Helmut A. Abt

Rotational Velocities of B Stars

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 and and the other lobe of slowly-rotating Ap stars. This is consistent with diffusion theory by Michaud. (3) Using interior models by Bertelli et al. we predicted rotational velocities of giants and found that they agree with observational ones for rigid-body rotation. Combining this with other data, we conclude that if the expansion of post-main sequence stars is a factor of 4, it is in shells. (4) In binaries the primaries have synchronized rotational and orbital motions for periods < 2.4 days. For the A stars studied by Abt & Morrell the limit is 5.0 days. (5) In binaries the orbits are circularized for periods < 1.5 days and for A star < 2.5 days. For binaries of 107.5 — 1010.2 yr the maximum circularized period is 0.0016 A 0.40 days.

The frequency and formation mechanism of B2-B5 main-sequence binaries

Twenty coude spectra were obtained for each of the 74 B2-B5 IV or V stars, and the results of their radial velocities were combined with those of a previous study of 42 similar stars, to examine the frequency and the formation mechanism of these binaries. New improved orbital elements are listed for nine known double-lined and 26 single-lined spectroscopic binaries. It is found that, systems with periods of 0.01 yr to 100,000 yrs, have secondary frequencies that fit the Salpeter (1955) luminosity function (but not the van Rhijn function), indicating that these systems were formed primarily by capture. For systems with periods shorter than 0.01 yr, the separations of components are only a few stellar radii, suggesting that these systems have undergone mass transfer; their secondary masses have no direct information concerning the formation mechanism. 53 refs.

Improved study of metallic-line binaries

Nouvelle etude de la frequence de binaires parmi les etoiles Am a raie metallique classiques et des caracteristiques de ces systemes

What happens to rejected astronomical papers

We studied the histories of the 1039 papers submitted in 1984 to the Pub. A. S.P., A.J., and Ap. J. (first half of 1984) and found that 90% were eventually accepted and published in the initial journals. Of the remainder, two-thirds never appeared in other journals and one-third (32 papers) appeared in a large variety (18) of journals, mostly nondomestic. These numbers do not differ significantly between the three journals but differ drastically from journals in fields other than the physical sciences where the acceptance rates are usually 10%-30% and authors tend to submit rejected papers to other journals rather than to revise them. Key words: publication-reviewing

The future of single-authored papers

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 future. This is contrary to the prediction that they would become extinct.

Rotation and shell spectra among A-type dwarfs.

Rotational velocities for 66 metallic-line and 123 normal AS-Ag IV or V stars are given and used to determine the frequency distributions of equatorial rotational velocities. Those distributions have only a 1.3 percent overlap, which is probably due to a small contamination of the two samples. If so, then the rotational velocity is a necessary and sufficient parameter to detennine whether, within certain spectral type and age ranges, a star will have a well- developed metallic-line or normal spectrum. Among the 35 most rapidly rotating normal stars, eight were found to have shell spectra. Most of the shell stars occur during or just after the overall stellar contraction when the stars have depleted most of their core hydrogen; one shell star has apparently recently contracted to the main sequence. These shell stars seem to be the A-type counterpants of the Be stars. (auth)

Spectroscopic binaries in the Orion Nebula cluster

A search was made for spectroscopic binaries among the 26 brightest members of this very young cluster. Orbital elements are given for four binaries (three known binaries, one newly discovered), and one star is a probable binary. In agreement with published predictions from n-body simulations for binary formation by capture, it is found that the spectroscopic binaries have long periods (median of 20 days), have low-mass companions, are not rotating synchronously with their orbital motions even for a period of 6.5 days, and are probably not concentrated toward the cluster center more than are the massive single stars. The binary frequency is probably normal for a cluster with a high mean rotational velocity. 38 refs.

Do Important Papers Produce High Citation Counts

In honor of the centennial of the American Astronomical Society, we asked 53 senior astronomers to select what they thought were the most important papers published in the Astronomical Journal or Astrophysical Journal during this century. This selection of important papers gives us the opportunity to determine whether important papers invariably produce high citation counts. We compared those papers with control papers that appeared immediately before and after the important papers. We found that the important papers published before 1950 produced 11 times as many citations on the average as the controls and after 1950, 5.1 times as many citations. Of the important papers, 92% produced more citations than the average for the control papers. Therefore important papers almost invariably produce many more citations than others, and citation counts are good measures of importance or usefulness. An appraisal of the 53 papers is that three are primarily useful collections of data or descriptions, 46 are fundamental studies giving important results, and four are both useful and fundamental. The lifetimes of all 53 important papers average 2.5 times longer than for the controls. The ages of the authors of these important papers ranged from 23 to 70, with a mean of 39±11 years, indicating that astronomers can write important papers at any age.

The frequencies of multinational papers in various sciences

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 Factors greater than 1.0. The frequencies of multinational papers ranged from 13% in surgery to 55% in astronomy. Although one can list a dozen factors which might contribute toward multinational papers, I lack the data to test most of those. There are only minor correlations with team sizes and Impact Factors, inadequate to explain the range. There is a larger, but not convincing, dependence upon the fractions of single-author papers and its cause, if real, is unclear. However, the most prominent factor seems to be the nature of the objects studied; if they are usually local (e.g. in one hospital or in one laboratory), the papers tend to be domestic but if most of the objects are available simultaneously to scientists in many countries (e.g. the sky in astronomy or the oceans and the Earth’s atmosphere in geosciences or widespread diseases in the area of infectious diseases or plants and animals widely distributed in biology), the papers are often international. Auxiliary results for 2005 are an average of 5.5 ± 0.3 authors per paper and 6.6 ± 1.0% one-author papers.

Citations to single and multiauthored papers

It is shown that on the average, the number of citations to papers increases linearly with the number of authors. However, if team research takes substantially more time to perform than individual research, the advantage is lost. The larger citation rate for many-authored papers is not due to the higher citation rate for longer papers because they tend to be shorter than few-authored papers: it is also not due to certain more-active fields more multiauthored papers. Longer papers yield substantially larger numbers of citations than shorter papers, but a single long paper still yields fewer citations than the total for several shorter ones of the same combined lengths.