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  • ASTROPHYSICS  (8)
  • 1
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    CCD photometry of Abell clusters. II - Surface photometry of 249 cluster galaxies (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The luminosity of the brightest cluster galaxies remains the best standard candle for observational cosmology. Studies of over 250 relatively nearby clusters show that the luminosity of these objects within an aperture of constant metric diameter has a dispersion of only 0.35 mag. The observations considered by Schneider et al. (1983) were acquired to measure the aperture luminosities of the brightest cluster galaxies. However, the data base, because of its high signal-to-noise ratio and large spatial coverage, allows several other investigations to be performed. In the present investigation, surface photometry of the brightness three galaxies within approximately 250 kpc of the cluster center is presented, taking into account the cores of 83 Abell clusters. The relevance of the photometry to cosmological studies is also discussed. It is found that dynamical friction does play an extremely important role in determining properties of brightest cluster galaxies and cluster morphology.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 268; May 15
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  • 2
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    CCD photometry of Abell clusters. I - Magnitudes and redshifts for 84 brightest cluster galaxies (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The way in which the luminosity of brightest cluster galaxy varies with cluster parameters is investigated in a sample of 84 Abell clusters of moderate redshift and of richness classes in the zero-to-5 range. A photometric system is used which is well matched with the low noise CCD detector employed, as well as to the arrangement of galaxies with different redshifts on a standard system. The data, together with measurements from earlier work which forms a low redshift sample of the 199 brightest cluster galaxies, confirm that the luminosity dispersion in first-rank cluster galaxies is about 0.34 mag. The colors of giant ellipticals have not changed since redshifts of 0.25, and the richness correction is well established at 0.10 mag/Abell richness class. Application of these corrections reduces the luminosity dispersion to 0.29 mag.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 264
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  • 3
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    CCD observations of Abell clusters. IV - Surface photometry of 175 brightest cluster galaxies (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The present data from a consistent body of CCD aperture and surface photometry for the brightest galaxies in 175 clusters from the Abell catalog confirm the dispersion in the aperture luminosities for first-ranked cluster galaxies of about 0.32 mag, as well as the documented trends of luminosity with Bautz-Morgan class and cluster richness. Half of these objects are multiple-nucleus systems; multiplicity is not strongly correlated with cluster morphology or richness, and the fraction of multiples is 2-10 times higher than would be produced by random projection in the cores of Hubble-law clusters. The average distance of the secondary nuclei from the luminosity center of the galaxy is significantly less than the value expected from random projections.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 90; 1648-166
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  • 4
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    Photometry of resolved galaxies. IV - Holmberg I and Holmberg II (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Colors and magnitudes are presented for 279 resolved stars in the Holmberg I dwarf galaxy and 468 resolved stars in Holmberg II. Both systems are Magellanic type dwarf members of the M81-NGC 2403 Group, which lies at approximately 3 Mpc from the Local Group. The photometry was done in the GRI passbands using CCD detectors. Color-magnitude diagrams and luminosity functions are constructed; these are compared with results for several Local Group galaxies and with theoretical work. Holmberg I is found to have a low present star formation rate, while Holmberg II is very active at present.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 286; 159-170
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  • 5
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    Photometry of resolved galaxies. V - NGC 6822 (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Three-color CCD frames of the local group irregular galaxy NGC 6822 have been reduced to GRI photometry for 3475 stars using RICHFLD point-spread function fitting techniques. The data are compared with earlier work on this galaxy, particularly with Kayser (1966) on a star-by-star basis. Color-magnitude diagrams are constructed from the data and compared with both theoretical stellar model tracks and the expected foreground star contamination. A luminosity function for the blue stars is derived; comparison of this luminosity function with those of 10 other irregular galaxies indicates that NGC 6822 has a typical young star population. The stellar birthrate and initial mass function are estimated for this galaxy. The slope at the bright end of the mass function looks similar to recent results for the Galaxy, the Magellanic Clouds, and the irregular galaxy Sextans A. NGC 6822 appears to be presently forming stars at a slower rate for its mass than Sextans A or the Magellanic Clouds.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 60; 507-542
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  • 6
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    The nearby Abell clusters. I - Abell 168 (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: As part of a large program to study the spatial and luminosity distributions of galaxies in the nearby Abell clusters, the results of a photometric study of Abell 168 are presented and compared to the previous results of Dressler (1978). The previous result is confirmed that the faint end of the luminosity function for the galaxies in the central 0.2 sq deg of this cluster is quite flat (alpha = -1.0 in the Schechter formalism). The slope of the faint end appears to be fairly normal if galaxies from a larger region (1 sq deg) are included, but this may be due to a larger than expected contribution of background galaxies. Consequently, the faint end of the luminosity function of galaxies in a 0.2 sq deg region (and possibly also in a 1 sq deg region) centered on A168 is flatter than the 'universal' luminosity function (a Schechter function with alpha = -1.25). Nevertheless, the luminosity functions for both these regions are well fit by Schechter functions. A study of the spatial distribution of galaxies indicates that the radial dependence of the projected surface density is consistent with a power law of slope - 1.01 + or - 0.09.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 91; 697-704
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  • 7
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    The surface-brightness-effective-size relation for elliptical galaxies in the cores of clusters (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Surface photometry of 372 elliptical galaxies has been performed using CCD images of the centers of 97 nearby rich Abell clusters. The strong correlation between surface brightness and effective size, originally found by Kormendy (1977), is clear in the data. Brightest cluster galaxies show much less scatter about the mean relation defined by these data than do lower-luminosity cluster ellipticals, and the slope of the relation is shallower for the brightest galaxies; these two results are tentative, however, because of uncertain selection and environmental effects. When combined with published central velocity dispersions, the photometry yields a relation for brightest cluster galaxies that is in good agreement with the mean relation for elliptical galaxies found by Djorgovski and Davis (1987). Use of the surface-brightness/scale-length relation to measure the lookback luminosity evolution of the stellar content in galaxies is promising.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 94; 1111-111
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  • 8
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    A search for RR Lyrae variables in NGC 147 (1987)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: An analysis of repeated deep CCD observations of a field in the Local Group dwarf elliptical galaxy NBC 147 has resulted in the detection of 34 variable stars. The periods and shapes of light curves obtained for 13 of these variables show nine of them to be RR Lyrae stars. An intensity-averaged phase-weighted-mean g magnitude of 25.15 (+ 0.17 or - 0.15) is found which indicates a distance modulus to NGC 147 of 23.85 (+ 0.22 or - 0.20), or 589 kpc.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 94; 1556-156
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