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Abt H.A.,Kitt Peak National Observatory
Publications of the Astronomical Society of the Pacific | Year: 2010

The US astronomical research output during the past 50 yr has been growing at 6 times the population increase and we wonder whether that ratio can continue. I counted pages of the AJ and ApJ for the past 50 yr, and corrected them for changes in format, foreign input, online contributions, and population increases. For the combined two journals, the American astronomical output is still increasing at a current 128 pages per million people. The same is true for UK contributions to the MNRAS, except that those lag behind the US by 10 yr. For Europe I did not want to dilute the contributions in A&A from the major producers with those of the countries still developing major astronomical centers. Therefore I counted pages for France, Germany, Italy, and the Netherlands (FGIN) only. However, Europeans still publish many of their articles in MNRAS, in particular, and ApJ. Counting FGIN articles in all four journals showed a steady rise but with a 12 yr lag behind the US. We conclude that the astronomical research rates in all three regions have not yet reached a maximum. © 2010. The Astronomical Society of the Pacific. All rights reserved. Source


Abt H.A.,Kitt Peak National Observatory
Astronomical Journal | Year: 2011

The Local Interstellar Bubble is an irregular region from 50 to 150pc from the Sun in which the interstellar gas density is 10-2-10-3 of that outside the bubble and the interstellar temperature is 106K. Evidently most of the gas was swept out by one or more supernovae. I explored the stellar contents and ages of the region from visual double stars, spectroscopic doubles, single stars, open clusters, emission regions, X-ray stars, planetary nebulae, and pulsars. The bubble has three sub-regions. The region toward the galactic center has stars as early as O9.5 V and with ages of 2-4 M yr. It also has a pulsar (PSRJ1856-3754) with a spin-down age of 3.76Myr. That pulsar is likely to be the remnant of the supernova that drove away most of the gas. The central lobe has stars as early as B7 V and therefore an age of about 160Myr or less. The Pleiades lobe has stars as early as B3 and therefore an age of about 50Myr. There are no obvious pulsars that resulted from the supernovae that cleared out those areas. As found previously by Welsh & Lallement, the bubble has five B stars along its perimeter that show high-temperature ions of O VI and C II along their lines of sight, confirming its high interstellar temperature. © 2011. The American Astronomical Society. All rights reserved. Source


Donehew B.,Clemson University | Brittain S.,Kitt Peak National Observatory
Astronomical Journal | Year: 2011

The accretion rate of young stars is a fundamental characteristic of these systems.While accretion onto T Tauri stars has been studied extensively, little work has been done on measuring the accretion rate of their intermediate-mass analogs, the Herbig Ae/Be stars. Measuring the stellar accretion rate of Herbig Ae/Bes is not straightforward both because of the dearth of metal absorption lines available for veiling measurements and the intrinsic brightness of Herbig Ae/Be stars at ultraviolet wavelengths where the brightness of the accretion shock peaks. Alternative approaches to measuring the accretion rate of young stars by measuring the luminosity of proxies such as the Br γ emission line have not been calibrated. A promising approach is the measurement of the veiling of the Balmer discontinuity. We present measurements of this veiling as well as the luminosity of Br γ . We show that the relationship between the luminosity of Br γ and the stellar accretion rate for classical T Tauri stars is consistent with Herbig Ae stars but not Herbig Be stars. We discuss the implications of this finding for understanding the interaction of the star and disk for Herbig Ae/Be stars. © 2011. The American Astronomical Society. Source


Abt H.A.,Kitt Peak National Observatory
Publications of the Astronomical Society of the Pacific | Year: 2016

In 1983 I found that the most productive ages for research astronomers was 40–75 years, contradicting the frequent statement that a scientist’s best work is done before the age of 35. Now most scientists work in small to large teams, unlike the individual research usually done previously. How has that affected the productive careers of astronomers? A new study of 14 recent Russell Lecturers shows a peak in productivity at age 33 and more than half that peak during 25–56 years, in agreement with results in other sciences. Nevertheless, 33% of their best work was done after the age of 50 years. © 2016. The Astronomical Society of the Pacific. All rights reserved. Source


Abt H.A.,Kitt Peak National Observatory
Scientometrics | Year: 2012

The Hirsch h-index is widely used to measure a researcher's major publications. It has the advantage of being easy to compute. However, it increases steeply with time and therefore does not allow a comparison of young and mature researchers. We find that if the h-index is divided by the number of decades since publication of the researcher's first paper, the result is statistically constant with age. Then the resulting index can be compared for young and old researchers. Its accuracy is the same as that of the h-index and is as easy to compute as the h-index. © 2011 Akadémiai Kiadó, Budapest, Hungary. Source

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