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  • ASTROPHYSICS  (7)
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  • 1
    Publication Date: 2011-08-19
    Description: IRAS observations of the nuclear bulge of M31 are reported. The 12-micron and 25-micron emission is attributed to circumstellar dust emission from late-type stars, while the 60 and 100-micron emission is attributed to interstellar dust emission. The total input rate of circumstellar gas and dust into the interstellar medium is estimated to be 0.015 solar masses/yr. The mass of dust in the interstellar medium estimated from the far-infared flux is about 1500 solar masses. The color temperature of the far-infrared-emitting dust is 45 K. The time required to accumulate the observed mass in interstellar dust is about 10 million yr. Either supernova-generated winds or star formation can deplete this gas without violating the observations.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 304; 651-656
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  • 2
    Publication Date: 2011-08-18
    Description: A color-magnitude diagram of NGC 147 to an I magnitude of 23 is presented. The stellar population in the outer parts of this elliptical galaxy resembles that of the globular clusters of the Milky Way. Quantitative comparison of the giant branch with those of globular clusters yields a mean metallicity of -1.2 + or - 0.2, making NGC 147 a part of the general correlation between mass and metallicity seen in ellipticals. The giant branch appears to be broad, which suggests a metallicity dispersion. The absence of asymptotic giant branch stars at luminosities above that of the red giant branch tip sets an upper limit of 10 percent for the fraction of stars in this NGC 147 field that have ages less than 12 Gyr. This result contrasts with the situation in some of the related, but less massive, dwarf spheroidal systems. If the choice is made to assume, rather than determine the stellar content of NGC 147, a distance of 630 + or - 50 kpc is derived, similar to that of M31.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 270; July 15
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  • 3
    Publication Date: 2019-07-13
    Description: A ROSAT X-ray observation of the Fornax dwarf spheroidal galaxy is presented. A total of 19 sources are identified, one of which is a probable background galaxy cluster. This is consistent with the number expected due to the extragalactic background. Scaling in luminosity from normal ellipticals and bulges, we would expect to see at most one accreting binary source. This is consistent with our results, and implies that the IMF was not heavily biased towards massive stars. Scaling instead from globular clusters, we would expect eight sources in Fornax in the energy range 10 exp 36 - 10 exp 38 erg/s. We observe none. The low-density environment of the dwarf galaxy evidently does not produce a population of accreting neutron stars through star-star collisions. We place an upper limit of 4 x 10 exp -12 erg sq cm s on any diffuse gas component, corresponding to 10 exp 5 solar mass of gas at 107 K. However, if heated to X-ray temperatures, gas could escape Fornax.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 105; 690; p. 871-874.
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  • 4
    Publication Date: 2019-08-14
    Description: Distances and peculiar velocities for galaxies in eight clusters and groups have been determined by means of the near-infrared Tully-Fisher relation. With the possible exception of a group halfway between us and the Hercules Cluster, we observe peculiar velocities of the same order as the measuring errors of about 400 km/s. The present sample is drawn from the northern Galactic hemisphere and delineates a quiet region in the Hubble flow. This contrasts with the large-scale flows seen in the Hydra-Centaurus and Perseus-Pisces regions. We compare the observed peculiar velocities with predictions based upon the gravity field inferred from the IRAS redshift survey. The differences between the observed and predicted peculiar motions are generally small, except near dense structures, where the observed motions exceed the predictions by significant amounts. Kinematic models of the velocity field are also compared with the data. We cannot distinguish between parameterized models with a great attractor or models with a bulk flow.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 409; 1; p. 14-27.
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  • 5
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    Publication Date: 2019-08-28
    Description: A determination of the luminosity and mass functions is given for field stars at the bottom of the main sequence as the first results from a 320 sq deg survey based on both optical and near-infrared photometry. The luminosity and mass functions are determined with an order of magnitude higher precision than previous studies achieve. No evidence is found for a mass function steepening toward the H-burning limit.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 396; 1 Se
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  • 6
    Publication Date: 2019-07-12
    Description: With a velocity dispersion of 370 + or - 50 km/sec the globular cluster system of M87 is kinematically hotter than the stars in the giant elliptical itself. This is consistent with the clusters' shallower density distribution for isotropic orbits. The mean metallicity of the 27 clusters in the sample analyzed here is no more than a factor of 2 more metal rich than the cluster system of the Milky Way, but considerably more metal poor than the integrated starlight in the field at a radius of 1' from the center of M87. There is no evidence for the existence of young clusters in the system. The mass-radius relation between 1' and 5' required to contain the globular clusters joins on to that required to contain the hot gas around M87.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 93; 53-59
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  • 7
    Publication Date: 2019-07-12
    Description: Two-color CCD photometry of UGC 8508 has resolved the system into stars. The color-magnitude diagram shows blue and red supergiants, the apparent magnitudes of the brightest stars indicate that UGC 8508 lies within 2 Mpc of the adopted 6 Mpc distance of the M 101 group. The galaxy contains a significant color gradient; star formation is confined to the central 1.5 scale lengths (0.8 kpc). UGC 8508 has a central surface brightness intermediate between bursting and quiescent dwarf irregular galaxies.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 98; 732-739
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