scholarly journals Helium, [Fe/H] Abundances and the HR (Log TEFF, MBol) Diagram With Hipparcos Data of The Four Nearest Open Clusters: Hyades, Coma Berenices, The Pleiades and Praesepe

1998 ◽  
Vol 11 (1) ◽  
pp. 565-565
Author(s):  
G. Cayrel de Strobel ◽  
R. Cayrel ◽  
Y. Lebreton
Keyword(s):  
Main Sequence ◽  
Open Clusters ◽  
Main Sequence Stars ◽  
Spectroscopic Analyses ◽  
Solar Metallicity ◽  
Metal Abundances ◽  
The Mean ◽  
The Moment ◽  
The One ◽  
Best Fit

After having studied in great detail the observational HR diagram (log Teff, Mbol) composed by 40 main sequence stars of the Hyades (Perryman et al.,1997, A&A., in press), we have tried to apply the same method to the observational main sequences of the three next nearest open clusters: Coma Berenices, the Pleiades, and Praesepe. This method consists in comparing the observational main sequence of the clusters with a grid of theoretical ZAMSs. The stars composing the observational main sequences had to have reliable absolute bolometric magnitudes, coming all from individual Hipparcos parallaxes, precise bolometric corrections, effective temperatures and metal abundances from high resolution detailed spectroscopic analyses. If we assume, following the work by Fernandez et al. (1996, A&A,311,127), that the mixing-lenth parameter is solar, the position of a theoretical ZAMS, in the (log Teff, Mbol) plane, computed with given input physics, only depends on two free parameters: the He content Y by mass, and the metallicity Z by mass. If effective temperature and metallicity of the constituting stars of the 4 clusters are previously known by means of detailed analyses, one can deduce their helium abundances by means of an appropriate grid of theoretical ZAMS’s. The comparison between the empirical (log Teff, Mbol) main sequence of the Hyades and the computed ZAMS corresponding to the observed metallicity Z of the Hyades (Z= 0.0240 ± 0.0085) gives a He abundance for the Hyades, Y= 0.26 ± 0.02. Our interpretation, concerning the observational position of the main sequence of the three nearest clusters after the Hyades, is still under way and appears to be greatly more difficult than for the Hyades. For the moment we can say that: ‒ The 15 dwarfs analysed in detailed in Coma have a solar metallicity: [Fe/H] = -0.05 ± 0.06. However, their observational main sequence fit better with the Hyades ZAMS. ‒ The mean metallicity of 13 Pleiades dwarfs analysed in detail is solar. A metal deficient and He normal ZAMS would fit better. But, a warning for absorption in the Pleiades has to be recalled. ‒ The upper main sequence of Praesepe, (the more distant cluster: 180 pc) composed by 11 stars, analysed in detail, is the one which has the best fit with the Hyades ZAMS. The deduced ‘turnoff age’ of the cluster is slightly higher than that of the Hyades: 0.8 Gyr instead of 0.63 Gyr.

scholarly journals Local Stellar Kinematics from RAVE Data – VI. Metallicity Gradients Based on the F–G Main-Sequence Stars

2015 ◽  
Vol 32 ◽  
Author(s):  
O. Plevne ◽  
T. Ak ◽  
S. Karaali ◽  
S. Bilir ◽  
S. Ak ◽  
...  
Keyword(s):  
Main Sequence ◽  
Space Velocity ◽  
Stellar Kinematics ◽  
Main Sequence Stars ◽  
Galactocentric Distance ◽  
Gradient Distribution ◽  
Thin Disc ◽  
Vertical Distance ◽  
Metal Abundances ◽  
The Mean

AbstractWe estimated iron and metallicity gradients in the radial and vertical directions with the F and G type dwarfs taken from the Radial Velocity Experiment Data Release 4 database. The sample defined by the constraints Zmax ⩽ 825 pc and ep ⩽ 0.10 consists of stars with metal abundances and space velocity components agreeable with the thin-disc stars. The radial iron and metallicity gradients estimated for the vertical distance intervals 0 < Zmax ⩽ 500 and 500 < Zmax ⩽ 800 pc are $\text{d}[\text{Fe}/\text{H}]/\text{d}R_{\rm m}=-0.083\pm 0.030$ and $\text{d}[\text{Fe}/\text{H}]/\text{d}R_{\rm m}=-0.048\pm 0.037$ dex kpc−1, and $\text{d}[\text{M}/\text{H}]/\text{d}R_{\rm m}=-0.063\pm 0.011$ and $\text{d}[\text{M}/\text{H}]/\text{d}R_{\rm m}=-0.028\pm 0.057$ dex kpc−1, respectively, where Rm is the mean Galactocentric distance. The iron and metallicity gradients for less number of stars at further vertical distances, 800 < Zmax ⩽ 1500 pc, are mostly positive. Compatible iron and metallicity gradients could be estimated with guiding radius (Rg) for the same vertical distance intervals 0 < Zmax ⩽ 500 and 500 < Zmax ⩽ 800 pc, i.e. $\text{d}[\text{Fe}/\text{H}]/\text{d}R_{\rm g}=-0.083\pm 0.030$ and $\text{d}[\text{Fe}/\text{H}]/\text{d}R_{\rm g}=-0.065\pm 0.039$ dex kpc−1; $\text{d}[\text{M}/\text{H}]/\text{d}R_{\rm g}=-0.062\pm 0.018$ and $\text{d}[\text{M}/\text{H}]/\text{d}R_{\rm g}=-0.055\pm 0.045$ dex kpc−1. F and G type dwarfs on elongated orbits show a complicated radial iron and metallicity gradient distribution in different vertical distance intervals. Significant radial iron and metallicity gradients could be derived neither for the sub-sample stars with Rm ⩽ 8 kpc, nor for the ones at larger distances, Rm > 8 kpc. The range of the iron and metallicity abundance for the F and G type dwarfs on elongated orbits, [−0.13, −0.01), is similar to the thin-disc stars, while at least half of their space velocity components agree better with those of the thick-disc stars. The vertical iron gradients estimated for the F and G type dwarfs on circular orbits are $\text{d}[\text{Fe}/\text{H}]/\text{d}Z_{{\rm max}}=-0.176\pm 0.039$ dex kpc−1 and $\text{d}[\text{Fe}/\text{H}]/\text{d}Z_{{\rm max}}=-0.119\pm 0.036$ dex kpc−1 for the intervals Zmax ⩽ 825 and Zmax ⩽ 1500 pc, respectively.

scholarly journals The Contribution of Hipparcos to the Study of the Stellar Metal-Rich Population in the Solar Neighbourhood

1998 ◽  
Vol 11 (1) ◽  
pp. 566-566
Author(s):  
G. Cayrel de Strobel ◽  
C. Soubiran ◽  
Y. Lebreton
Keyword(s):  
High Resolution ◽  
Interstellar Medium ◽  
Evolved Stars ◽  
Spectroscopic Analyses ◽  
The Galaxy ◽  
Solar Metallicity ◽  
Metal Abundances ◽  
The Mean ◽  
Effective Temperatures ◽  
Absolute Magnitudes

The ‘1996 Edition’ of the Catalogue of [Fe/H] determinations by Cayrel de Strobel et al. (1997, A&A S 124,1) and two recent papers by Castro et al. (1997, AJ Vol.114, N.1) and by Feltzing and Gustafsson (A&A in press) have made possible to increase in the theoretical HR diagram (log Teff, Mbol the number of SMR stars. The SMR Stars of this new enlarged sample had to have reliable absolute magnitudes, coming all from Hipparcos parallaxes, precise bolometric corrections, effective temperatures and metal abundances from high resolution detailed spectroscopic analyses. With the help of an appropriate grid of isochrones computed by Lebreton (1997, Perryman et al. A&A, in press), ‘turn-off ages’could then be attributed to the slightly evolved stars (subgiants) of the sample. The (log Teff, Mbol) diagram constituted by the new sample of SMR stars, shows that the conclusions in a former paper by Cayrel de Strobel (1987, A&AJ 8,141) remain valid: the SMR stars areold stars in spite of their higher than solar metallicity. The result, that metal-rich stars were in the mean old stars, was interpreted in the 1987 paper as due to a more chemical uniformity of the nowadays interstellar medium of the Galaxy with respect of the older much more active interstellar medium.

Distribution and metabolism of corticotropin-releasing factor in the rat

1986 ◽  
Vol 64 (6) ◽  
pp. 683-688 ◽  
Author(s):  
Bernard Candas ◽  
Josée Lalonde ◽  
Maurice Normand
Keyword(s):  
Time Course ◽  
Corticotropin Releasing Factor ◽  
Metabolic Clearance ◽  
Sprague Dawley ◽  
Rapid Injection ◽  
Sprague Dawley Rats ◽  
Significant Difference ◽  
The Mean ◽  
The Moment ◽  
The One

To develop a mathematical model of the distribution and metabolism of rat corticotropin-releasing factor (rCRF), the time course of 125I-labelled rCRF in plasma was measured in male Sprague–Dawley rats (i) following a rapid injection of 24 ng rCRF/100 g body weight (BW), or (ii) following a rapid injection of 424 ng rCRF/100 g BW, or (iii) during an infusion at a rate ranging from 0.28 to0.73 ng rCRF∙min−1∙100 g BW−1. The comparison of the one-, two-, and three-compartment models shows that the two-pool structure fits better to the dynamics of CRF in plasma as measured in each rat. Following a rapid injection the decay curve occurs in a biphasic manner; the early phase of disappearance is 25 times faster than the late one. There is no significant difference between the estimates of the metabolic clearance rate following both amplitudes of injection (0.40 ± 0.06 and 0.48 ± 0.05 mL∙min−1∙100 g BW−1). The volume of the first pool, 16.8 ± 1.1 mL/100 g BW, is four times larger than the plasma volume. It would thus appear that CRF is rapidly distributed from plasma into several tissues which are represented in the first pool of the model. The mean residence time of every CRF molecule in the second compartment, from the moment of secretion to its elimination, is from three to four times longer than in the first one. It stays, on average, between 140 min and 3 h in the system before an irreversible exit. At steady state, the disposal rate represents only 3% of the CRF mass of the first compartment every minute. These results could explain the prolonged effects of CRF on pituitary-adrenocortical secretion.

scholarly journals A preliminary color-magnitude diagram for late-type stars in the solar neighborhood

1959 ◽  
Vol 10 ◽  
pp. 39-40
Author(s):  
O. C. Wilson
Keyword(s):  
Main Sequence ◽  
Star Clusters ◽  
Solar Neighborhood ◽  
Late Type ◽  
Main Sequence Stars ◽  
Individual Values ◽  
Magnitude Diagram ◽  
Trigonometric Parallaxes ◽  
Nearby Stars ◽  
The Mean

Modern photoelectric techniques yield magnitudes and colors of stars with accuracies of the order of a few thousandths and a few hundredths of a magnitude respectively. Hence for star clusters it is possible to derive highly accurate color-magnitude arrays since all of the members of a cluster may be considered to be at the same distance from the observer. It is much more difficult to do this for the nearby stars where all of the objects concerned are at different, and often poorly determined, distances. If one depends upon trigonometric parallaxes, the bulk of the reliable individual values will refer to main sequence stars, and while the mean luminosities of brighter stars are given reasonably well by this method, the scatter introduced into a color-magnitude array by using individual trigonometrically determined luminosities could obscure important features. Somewhat similar objections could be raised against the use of the usual spectroscopic parallaxes which also should be quite good for the main sequence but undoubtedly exhibit appreciable scatter for some, at least, of the brighter stars.

scholarly journals Spectroscopic Analyses of Hot Main Sequence Stars

1986 ◽  
Vol 90 ◽  
pp. 369-380
Author(s):  
Kozo Sadakane
Keyword(s):  
Present Status ◽  
Main Sequence ◽  
Spectroscopic Studies ◽  
Uv Spectra ◽  
Main Sequence Stars ◽  
Visual Region ◽  
Spectroscopic Analyses

AbstractSpectroscopic studies of normal O and early B type stars in the visual region are discussed. Present status of UV spectroscopic analyses of hot normal stars is reviewed. Discussions on a few practical problems in analyses of UV spectra are presented.

scholarly journals Measurements of the Ca ii infrared triplet emission lines of pre-main-sequence stars

2020 ◽  
Vol 72 (5) ◽  
Author(s):  
Mai Yamashita ◽  
Yoichi Itoh ◽  
Yuhei Takagi
Keyword(s):  
Main Sequence ◽  
Open Clusters ◽  
Emission Lines ◽  
Main Sequence Stars ◽  
Low Mass Stars ◽  
Chromospheric Activity ◽  
Low Mass ◽  
Pms Stars ◽  
Infrared Triplet ◽  
Narrow Emission

Abstract We investigated the chromospheric activity of 60 pre-main-sequence (PMS) stars in four molecular clouds and five moving groups. It is considered that strong chromospheric activity is driven by the dynamo processes generated by stellar rotation. In contrast, several researchers have pointed out that the chromospheres of PMS stars are activated by mass accretion from their protoplanetary disks. In this study, the Ca ii infrared triplet (IRT) emission lines were investigated utilizing medium- and high-resolution spectroscopy. The observations were conducted with Nayuta/MALLS and Subaru/HDS. Additionally, archive data obtained by Keck/HIRES, VLT/UVES, and VLT/X-Shooter were used. The small ratios of the equivalent widths indicate that Ca ii IRT emission lines arise primarily in dense chromospheric regions. Seven PMS stars show broad emission lines. Among them, four PMS stars have more than one order of magnitude brighter emission line fluxes compared to the low-mass stars in young open clusters. The four PMS stars have a high mass accretion rate, which indicates that the broad and strong emission results from a large mass accretion. However, most PMS stars exhibit narrow emission lines. No significant correlation was found between the accretion rate and flux of the emission line. The ratios of the surface flux of the Ca ii IRT lines to the stellar bolometric luminosity, $R^{\prime }_{\rm IRT}$, of the PMS stars with narrow emission lines are as large as the largest $R^{\prime }_{\rm IRT}$ of the low-mass stars in the young open clusters. This result indicates that most PMS stars, even in the classical T Tauri star stage, have chromospheric activity similar to zero-age main-sequence stars.

scholarly journals Tidal disruption events on to stellar black holes in triples

2019 ◽  
Vol 489 (1) ◽  
pp. 727-737 ◽  
Author(s):  
Giacomo Fragione ◽  
Nathan W C Leigh ◽  
Rosalba Perna ◽  
Bence Kocsis
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Force ◽  
Main Sequence ◽  
Initial Conditions ◽  
Main Sequence Stars ◽  
Tidal Disruption ◽  
Mean Velocity ◽  
Massive Black Holes ◽  
The Mean

ABSTRACT Stars passing too close to a black hole can produce tidal disruption events (TDEs), when the tidal force across the star exceeds the gravitational force that binds it. TDEs have usually been discussed in relation to massive black holes that reside in the centres of galaxies or lurk in star clusters. We investigate the possibility that triple stars hosting a stellar black hole (SBH) may be sources of TDEs. We start from a triple system made up of three main-sequence stars and model the supernova (SN) kick event that led to the production of an inner binary comprised of an SBH. We evolve these triples with a high-precision N-body code and study their TDEs as a result of Kozai–Lidov oscillations. We explore a variety of distributions of natal kicks imparted during the SN event, various maximum initial separations for the triples, and different distributions of eccentricities. We show that the main parameter that governs the properties of the SBH–MS binaries that produce a TDE in triples is the mean velocity of the natal kick distribution. Smaller σ’s lead to larger inner and outer semimajor axes of the systems that undergo a TDE, smaller SBH masses, and longer time-scales. We find that the fraction of systems that produce a TDE is roughly independent of the initial conditions, while estimate a TDE rate of $2.1\times 10^{-4}{\!-\!}4.7 \, \mathrm{yr}^{-1}$, depending on the prescriptions for the SBH natal kicks. This rate is almost comparable to the expected TDE rate for massive black holes.

Sign in / Sign up

Export Citation Format

Share Document