu is the total proper motion = (pmGlon^2 + pmGlat2)(1/2)
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Origin: AAS CD-ROM series, Volume 4, 1995 Lee Brotzman [ADS] 03-May-1995
(End) [CDS] 11-Jul-1995