bluuebunny/crossref_metadata_2025_split huggingface dataset:
Low-Luminosity Stars: Past and Future
Authors: Reid I.N. 
Published: June 2021

The expression “low luminosity stars” is a descriptive category which spans a wide range of objects, from the oldest stellar remnants in the Galaxy (Wood) through failed stars (Jones, Gould) to the enigmatic MACHOs, discernible not in themselves but only through their effects on others (Bennet). All of these have attracted considerable attention in recent years, and significant progress has been achieved in each case, even if our understanding has failed to keep up with observations. However, it is in the area of brown dwarfs where the most dramatic results have been obtained. The existence of such objects has been predicted theoretically for well over thirty years, but predictions can fail. Thus the discovery of G1229B (Nakajima et al, 1995), an unambiguous substellar-mass object, followed by the detection of lithium in Teide 1 and Calar 3 in the Pleiades (Rebolo et al, 1996) mark a turning point in studies of brown dwarfs. The issue now is not whether they exist, but what are their properties as a class. With that in mind, a number of obvious questions arise.First, what is the most effective method of finding brown dwarfs? Both brown dwarfs and VLM stars have effective temperatures below 2500K. Hence, many surveys concentrated on searching for objects which were very red at near-infrared wavelengths, and the blue JHK colours exhibited by Gl 229B cameas something of a surprise. This should not have been the case, of course, since Tsuji (1964) predicted the presence of methane in such cool atmospheres well before the term ’brown dwarf’ was invented. Current theory, as summarised in these sessions by Tsuji and Burrows, predicts that, as one moves to lower temperatures, grain formation initially drives (J-K) redward, before grains settle below τ ~ 1 and CH4 absorption sets in. Throughout, however, the optical-to-IR colours, straddling the peak in the emergent flux distribution, become progressively redder (Reid, 1994). Those colours therefore offer the most effective means of identifying both GD 165B-like and Gl 229B-like sources - an argument reinforced by the first results from the IJK DENIS survey (Delfosse et al, 1997).
The 2Mass Redshift Survey
Authors: Huchra J. , Tollestrup E. , Schneider S. , Skrutski M. , Jarrett T. , Chester T. , Cutri R. 
Published: June 2021

With the current convergence of determinations of the Hubble Constant (e.g. The Extragalactic Distance Scale, 1997, Livio, Donahue and Panagia, eds.) to values within ±25% rather than a factor of two, and the clear possibility of determining q0 using high redshift supernovae (Garnavich et al. 1998), the major remaining problem in observational cosmology is the determination of Ω — what is the dark matter, how much is there, and how is it distributed?The most direct approach to the last two parts of the question has been to study galaxy dynamics, first through the motions of galaxies in binaries, groups and clusters, and in the last decade and a half, driven by the observation of our motion w.r.t. the Cosmic Microwave Background (CMB) and thenotion that DM must be clumped on larger scales than galaxy clusters if (Ω is to be unity, through the study of large scale galaxy flows.The ratio of the mass density to the closure mass density, Ω, is thought by most observers to be ~0.1-0.3, primarily based on the results of dynamical measurements of galaxy clusters and, more recently, gravitational lensing studies of clusters. In contrast, most theoretical cosmologists opt for a high density universe, Ω = 1.0, based on the precepts of the inflation scenario, the difficulty of forming galaxies in low density models given the observed smoothness of the microwave background radiation, and the observational evidence from the matching of the available large scale flow measurements (and the absolute microwave background dipole velocity) to the local density field. However this last result is extremely controversial—matching the velocity field to the density field derived from IRAS (60μ) selected galaxy samples yields high Ω values (e.g., Dekel et al. 1993) but matching to optically selected samples yields low values (Hudson 1994; Lahav et al. 1994; Santiago et al. 1995). On small scales, the high Ω camp argues that the true matter distribution is much more extended than the distribution of galaxies, so the dynamical mass estimates are biased low.
Archiving Electronic Publications - A Librarian’s Point of view
Authors: Grothkopf Uta 
Published: June 2021

AbstractArchiving electronic journals is complex. There are many questions; Who archives? What is archived? How many copies should be archived. How can one ensure the integrity of electronic documents? How can access be maintained? Technology will provide some answers. Electronic archives will require periodic refreshing and migration to new technology. Many factors remain unknown at this time.
The Hipparcos Double and Multiple Star Solutions
Authors: Mignard F. 
Published: June 2021

AbstractThe Hipparcos Catalogue provides general astrometric and photometric information on double and multiple stars in specific fields of the main Catalogue and detailed data on the components in the various sections of a dedicated annex: the Double and Multiple Systems Annex (DMSA). Overall statistics of these solutions are presented for the 13211 entries of this annex and the different types of solutions are outlined.
New Ages For Old Clusters
Authors: Reid I.N. 
Published: June 2021

A major result of the Hipparcos mission is the availability of accurate parallaxes for a much-increased sample of nearby subdwarfs. On the basis of those data, both Reid (1997-R97) and Gratton et al (1997-G97) have used main-sequence fitting techniques to obtain new estimates of globular cluster distances, deriving significantly larger moduli (by 0.15 to 0.3 mag) for extreme, metal-poor clusters such as M92 and M15. These re-calibrations are not solely the result of the revised parallax data - both D’Antona, Caloi & Mazzitelli (1997 - DCM) and Reid show that similar results can be derived from pre-Hipparcos subdwarf data if the calibrations are not tied exclusively to HD 103095. The longer distance scale leads to a brighter inferred turnoff, and, combined with the latest models (DCM), ages of only 11 to 13 Gyrs - substantially younger than the 16±2 Gyrs proposed by Bolte & Hogan (1992).Recently, Pont et al (1997) have suggested that these revised distances reflect systematic bias in the calibration, notably underestimation of subdwarf abundances. Their distance modulus for M92 ( (m-M)0=14.68) is closer to the Bolte/Hogan value (14.65 mag) than those derived byG97 (14.82 mag) or Reid (14.93 mag). While we believe that Pont et al overestimate the bias, particularly, where high-resolution spectroscopic analyses are concerned (G97, Reid, preprint), there is no question that significant uncertainties remain in the cluster distance calibration. Colours,rather than luminosities, are particularly vulnerable, and a mismatch of 0.01 in (B-V) translates to δ(m — M)0 ~ 0.05 mag.
Astrometric Radial Velocities From Hipparcos
Authors: Dravins D. , Lindegren L. , Madsen S. , Holmberg J. 
Published: June 2021

AbstractSpace astrometry now permits accurate determinations of stellar radial motion, without using spectroscopy. Although the feasibility of deducing astrometric radial velocities from geometric projection effects was realized already by Schlesinger (1917), only with Hipparcos has it become practical. Such a program has now been carried out for the moving clusters of Ursa Major, Hyades, and Coma Berenices. Realized inaccuracies reach about 300 m/s (Dravins et al. 1997).Discrepancies between astrometric and spectroscopic radial velocities reveal effects (other than stellar motion) that affect wavelength positions of spectral lines. Such are caused by stellar surface convection, and by gravitational redshifts. A parallel program (Gullberg & Dravins 1997) is analyzing high-precision spectroscopic radial velocities for different spectral lines in these stars, using the ELODIE radial-velocity instrument atHaute-Provence.
The Absolute Magnitude of the Early-Type MK Standards From Hipparcos Parallaxes
Authors: Jaschek C. , Gómez A.E. 
Published: June 2021

We have analysed the standards of the MK system in the B0-F5 spectral region with the help of Hipparcos parallaxes, using only stars for which the error on the absolute magnitude is ≤ 0.3 mag. The sample stars (about one hundred) were scrutinized for companions and for interstellar extinction. We find that the main sequence is a wide band and that, although in general giants and dwarfs have different absolute magnitudes, the separation between luminosity class V and III is not clear. We conclude that there is no strict relation between luminosity class and absolute magnitude. The relation is only a statistical one and has a large intrinsic dispersion.We have analysed similarly the system of standards defined by Garrison and Gray (1994) separating low and high rotational velocity standards. We find similar effects as in the original MK system.
The Distances and Absolute Magnitudes of Some Well-Known Red Variables
Authors: Wing Robert F. 
Published: June 2021

Distances and absolute magnitudes have been obtained from an early distribution of Hipparcos data for a number of well-known late-type variables. These data were requested in 1981 in order to ensure that these important stars were not excluded from the Input Catalogue on account of their variability or very red color.Measurements were requested for 20 Mira variables, and 14 of these were successfully observed. Of these, the nearest to the Sun were found to be R Leo (at 102 pc), χ Cyg (106), R Cas (107), R Car (128), T Cep (210),and R Aql (211), with formal errors ranging from ±12 to ±57 pc. Mira itself was not considered because the presence of a companion causes an 11-month wobble in its photocenter which is likely to lead to a spurious parallax. The absolute visual magnitudes of Miras at mean maximum range approximately from -2.5 to +2.0 with a clear dependence on spectral type (cooler stars being fainter). This trend is reversed for absolute magnitudes in the near infrared.Results are also given for 10 small-amplitude variables of late type. The nearest of these are L2 Pup (M5 III, 61 pc) and R Dor (M8e, 62pc). The symbiotic star CH Cyg lies at a rather uncertain distance of 268 ± 65 pc.Data were obtained for 23 carbon stars, including the brightest representatives of each of several subgroups. The nearest of these was found to be the SRb variable U Hya, at 162 ± 20 pc. The stars 19 Psc, Y CVn, W Ori, and HD 201626 were all found to be somewhat more than 200 pc away.
On The Mass-Luminosity Relation
Authors: Lampens P. , Kovalevsky J. , Froeschlé M. , Ruymaekers G. 
Published: June 2021

The new Hipparcos parallaxes and photometry are used to determine individual masses and absolute (bolometric) magnitudes for the components of nearby visual binaries with good to very good orbits. The impact on the mass-luminosity relation (MLR) in the range 0 < MBol< +7.5 mag is then evaluated.We selected 335 visual binaries within 50 pc (σπ/π < 10%) for a full error analysis of their orbits by computing the covariance matrix of the orbital elements with Pourbaix’(1994) algorithm. Using ΔHp and π, we estimated fractional and component masses as well as absolute magnitudes with theirrespective errors: 52 binary systems have relative mass errors smaller than 15%. Lutz and Kelker (1973) corrections have been applied to both datatypes. A new relation BC(Hp) as a function of Teff was obtained for the conversion to bolometric magnitudes. A doubly weighted linear regression model was applied next (Babu and Feigelson, 1996): we derived a ”mean” slope 3.82 ± 0.07 and zero point 4.94 ± 0.03 for the MLR, assuming a linear relationship.Conclusions: a) the improvement of the data on masses by Hipparcos is largely quantitative; b) not all systems agree: small fluctuations from a ”mean” MLR are found as expected from evolutionary or abundance effects; c) the break in the slope of the MLR near MBol = +7 cannot be assessed due to a lack of low-mass binaries in our sample.
Towards an Improved Model of the Galaxy
Authors: Holmberg Johan , Lindegren Lennart , Flynn Chris 
Published: June 2021

We use the Hipparcos survey to derive an improved model of the local galactic structure. The availability of parallaxes for all the stars permits direct determination of stellar distributions, eliminating the basic indeterminacy of classical methods based on star counts. Hipparcos gives for the
first time a truly three-dimensional view of the solar vicinity, and a complete, homogeneous and highly accurate set of magnitudes and colours. This means that new techniques can be applied in the treatment of the data which place strong constraints on a model that tries to describe the local Galactic structure. Here we investigate how well a static model of low complexitycan describe the Hipparcos observations.The interpretation of the Hipparcos data is complicated by various observational errors and selection effects that are hard to treat correctly. We do not try to correct the data, but instead use a model and subject this model to the same observational errors and selection effects. A model catalogue is created that can be compared with the observed catalogue directly in the observational domain, thereby eliminating the effects from various biases.Many features in the HR diagram are for the first time seen in field stars thanks to Hipparcos, such as the slanted red giant clump, previously seen in rich old open clusters such as Berkeley 18. This and other features ofthe observed HR diagram are well reproduced by the model thanks to the rather detailed modelling of the joint Mv/B — V distribution. Actually, separate distributions were derived for the three different components, disk, thick disk and halo, using the kinematic characteristics of the components to discriminate between them.
The Metallicity Distribution of Late Type Dwarfs
Authors: Haywood M. , Palasi J. , Gómez A. , Dasgal L. Meillon 
Published: June 2021

The Hipparcos catalogue provides an accurate and extensive sampling of the solar neighbourhood HR diagram. The morphology of this diagram depends on selection criteria of the catalogue such as the limiting magnitude, angular separation and on the characteristics of the stellar populations near the sun (space density, metallicity, star formation rate, etc). Since the Hipparcos data are so accurate, one needs to model precisely the different selection bias and, at the same time, parametrize models of the galactic stellar populations with sufficient flexibility that as much information as possible can be grasped from the catalogue.Comparisons between our model and the Hipparcos catalogue will be presented elsewhere. Since the quantity of information contained in the Hipparcoscatalogue is so important, models ought to be complex, and external contraints, obtained prior to any general comparison with the model, are welcome.A major factor that influences the distribution of the stars in the HR diagram is the metallicity. For the late type stars, the metallicity distribution can be best studied by re-analysing a volume-limited sample of stars from the catalogue.
Hipparcos and Primary Distance Scale Indicators
Authors: Turon C. 
Published: June 2021

The Hipparcos data are providing a dramatic increase, qualitatively and quantitatively, of the basic available distance information. For example, the numbers of stars for which a relative accuracy better than 10 % is available from Hipparcos data and from ground-based data are respectively 22 396and about 1000. Moreover, the range of spectral types and luminosity classes for which precise parallaxes are available is considerably enlarged, including many stars in open clusters and a small number of Cepheids and RR Lyrae. The bottom of the main sequence is populated down to absolute Hpmagnitude 14, including a number of subdwarf stars essential to derive globular clusters distances and ages (Pont et al, 1997a).Finally, the Hipparcos data show how difficult are the calibration of photometric distances and the transformation of relative trigonometric parallaxes to absolute parallaxes. This is illustrated by the comparison of distances given in the last edition of the Catalogue of Nearby Stars (CNS3, Gliese & Jahreiß 1991), which is the best available compilation of stars said to be closer than 25 pc from ground-based data. About a third of them are found by Hipparcos to be (much) further than this limit (Perryman et ai, 1995). A second example is given by the study of (Binney et al, 1997).
The Hyades: Distance, Structure and Dynamics
Authors: Brown A.G.A. , Perryman M.A.C. 
Published: June 2021

The Hipparcos parallaxes and proper motions together provide a consistent picture of the Hyades distance, structure and dynamics. They yield a cluster convergent point motion consistent with the individual trigonometric parallaxes, and together explain the large distance modulus derived from the most recent ground-based proper motion investigations as originating from differences in the space velocity and small systematic effects in the ground-based proper motions. Conversely, the smaller distance modulus generally derived from a variety of ground-based trigonometric parallax programmes originates from systematically larger values of the ground-based parallaxes. Although recent distance determinations to individual objects in the cluster, most notably the results of Torres et al. (1997a, b, c), are in excellent agreement with the Hipparcos trigonometric parallaxes, extrapolation to a mean cluster distance is again affected by systematic effects in the ground-based proper motion studies.The combination of the Hipparcos astrometry with radial velocity measurements from ground-based programmes provides three-dimensional velocities allowing candidate membership selection to be based on 3-dimensional positional and kinematical criteria. A number of new cluster members have been found within 20 pc of the cluster centre. No evidence for systematic internal velocity structure is found; rather, the results are fully consistent with auniform cluster space motion with an internal velocity dispersion of about 0.3 km s-1. Spatial distribution, mass segregation, and binary distributions are consistent with N-body simulations.
Nearby Open Clusters and HR Diagram Calibration
Authors: Robichon N. , Arenou F. , Turon C. , Lebreton Y. , Mermilliod J.-C. 
Published: June 2021

13 clusters have been analysed (Coma Ber, the Pleiades, IC 2602, IC 2391, Praesepe, Alpha Per, NGC 6475, Blanco 1, Stock 2, NGC 6633, IC 4756, NGC 2516 and NGC 3532). Cluster members have been selected using Hipparcos proper motions and parallaxes. The mean cluster parallaxes have been determined using Hipparcos intermediate data (abscissae on the Reference Great Circles) taking into account star to star correlations. Both selection of members and computation of cluster mean parallaxes are described in Mermilliod et al., 1997 and Robichon et al., 1997.For each cluster, a selection of fainter stars in the ‘Base des Amas’ (Mermilliod, 1988), based on photometric data as well as radialvelocities and proper motions when available, has been done. From this selection and the computed mean parallaxes, the location of the 13 cluster sequences in the observational HR diagram is derived very accurately, at least for the closest clusters for which good photometry and small errors on the mean parallaxes are available. Relative positions of cluster sequences cannot only be explained by differences between cluster metallicities. For example, the Pleiades sequence is 0.5 magnitude bellow the Praesepe sequence whereas the adopted metallicities (obtained spectroscopically i.e. whithout any assumption on the helium content) are respectively -0.034 and +0.10.
Struve - Space Astrometry and Photometry Project
Authors: Ilin A.E. , Butkevich A.G. , Chubey M.S. , Gorshanov D.I. , Kanayev I.I. , Kirian T.R. , Kopylov I.M. , Yershov V.N. 
Published: June 2021

The Space Astrometry and Photometry Project Struve is being designed at the Pulkovo Observatory in cooperation with other Russian space institutes. It is expected to be launched before 2010 with a duration of mission of at least 36 months.The main objectives are to extend at milliarcsecond accuracy the Hipparcos satellite reference system to fainter objects including quasars and to get a second epoch for Hipparcos stars. The project Struve, along with the recently suggested project DIVA, will fill the intermediate place between Hipparcos and microarcsecond astrometry. Unlike DIVA, we propose far more extensive astrometric and photometric surveys.We expect an Output Catalogue of 20 million stars (density of about 500 stars per square degree). A sky survey will be complete down to V = 14 (about 15 million stars), and selected objects down to V = 19.5 will be observed within a special program. The proper motions of the Hipparcos stars will be determined with an accuracy of about 0.1 mas/yr. The mean accuracy of star positions in the output catalogue is expected to be 0.6 mas which could be achieved by proper design of the satellite (symmetry, smooth rotation etc.), optics and the micrometer. A properly designed micrometer (with CCD arrays, special processors for image processing and the compression of the data flux to the ground station) will give the possibility of observing all objects of the sky down to a definite limiting magnitude.
Two concerns about the interpretation of the estimates of historical national accounts before 1850
Authors: van Zanden Jan Luiten , Bolt Jutta 
Published: June 2021

AbstractAs contribution to the debate about the interpretation of the process of economic growth before the Industrial Revolution, we discuss two concerns about the currently available estimates of historical national accounts and the way in which these estimates should be interpreted. Firstly, we argue that estimates of the long-term trends of economic growth should make use of all information contained in time series of Gross Domestic Product (GDP henceforth), and therefore use standard regression analysis to establish those trends. Secondly, we point to the problem that the time series of historical GDP are based on very different estimation procedures, which probably affect the outcome in terms of the level of GDP per capita in the period before 1850. Both concerns imply that we do not entirely agree with Jack Goldstone’s views of pre-industrial growth. In particular, his conclusion that growth was cyclical before 1800 is inconsistent with the available GDP estimates, which point to sustained growth, albeit at a very low rate.