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  • 1
    Publication Date: 2018-06-08
    Description: We report on a near-infrared, long-baseline interferometric search for luminous companions to the star 51 Pegasi conducted with the Palomar Testbed Interferometer. Our data is completely consistent with a single-star hypothesis.
    Keywords: Astrophysics
    Type: Astrophysical Journal (Letters)
    Format: text
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  • 2
    Publication Date: 2013-08-31
    Description: The H I, infrared, CO, H alpha and H beta band observations of M51, the prototypical grand-design spiral galaxy, are used to study the consequences of star formation for the distribution of H I and dust. Using the new Very Large Array (VLA) map of 21 cm emission, the Owens Valley Radio Observatory CO mosaic map, and an H alpha imate, new tests were performed with the idea of Tilanus and Allen that the H I is largely a photodissociation product in star-forming regions. It is confirmed that the H I spiral arms are generally coincident with the H II region arms, and offset downstream from the CO arms. The radial distributions of total gas, H alpha and H I surface density have a simple explanation in the dissociation picture. The distributions also demonstrate how the surface density of H I might be related to the star formation efficiency in molecule-rich galaxies. The large width of the H I regions along the arms compared to that of the giant H II regions can be understood in terms of a simple calculation of the expected size of an H I region associated with a typical giant H II region. The longer lifetime of the stars producing dissociating radiation vs. those producing ionizing radiation and the relatively long molecular formation timescale will also contribute to the greater width of the H I arms if stars are continuously forming on the arms. The lack of detailed coincidence of the H I and H II regions along the inner arms has a variety of possible explanations. Two simple tests were performed to probe the origins of the IRAS emission in M51. First, it was found that the infrared excess (IFE) of M51 is 24, suggesting that a substantial fraction of the infrared emission arises from dust heated by photons which do not originate in massive star-formaing regions. Second, radial cuts through the IRAS bands show that at 12, 25, and 60 microns, the arm-interarm contrast of the IRAS emission is substantially less than that of the H alpha emission, providing further evidence for the explanation and for the existence of a broadly distributed dust component. Deconvolved IRAS maps have improved resolution but do not change this finding.
    Keywords: ASTRONOMY
    Type: NASA-CR-188019 , NAS 1.26:188019
    Format: application/pdf
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  • 3
    Publication Date: 2018-06-08
    Description: Interferometrically determined angular diameters obtained at the Palomar Testbed Interferometer (PTI) for 80 giant and supergiant stars are presented in this paper.
    Keywords: Astronomy
    Type: Astronomical Journal
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  • 4
    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: American Astronomical Society 199th Meeting; Washington, DC; United States
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  • 5
    Publication Date: 2011-08-24
    Description: High-resolution images of T Tau and its infrared companion have been reconstructed from near- and midinfrared data collected at the Hale 5-m telescope. The near-infrared (1-5 microns) results were obtained by 2D speckle imaging and the midinfrared (10-20 microns) results were derived from shift-and-add procedures applied to slit scans. The spectral energy distributions of the separated components were constructed from 1- to 20-micron data collected in less than half a year (September 1990 to January 1991). The spectral energy distribution of the optical component (T Tau N) is interpreted as containing two distinct constituents, a photosphere and a surrounding disk of circumstellar material. Measurements at a number of infrared wavelengths over the period December 1985 to January 1991 show a 2-mag color-independent change in the brightness of the infrared component (T Tau S). It is proposed that this may have been caused by an increase in accretion onto T Tau S and model the spectral energy distribution of T Tau S as being dominated by an accretion disk.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 102; 2066-207
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  • 6
    Publication Date: 2011-08-19
    Description: The discovery of a 110-ms pulsar, PSR2127+11, in the globular cluster M15, is reported. The results of nine months of timing measurements place the new pulsar about 2 arcsec from the center of the cluster, and indicate that it is not a member of a close binary system. The measured negative value of the period derivative is probably the result of the pulsar being bodily accelerated in our direction by the gravitational field of the collapsed core of M15. This apparently overwhelms a positive contribution to the period derivative due to magnetic braking. Although the pulsar has an unexpectedly long period, it is argued that it belongs to the class of 'recycled' pulsars, which have been spun up by accretion in a binary system. The subsequent loss of the pulsar's companion is probably due to disruption of the system by close encounters with other stars.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 337; 531-533
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  • 7
    Publication Date: 2011-08-24
    Description: Earlier, using the X-ray satellite ASCA, we had identified the soft gamma-ray burst repeater (SGR) 1806-20 with a persistent X-ray source, AX 1805.7-2025 which is located close to the center of the radio supernova remnant G10.0-0.3. A burst seen by Burst and Transient Source Experiment (BATSE) was shown to be centered on G10.0-0.3. Here we report detailed temporal and spectral analysis of the persistent source. We find that AX 1805.7-2025 is a very compact source, size less than 30 sec in diameter, with a power-law spectrum. The count rate from AX 1805.7-2025 is steady on timescales of minutes, days, and 1 week. Most supernova remnants have extended X-ray emission ascribed to shocked gas. We set an upper limit to an extended X-ray emission both in continuum and line emission. We conclude that an isolated neutron star, most likely a pulsar, powers the radio remnant G10.0-0.3. Finally, we note that the persistent spectrum appears to be less absorbed than the burst spectrum.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 436; 1; p. L23-L25
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  • 8
    Publication Date: 2014-09-16
    Description: Results relating to the following aspects of hydrogen clouds are presented: (1) the vertical distribution of cold H T clouds; (2) possible systematic warming of H T clouds at high absolute values of z; (3) possible increase of the fraction of warm intercloud medium H T with high absolute values of z; and (4) the effect of optical depth on previous H T emission surveys.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 269-273
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  • 9
    Publication Date: 2019-07-13
    Description: During the first few days after explosion, Type II supernovae (SNe) are dominated by relatively simple physics. Theoretical predictions regarding early-time SN light curves in the ultraviolet (UV) and optical bands are thus quite robust. We present, for the first time, a sample of 57 R-band SN II light curves that are well-monitored during their rise, with greater than 5 detections during the first 10 days after discovery, and a well-constrained time of explosion to within 13 days. We show that the energy per unit mass (E/M) can be deduced to roughly a factor of five by comparing early-time optical data to the 2011 model of Rabinak Waxman, while the progenitor radius cannot be determined based on R-band data alone. We find that SN II explosion energies span a range of EM = (0.2-20) x 10(exp 51) erg/(10 M stellar mass), and have a mean energy per unit mass of E/ M = 0.85 x 10(exp 51) erg(10 stellar mass), corrected for Malmquist bias. Assuming a small spread in progenitor masses, this indicates a large intrinsic diversity in explosion energy. Moreover, E/M is positively correlated with the amount of Ni-56 produced in the explosion, as predicted by some recent models of core-collapse SNe. We further present several empirical correlations. The peak magnitude is correlated with the decline rate (Delta m(sub15), the decline rate is weakly correlated with the rise time, and the rise time is not significantly correlated with the peak magnitude. Faster declining SNe are more luminous and have longer rise times. This limits the possible power sources for such events.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN41774 , The Astrophysical Journal (ISSN 2041-8205) (e-ISSN 2041-8213); 820; 1; 33
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  • 10
    Publication Date: 2019-07-13
    Description: We have commenced a multiyear program, the Caltech-NRAO Stripe 82 Survey (CNSS), to search for radio transients with the Jansky VLA in the Sloan Digital Sky Survey Stripe 82 region. The CNSS will deliver five epochs over the entire approx. 270 deg.(exp. 2) of Stripe 82, an eventual deep combined map with an rms noise of approx. 40 proper motion epoch y and catalogs at a frequency of 3 GHz, and having a spatial resolution of 3 inches. This first paper presents the results from an initial pilot survey of a 50 deg.(exp. 2) region of Stripe 82, involving four epochs spanning logarithmic timescales between 1 week and 1.5 yr, with the combined map having a median rms noise of 35 proper motion epoch y. This pilot survey enabled the development of the hardware and software for rapid data processing, as well as transient detection and follow-up, necessary for the full 270 deg.(exp. 2) survey. Data editing, calibration, imaging, source extraction, cataloging, and transient identification were completed in a semi-automated fashion within 6 hr of completion of each epoch of observations, using dedicated computational hardware at the NRAO in Socorro and custom-developed data reduction and transient detection pipelines. Classification of variable and transient sources relied heavily on the wealth of multiwavelength legacy survey data in the Stripe 82 region, supplemented by repeated mapping of the region by the Palomar Transient Factory. A total of 3.9(+0.5%/-0.9%) of the few thousand detected point sources werefound to vary by greater than 30%, consistent with similar studies at 1.4 and 5 GHz. Multiwavelength photometric data and light curves suggest that the variability is mostly due to shock-induced flaring in the jets of active galactic nuclei (AGNs). Although this was only a pilot survey, we detected two bona fide transients, associated with an RS CVn binary and a dKe star. Comparison with existing legacy survey data (FIRST, VLA-Stripe 82) revealed additional highly variable and transient sources on timescales between 5 and 20 yr, largely associated with renewed AGN activity. The rates of such AGNs possibly imply episodes of enhanced accretion and jet activity occurring once every approx. 40,000 yr in these galaxies. We compile the revised radio transient rates and make recommendations for future transient surveys and joint radio-optical experiments.
    Keywords: Astrophysics; Optics
    Type: GSFC-E-DAA-TN41763 , The Astrophysical Journal (ISSN 0004-637X) (e-ISSN 1538-4357); 818; 2; 105
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