Helmut Abt

Helmut Abt
National Optical Astronomy Observatory

Ph.D.

About

399
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9,340
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September 1959 - December 1999
National Optical Astronomy Observatory
Position
  • Astronomer

Publications

Publications (399)
Article
During the 100 years of the International Astronomical Union, the worldwide astronomical publications have grown exponentially, converted almost entirely to English, and changed format from observatory publications to journals to online publications. Observatory publications, conference proceedings, and individual theses have nearly disappeared in...
Article
We have determined spectroscopic orbital elements for 13 systems—10 single-lined binaries and three double-lined binaries. For the three binaries with previously published spectroscopic orbits, we have computed improved or comparable elements. While two systems have relatively short periods between 10 and 19 days, the remaining systems have much lo...
Article
Of 4000 papers published in astronomy and in physics in the past 40 years, 40.3%, and 23.4%, respectively, have not been cited (referenced). However, if we limit this to the final research papers (excluding announcements, book reviews, proposals for funding, and observing time, obituaries, etc.), the fractions are 1.4% and 1.5%, respectively. So vi...
Article
The Chinese first reported the Crab Nebula supernova on 1054 July 5. Ecclesiastical documents from the near east reported it in April and May of 1054. More than 33 petroglyphs made by Native Americans in the US and Mexico are consistent with sightings both before and after conjunction with the Sun on 1054 May 27. We found a petroglyph showing the n...
Article
We learned previously that geniuses and outstanding scientists have peak productivities in their 30s but produce little late in life. This time we consider average astronomers who have completed their careers (25 American Astronomical Society members who died recently) and found that they peak in their mid 40s and did half of their life's important...
Article
The Am, or "Metallic-line," stars have too strong line strengths of the iron peak elements for their temperatures and too weak He, Ca, etc. Michaud showed that the A4-F2 V stars, which occur in the same area of the main sequence as the Am stars, have radiative zones below their photospheres where diffusion acts to push metals upward into the photos...
Article
For 13 journals in six sciences (astronomy, biology, chemistry, engineering, geophysics, and physics) I counted citations in 2017 to 3094 papers published in 2012. It was found that on the average the numbers of citations per paper increased slowly (factor of 1.5) with team sizes but the citations per author are much higher (by an average factor of...
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I explore whether small or large teams produce the most important astronomical results, on average, using citation counts as our metric. I present evidence that citation counts indicate the importance of papers. For the 1343 papers published in A&A, ApJ, and MNRAS in 2012 January-February, I considered 4.5 years worth of citations. In each journal,...
Article
We present the Galactic characteristics of 154 open clusters using the stellar statistics method with data from the WEBDA database. We find that all clusters in our sample are elongated in shape, which indicates that the spherical clusters are stretched out to be ellipsoid as a function of age . By dividing a cluster into a central core and an oute...
Article
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?...
Article
Spectroscopic orbital elements are determined for 15 stars with periods from 8 to 6528 days with six orbits computed for the first time. Improved astrometric orbits are computed for two stars and one new orbit is derived. Visual orbits were previously determined for four stars, four stars are members of multiple systems, and five stars have Hipparc...
Article
I surveyed spectra of 170 bright A-type stars with large rotational velocities (Vsini200kms(-1)). The spectra of 20A stars showed sharp lines of excited Ti II, which is assumed to arise from hot gaseous disks, not interstellar atoms. The fact that the lines come from Ti II and not other singly-ionized iron-peak elements is because among the iron-pe...
Article
For members of the American Astronomical Society, I collected data on their lifetimes from (1) 489 obituaries published in 1991–2015, (2) about 127 members listed as deceased but without published obituaries, and (3) a sample of AAS members without obituaries or not known to the AAS as being deceased. These show that the most frequent lifetimes is...
Article
I explored the use of astronomical monographs used for research. After scanning 135 monographs (excluding conference proceedings and textbooks) listed in 2000–2003 issues of Physics Today and counting citations of them in 2000–2013 in ADS (Astrophysics Data System), I found that 67% of the monographs received fewer than 2 citations per year. The av...
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Full-text available
I scanned the six major astronomical journals of 2008 for all 1589 papers that are based on new data obtained from ground-based optical/IR telescopes worldwide. Then I collected data on numbers of papers, citations to them in 3+ years, the most-cited papers, and annual operating costs. These data are assigned to four groups by telescope aperture. F...
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Astronomers can compute h-indexes using either the Science Citation Index (World of Science) or the Astrophysical Data System (ADS). These two data systems sample different sets of publications.We compare the different results from these and the advantages and disadvantages of each.Because the Hirsch h-index is a steep function of time, their value...
Article
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...
Article
The Discovered Exoplanets Have the Same Orbital Elements as Stellar Systems Helmut A. Abt Kitt Peak National Observatory, Tucson, AZ 85726; abt@noao.edu There are two ways in which planetary masses are formed. One is in debris disks like that that produced the solar system. The other is as separate condensations in stars clusters. We now know...
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Chapter
The history, goals, and capabilities of the Science Citation Index, which is produced by the Institute for Scientific Information, are reviewed. Recent statistics and data about astronomy are given. We address questions such as the importance of self-citations, whether citations really measure importance, and whether citations in different fields c...
Chapter
In the field of astronomy we illustrate the kinds of questions that can be answered with publication studies. For instance, we show that the publication rate is directly proportional to the number of active researchers and not upon technical or scientific breakthroughs. We find that astronomers, at least, are productive of outstanding papers throug...
Article
We wonder whether the exoplanets discovered to date were formed in disk systems, like the Solar System, or like stellar and brown-dwarf companions to stars. We show for large samples that the stellar companions, brown-dwarf companions, and exoplanets have large eccentricities (greater than 0.1 in half of the cases) but in only one of the eight plan...
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Full-text available
The Local Interstellar Bubble is an irregular region from 50 to 150 pc from the Sun in which the interstellar gas density is 10–2-10–3 of that outside the bubble and the interstellar temperature is 106 K. 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 star...
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Starting with the paper by G. Gonz´alez and G. Gonz´alez, 1952, BOTT, 1, 5, 1 in the first volume of the Bulletin, various Tonantzintla astronomers worked for years to find the OB stars that delineate the local spiral arms. Perhaps they became discouraged when the 21 cm radio maps appeared, but they should not have been because the optical data pro...
Article
I congratulate you on this symposium entitled "Highlights of Boletín de los Observatorios de Tonantzintla y Tacubaya", which reviews the publication of the Tonantzintla Observatory that later gave way to its daughter organization INAOE, and the Observatory of Tacubaya of the Universidad Nacional Autónoma de México (UNAM) which later became the Inst...
Article
I explored the growth of astronomical research in the US, UK, and four productive European countries to see if there has been any leveling off. I counted pages in the four major astronomical journals, and corrected for format changes and for contributions from other countries. The four European countries were France, Germany, Italy, and the Netherl...
Article
We explore two ways in which objects of planetary masses can form. One is in disk systems like the solar system. The other is in dense clusters where stars and brown dwarfs form. We do not yet have the instrumental accuracy to detect multiplanet systems with masses like those in solar system; with our present technology from a distant site, only th...
Article
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...
Article
Publication after acceptance in the ApJ is now very fast. The first papers are published in the on-line editions of Part 1 in 23 days after acceptance and 19 days for the Letters. But what about the average interval between submission and acceptance? Such data cannot be found from the papers, but is available only in the editors' logs. I visited th...
Article
We considered 17 open clusters for which published radial velocities studies have been made to search for spectroscopic binaries among the brighter stars. They have log ages of 6.7 to 8.9, with mostly B stars. Some clusters such as the Pleiades have mostly broad-lined stars, indicating large rotational velocities and few binaries, while clusters su...
Article
From a study of the editorial log for 251 manuscripts submitted in 2006, we learn that 6% are rejected, 5% are withdrawn, and 88% are eventually accepted for publication. Of the accepted articles, 30% are reviewed once, 58% twice, and 12% are reviewed 3-5 times. The mean time for the first review is 31 days and for the first revision is 44 days. Th...
Article
The photographic spectra were obtained with the Meinel Cassegrain spectrograph on the Kitt Peak 0.9m telescope. (1 data file).
Article
The Barr Effect is a nonrandom distribution of longitudes of periastron, ω, in spectroscopic binary orbits. Physically one would not expect elliptical binary orbits to show any preferred orientations. Aitken and Struve have shown a preference for 0<ω<90° among 275 elliptical binary orbits of all primary types. Some eclipsing binaries show inconsist...
Article
Two-thirds of the current spectra were obtained with the Meinel Cassegrain spectrograph on the Kitt Peak 0.9m telescope, with a resolution of 2.5Å. The remaining one-third were obtained with the Cassegrain spectrograph (also designed by Meinel) on the Kitt Peak 2.1m telescope, with a resolution of 0.8Å. (2 data files).
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I wondered why there are still slowly rotating (V < 120 km s–1) normal A0-A9 field stars when such stars should have become Ap or Am stars by a diffusion mechanism. My first guess was that this was related to an unusually high binary frequency, but the frequency turned out to be normal, as shown in a paper in preparation. Next, I wondered whether a...
Article
I looked at statistically large samples of references in the Astrophysical Journal and Astronomy & Astrophysics at approximately decade intervals from 1952 to 2009. They show an increase of references to journals from 76% to 90.0% at the expense of references to monographs (down to 3.4%), conference papers (down to 2.6%), in-house papers (down to 1...
Article
Assuming that binaries are formed in three-body interactions in clusters, we wonder whether the process continues after the stars reach the main sequence. We considered the 233 binaries with known orbital elements that are main-sequence members in 69 open clusters, and looked for changes (presumably decreases) in separations or periods and eccentri...
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At any one time, approximately one-quarter of the most rapidly rotating normal A-type dwarfs (V sin i ≥ 200 km s-1) show shell lines of Ti II in the near-ultraviolet. Our observations during 22 years show that the lines appear and disappear on timescales of decades but do not display significant changes within 1 year. This implies that they are not...
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This completes a study of the evolution of binary systems in five open clusters of various ages. Among 21 stars observed in Praesepe, eight are found or confirmed to be spectroscopic binaries and orbital elements are derived, while one more shows long-term binary motion. Among 18 stars observed in the Coma Berenices cluster, five are found or confi...
Article
The 2.1-meter telescope (1964) had the following innovations: (1) an unusually fast f/2.6 primary and f/8 Cassegrain focus that allowed for a small cheaper dome, (2) Ritchey-Chretien coma-free optics, (3) a Pyrex mirror made with the slumping process that was ground and polished in 1.5 years, (4) a flip-top secondary allowing 5-minute conversion be...
Article
Now that all the major astronomical journals are available online and search engines allow astronomers to find pertinent papers regardless of where they are published, do papers in those journals still have a strong tendency to reference papers in the same journals? Current statistics show that all the general astronomical journal papers still have...
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New MK spectral classifications are given for 145 spectroscopic binaries (SBs) with AF primaries because twodimensional types are lacking for more than one-third of the AF SBs with known orbital elements in the current catalog. Compared with the classifications by Morgan, Keenan, and their students, the new classifications give types that are 1.1 ±...
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We sought to determine the maximum age of Trapezium systems by studying possible trapezium systems that were selected independently of their occurrence in H II regions. We started with the unpublished catalog by Allen, Tapia, & Parrao of all the known visual systems having three or more stars in which the maximum separation is less than 3.0 times t...
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We found in the published literature the rotational velocities for 162 B0-B9.5, 152 A0-A5, and 86 A6-F0 stars, all of luminosity classes V or IV, that are in spectroscopic or visual binaries with known orbital elements. The data show that stars in binaries with periods of less than about 4 days have synchronized rotational and orbital motions. Star...
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In this third of three parts of MK classifications of the components brighter than about B = 8 mag in Aitken's Catalogue, new classifications are given for 546 stars. Included in this section are 15 Ap stars, 33 Am stars, 18 stars with composite spectra, three stars with shell spectra, and two SB2s.
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The distribution of individual eccentricities for binaries shows a large scatter between zero (circular orbits) and nearly 1 (highly elliptical), but mean eccentricities show systematic effects. For 296 F0-M5 IV or V primaries with known spectroscopic orbital elements and 482 similar primaries with known visual orbital elements, I collected mean ec...
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As noted by Abt & Morrell, virtually all of the metallic line (Am) and peculiar A (Ap) stars have equatorial rotational velocities less than 120 km s-1, and most of the normal A0-F0 main-sequence stars have equatorial rotational velocities greater than 120 km s-1. However, at all spectral types there are some (10%-20%) of the normal stars that have...
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For 1377 dwarfs and 381 giants of types B and A, we present mean observed projected rotational velocities for normal plus abnormal spectral types combined. For the dwarfs, V sin i is statistically constant at 127 ± 15 km s-1 from B0 V to A5 V. Using the interior models of Bertelli et al., we predict the rotational velocities of the giants. We assum...
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We studied for duplicity the 167 F7-G8 IV or V primaries within 25 pc of the Sun according to their Hipparcos parallaxes and between declinations of -30° and +75°. We obtained an average of 13 coudé radial velocities with an accuracy of ±0.10 km s -1. Combining these measures with published data, we obtained 39 single-lined and 12 double-lined bina...
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It is shown that the hot inner disks around rapidly rotating BA dwarfs (stars conventionally called shell stars) are accreted from the interstellar medium because such disks rarely occur around stars within the heart of the local interstellar bubble, which has less than 10% of the density surrounding it. A working model is one in which stars accret...
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For 391 spectroscopic and visual binaries with known orbital elements and having B0-F0 IV or V primaries, we collected the derived eccentricities. As has been found by others, those binaries with periods of a few days have been circularized. However, those with periods up to about 1000 or more days show reduced eccentricities that asymptotically ap...
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We measured projected rotational velocities for nearly 1100 B stars with these results. (1) They average substantially less than those published in the Bright Star Catalogue and are about one-quarter of the break-up velocities. (2) For the late B stars the deconvolved distribution in V is bimodal; one lobe consists of rapidly-rotating normal stars...
Article
Furenlid & Young showed that in main-sequence B0-B3 stars the Halpha line profiles are distorted, showing shortward absorption evidently due to mass loss. Earlier, others have found evidence of mass loss in UV ionic lines in such stars. Are the radial velocities of B0-B3 stars in the optical region distorted by such effects? We looked at all the 10...
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After a review of what has been learned to date about the Ti II disk lines at lambdalambda3759 and 3761 in the spectra of rapidly rotating A dwarfs, new measures obtained during the past 10 yr are given. They show stars with quasi-periodic variations of 15-30 yr (as in Be stars) and probably longer. The star HR 10 has double disk lines that change...
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In the past there have been many discrepant studies about whether metal-poor (Population II) stars were deficient in binaries or had approximately the same binary frequency as metal-rich stars. We consider here the distributions of periods in five samples of binaries: (1) 138 field halo binaries with low metal abundances ([Fe/H] < −0.30) observed b...
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Stellar line widths yield values of V sin i, but the equatorial rotational velocities, V, cannot be determined for individual stars without knowledge of their inclinations, i, relative to the lines of sight. For large numbers of stars we usually assume random orientations of rotational axes to derive mean values of V, but we wonder whether that ass...
Article
In the fields of physics, astronomy, geophysics, mathematics, and chemistry, the numbers of American papers published depend only on the membership numbers of their scientific societies and not upon improved facilities or instrumental breakthroughs, although those improvements have caused the scientific contents of those papers to be far better in...
Article
The fractions of single-authored papers in four science fields (astronomy, physics, chemistry, and biology) were determined at five-year intervals during 1975–2005. In each case the distribution is best fitted with an exponential function that never reaches zero, implying that single-authored papers will continue to be published in the foreseeable...
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Multinational papers are defined here as ones written by authors who reside in different countries during the course of research. For each of 16 fields of science, I scanned the first 200 papers in 2005 in four major journals publishing original research papers. Those journals produced 40% of all the citations among those journals with Impact Facto...
Article
Including material published previously, I considered all the references listed in the January issues of Astronomy & Astrophysics and the Astrophysical Journal in decade intervals from 1952 to 2006. The re-sults are that journal papers, preprints, and reviews are growing in the frequency in which they are cited, while observatory publications, priv...
Chapter
From a comparison of 1000+ references to 20 papers in four fields of astronomy (solar, stellar, nebular, galaxy), we found that the citation counts in Science Citation Index (SCI) and Astrophysics Data System (ADS) agree for 85% of the citations. ADS gives 15% more citation counts than SCI. SCI has more citations among physics and chemistry journal...
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The impact factor (average number of citations per paper) for the Astrophysical Journal Supplement Series jumped between 2003 and 2004 from 6.247 to 15.231, giving it the world's second highest impact factor for an astronomical journal in 2004. Was this change due to a computing error or to an unusual occurrence? It is shown that it was due to the...
Article
We used the Kitt Peak 0.9m auxiliary feed telescope and the coude spectrograph built for the 2.1m telescope. Also used were a Bausch & Lomb grating (302x361mm2 and 632grooves/mm) and F3KB CCD, yielding 0.11{AA}/pixel and covering 320{AA} centered on 5200{AA}. (2 data files).
Chapter
Among the major changes in astronomical publication during the 20th century are the virtual demise of observatory publication, the growth of conference proceedings, and the continuing dominance of journal publications. The numbers of research papers were found to depend only on the number of researchers and not upon the speed of new detectors and c...
Article
For five sciences (physics, astronomy, geophysics, mathematics, and chemistry) I counted the numbers of papers published annually in 1970-2004 in 5-27 major journals in each field. The totals were divided by the numbers of members in the appropriate American societies, e.g. The American Physical Society. Corrections were made for non-American paper...
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Some object names are in error in Table 1:For:Read:HD 7781HD 89269HD 59950HD 57950HD 133517HD 135517HD 136100HD 136140HD 170099HD 170991HD 222718ABHD 223718AB I very much appreciate Brian Skiff's careful study of my types and the discovery of these errors.
Article
We determined the luminosity function for the secondaries of solar-type stars, based on observations of the 170 F7-G8 IV or V stars with Hipparcos parallax distances within 25 pc and declinations of -30 to +75 deg. Like the Van Rhijn function, it shows an increase in numbers of secondaries down to 0.4 solar masses and then a decline to the 10 extra...
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MK spectral types are given for about 584 stars in A Supplement to the Bright Star Catalogue. These are compared with Hipparcos parallaxes to check the reliability of those classifications. The estimated errors are ±1.2 subtypes, and 10% of the luminosity classes may be wrong.
Article
MK spectral types are given for about 584 stars in "A Supplement to the Bright Star Catalogue" (Hoffleit et al., 1983, Cat. V/36). The spectra were obtained at Kitt Peak in 1983 on Eastman IIaO emulsions, 15% with the Cassegrain spectrograph on the 2.1m telescope and the rest with a Cassegrain spectrograph on the 0.9m telescope. The spectral types...
Article
A total of 1000 new classifications are given for stars brighter than B=8.0mag in the Aitken double star catalog. The classifications supplement 865 classifications obtained in 1981 and 1984. Among the newly discovered stars are 12 new Ap stars, eight Lambda Bootis stars, one Ba II star, and 60 Am stars. A detailed list of the new classifications i...
Article
The spectral types listed here represent about one-third of a program of MK classification of all the Northern (Dec>-30deg) visual components brighter than B~8.0mag. The spectra used were obtained in 1969-1980 with the Cassegrain spectrograph attached to the Kitt Peak No.2 91-cm telescope. The grating spectra have a dispersion of 128{AA}/mm, and ar...
Article
At any one time, about one quarter of the rapidly rotating early-type stars show sharp absorption lines due to hot inner disks (temperatures 10,000 K). The lines appear and disappear on time scales of decades, indicating that they are ephemeral, not primordial. Because no such lines occur around stars with projected rotational velocities less than...
Article
Es apropiado que esta reuni on sobre estrellas dobles y m ultiples sea en honor a Arcadio Poveda, quien ha encontrado muchos resultados sobre estos sistemas. Este texto menciona algunos de esos resultados, as well as como otros aspectos de su investigaci on y de sus logros.
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Se muestra que dos estudios previos sobre la distribuci on de las masas de las secundarias de las binarias espectrosc opicas (Abt & Levy 1976; Duquennoy & Mayor 1991) concuerdan bien si ambos se gra can con la misma escala en las abscisas. Un nuevo estudio de 271 estrellas de la secuencia principal m as tard as que F6 V, realizado con una precisi o...
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From recent measurements of the rotational velocities of 1100 B stars and 1700 A stars, we determined the maximum periods of binaries with fully circularized orbits. Combined with published data, we derived the relation of period (days) = 0.001 age 0.42 (yr). We were able to reproduce the rotational velocities of giants from v sin i of dwarfs only...
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Recent data on duplicity and multiplicity for normal main sequence stars and a variety of classes of stars that have abnormal frequencies are discussed and compared. The occurrence of multiplicity among normal stars is assessed and those classes of stars in which different multiplicities have caused their spectroscopic or evolutionary peculiarities...
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Wilson showed that G8-M1 dwarfs have a range of 0.30 mag in P-V color whereas the color range for earlier stars is 0.12 mag. He attributed the increased range for the later stars to differing hydrogen-to-metal ratios in the temperature region where most of the electrons come from the metals. I explored those stars using Hipparcos parallaxes and pho...
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Some suggestions are given about writing an astronomical paper for an international audience. For each of the parts of a paper (title, abstract, introduction, main text, figures, references) we give ideas on how to write concisely but to be clear yet informative. These are based on my years of being an editor and reading both good and weak papers.
Article
In each of 41 research journals in the physical, life, and social sciences there is a linear relationship between the average number of references and the normalized paper lengths. For most of the journals in a given field, the relationship is the same within statistical errors. For papers of average lengths in different sciences the average number...
Article
We scanned the papers published in the first quarter of 1996 in A&A, AJ, ApJ, Icarus, and MNRAS and counted those that were partly or fully based on new observations from optical ground-based telescopes. We found that 82% of the papers came from telescopes with apertures <4 meters. Then we counted citations since 1996 to those papers and found that...
Article
Stellar line widths yield values of V sin i, but the equatorial rotational velocities, V, cannot be determined for individual stars without knowledge of their inclinations, i, relative to the lines of sight. For large numbers of stars we generally assume random orientations, but is that valid? For eclipsing binaries i is known. For spotted stars we...

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Sandage et al. (PASP, 128, 064202, 2016) showed that the stars in 1.5<Mv<3.5 and 0.6<(B-V)<1.1 really have those luminosities, but think that they are abnormal in some ways. Are they?