scholarly journals The Use of Praesepe for the Definition of the Lower Part of the Zero-Age Main Sequence

1978 ◽  
Vol 80 ◽  
pp. 277-280
Author(s):  
M. Golay
Keyword(s):  
Main Sequence ◽  
Absolute Magnitude ◽  
Central Star ◽  
Distance Modulus ◽  
Photometric System ◽  
Mass Ratio ◽  
Depth Effect ◽  
Fitting Procedure ◽  
Trigonometric Parallax ◽  
Definition Of

In an attempt to determine the Hyades distance (Golay, 1973), it was assumed that stars of the same “photometric 0m.01 box” (see Golay, 1977a) have the same visual absolute magnitude. The large amount of photometric data in the UBV B1B2V1G photometric system allows a discussion on this hypothesis (Golay, 1977b). We have 60 “photometric 0m.01 boxes”, each containing a central star of known trigonometric parallax and at least one Praesepe star. We select the 16 boxes (Table I) containing single stars or binaries with an estimated mass ratio, a relative probable error < 30% for the parallaxes and a standard deviation for colors <0m.007. The UBV B1B2V1G colors, the indices (B-V), (B2-V1) and the magnitude mVare taken from theSecond Catalogue(Rufener, 1976) and the internal catalogue of the Geneva Observatory. The color index (B-V) is taken from Johnson (1952, 1957), Johnson and Knuckles (1955), the trigonometric parallax from Jenkins (1952, 1963) and Gliese (1969) and the spectral type for Hyades stars from Morgan and Hiltner (1965). The listings of all 0m.01 photometric star boxes in the UBV B1B2V1G system are given by Golay (1977c). The parallax obtained for Praesepe is π(0″.001) = 6.175 ± p.e. 0.1, i.e. a distance modulus (m-M) = 6m.05 and a distance of 162 parsecs. Golay (1977c) published the differences of the distance moduli for pairs of clusters having stars in the same box. The distances of these clusters is given in Table III, assuming a distance of 162 pc for Praesepe. The accuracy of this method is independent of both the distance magnitude and the chemical composition of the stars of a cluster since the stars have to be in the same box as a star with a known trigonometric parallax. The main sequence of Praesepe and a sample of Hyades stars, in the same photometric box with a Praesepe star is given in Table II. The depth effect in Praesepe being very small, the main sequence is very thin and the main sequence fitting procedure is better starting from Praesepe than from the Hyades.

scholarly journals The Luminosity Determination

1995 ◽  
Vol 10 ◽  
pp. 399-402
Author(s):  
A.E. Gómez ◽  
C. Turon
Keyword(s):  
Main Sequence ◽  
Small Volume ◽  
Absolute Magnitude ◽  
Fitting Procedure ◽  
Trigonometric Parallaxes ◽  
The Mean ◽  
The Absolute ◽  
Absolute Magnitudes ◽  
Kinematical Data ◽  
Magnitude Determination

The Hertzprung-Russel (HR) diagram luminosity calibration relies basically on three kinds of data: trigonometric parallaxes, kinematical data (proper motions and radial velocities) and cluster distances obtained by the zero-age main sequence fitting procedure. The most fundamental method to calculate the absolute magnitude is the use of trigonometric parallaxes, but up to now, accurate data only exist for stars contained in a small volume around the sun. Individual absolute magnitudes are obtained using trigonometric parallaxes or photometric and spectroscopic calibrations. In these calibrations the accuracy on the absolute magnitude determination ranges from ±0.m2 in the main sequence to ±0m5 in the giant branch. On the other hand, trigonometric parallaxes, kinematical data or cluster distances have been used to make statistical calibrations of the absolute magnitude. The standard error on the mean absolute magnitude calibrations ranges from ±0m3 to ±0m6 on the mean sequence, from ±0m5 to ±0m7 on thegiant branch and is of about 1mfor supergiants.Future improvements in the absolute magnitude determination will depend on the improvement of the basic data from the ground and space. A brief overview of the new available data is presented. In particular, the analysis of the first 30 months data of the Hipparcos mission (H30) (from the 37 months data of the whole mission) allows to perform a statistical evaluation of the improvements expected in the luminosity determination.

scholarly journals The Occurrence of Different Wolf-Rayet Phases in Massive Close Binaries

1982 ◽  
Vol 99 ◽  
pp. 403-403
Author(s):  
C. Doom ◽  
J.P. De Grève
Keyword(s):  
Binary Systems ◽  
Main Sequence ◽  
Close Binary System ◽  
Close Binary ◽  
Close Binaries ◽  
Mass Ratio ◽  
The Third ◽  
Third Stage ◽  
Definition Of ◽  
Massive Close Binary

In a recent paper (Doom and De Grève, 1981) the remaining main sequence lifetime of the mass gaining component in massive close binary systems was computed. Using results of that paper and the definition of the four important events in the evolution of a massive close binary system (RLOF(M1), RLOF(M2), SN(M1), SN(M2)), four evolutionary stages in the life of the system can be defined: OB+OB, WR+OB, c+OB (or WR+WR) and c+WR. The two possibilities for the third stage depend on the initial mass ratio of the system. The final stage c+c, is not considered here.

scholarly journals RGU Three-Colour-Photometry Towards the North Galactic Pole: Halo-To-Disk Mass Ratio

1977 ◽  
Vol 4 (2) ◽  
pp. 53-54
Author(s):  
R. P. Fenkart ◽  
U. W. Steinlin
Keyword(s):  
Main Sequence ◽  
Rotational Symmetry ◽  
Absolute Magnitude ◽  
Galactic Centre ◽  
Density Functions ◽  
Mass Ratio ◽  
The North ◽  
Disk Mass ◽  
Absolute Magnitudes ◽  
North Galactic

The halo program of the Basel observatory, initiated by Becker in 1965, is based on a three colour photometry in test fields along the circle through the galactic centre and the galactic poles. The more favourable direction of the blanketing vector relative to the main sequence in the two colour diagram for RGU makes it possible to separate at least statistically the disk population and the halo populatior within the interval of absolute magnitudes + 3 ≦ MG ≦ + 8. It is therefore possible to derive density functions for both populations and for different intervals in absolute magnitude for each test direction within the test plane defined above. This allows one to draw isodensity curves in the test plane and, assuming rotational symmetry of the halo, also isodensity surfaces. The last assumption is tested at least locally by test fields with different inclinations towards the test plane (Fenkart, R.P. and Wagner, R., 1975).

scholarly journals The Absolute Magnitude and Stellar Population of a Ba II Star

1973 ◽  
Vol 54 ◽  
pp. 225-228
Author(s):  
R. D. McClure
Keyword(s):  
Stellar Population ◽  
Main Sequence ◽  
Open Cluster ◽  
Absolute Magnitude ◽  
Distance Modulus ◽  
Magnitude Diagram ◽  
The Absolute

A star showing extreme features characteristic of the Ba II stars has been found in the old open cluster NGC 2420. A new colour-magnitude diagram has been constructed for the cluster, and a distance modulus of 11m.7 is obtained by fitting the unevolved main sequence to the zero-age main sequence. The location of the Ba II star is consistent with its being a disc population star of absolute magnitude Mv = −0m.3, mass 1.4 M⊙ and age 2.4 × 109 yr.

scholarly journals CONFERENCE SUMMARY

1991 ◽  
Vol 148 ◽  
pp. 7-12
Author(s):  
J. R. Mould
Keyword(s):  
Short Distance ◽  
Main Sequence ◽  
Absolute Magnitude ◽  
Distance Modulus ◽  
Long Distance ◽  
Ccd Photometry ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Best Value ◽  
Low Weight

It is traditional to begin a review on the subject of the Magellanic Clouds with a discussion of the distance of the Clouds. Feast did this in his introductory remarks to the meeting, and I shall not resist the temptation to reflect a little on this subject. At the Tubingen meeting we gave some thought to a new controversy between a (short) distance modulus of 18.2 for the LMC and the more traditional (Long) distance of 18.7. The short distance was primarily the result of main sequence fitting to LMC clusters resulting from new CCD photometry. A consensus has arisen since that time, and is represented at this meeting by results presented by Walker and Caldwell, and earlier by Reid and Strugnell (1986) and recently by Jacoby et al. (1990), that the best value of (m-M)o is 18.45±0.15 for the LMC (which is also the average of the short and long values). This is obtained, however, by given low weight to (firstly) recent work on the absolute magnitude of RR Lyrae stars based on the Baade-Wesselink technique and (secondly) the aforementioned main sequence fitting results

scholarly journals Star Spots on AR Lac Type Stars

1977 ◽  
Vol 4 (2) ◽  
pp. 397-403 ◽  
Author(s):  
D. M. Popper
Keyword(s):  
Main Sequence ◽  
Light Curves ◽  
Close Binaries ◽  
Good Precision ◽  
Mass Ratio ◽  
Considerable Uncertainty ◽  
Rs Cvn Stars ◽  
Mass Ratios ◽  
Definition Of

There is no generally accepted definition of AR Lac Stars, and the term RS CVn stars is used interchangeably or to refer to a particular subgroup. For the purposes of this discussion I use the term AR Lac stars to refer to detached close binaries showing Ca II emission in at least the cooler component outside eclipse, the hotter component being a main-sequence or subgiant star of spectral type F or G. Most of the systems show irregularities in their light curves as well as period changes. In order to determine whether a system is detached, one must know both the mass ratio and the relative radii. The determination of minimum masses is a fairly straightforward spectroscopic task, and provisional values are available for 22 of the systems, two or possibly three of them being non-eclipsing. All but 3 (AD Cap, RT Lac, RV Lib) have masses of the two components within 30% of each other. Because of appreciable irregularities in the light curves, the radii are subject to considerable uncertainty even when photometry of good precision is available. Nevertheless the 9 systems with very provisional radii all appear to be detached. These all have mass ratios near unity. We may assume, as a working hypothesis, that the other systems with mass ratios near unity are also detached and hence also belong in the AR Lac group. Most of the data referred to are to be found in IBVS 1083.

scholarly journals The Distance and Age of the Globular Cluster M5

1989 ◽  
Vol 111 ◽  
pp. 253-253
Author(s):  
Bruce W. Carney ◽  
David W. Latham ◽  
Rodney V. Jones ◽  
Judy A. Beck
Keyword(s):  
Globular Cluster ◽  
Main Sequence ◽  
Infrared Photometry ◽  
Fitting Procedure ◽  
Trigonometric Parallax ◽  
Cluster Distance ◽  
Echelle Spectroscopy ◽  
Cluster Age

AbstractUsing optical and infrared photometry and echelle spectroscopy of variable V8 in the globular cluster M5, we derive a cluster distance of 6.8 kpc using the Baade-Wesselink method. This agrees with the prediction obtained for the cluster’s metallicity using a sample of 19 field stars studied by us and by Liu and Janes (this volume). It also agrees well with estimates for Mv obtained from statistical parallaxes of field stars. It agrees as well with the main sequence fitting procedure where we have used only HD 103095, the field halo dwarf with the most accurate trigonometric parallax (3% error), and which has a metallicity almost identical to that of M5. The star is also cool, hence unevolved, and is not a binary. Using the luminosity of the cluster’s main sequence, both Yale and Victoria isochrones yield a cluster age of 18 ± 3 Gyrs.

scholarly journals Be Stars as Members of Open Clusters

1987 ◽  
Vol 92 ◽  
pp. 500-502
Author(s):  
A. Feinstein
Keyword(s):  
Main Sequence ◽  
Absolute Magnitude ◽  
Open Clusters ◽  
Distance Modulus ◽  
Be Stars ◽  
Spectral Classification ◽  
Magnitude Diagram ◽  
Color Excess ◽  
Be Star ◽  
The Mean

A list of 124 Be-type stars belonging to 52 open clusters has been compiled. All of them have photometric UBV data, and many of them spectral classification in the MK system. Besides, the cluster's distance modulus and the mean color excess from the member stars are known. Then, we have computed the absolute magnitude and the intrinsic colors of each Be star.The observed color-color diagram (Figure 1) shows clearly that nearly all Be stars appear to be reddened. In Figure 2 is given the color-magnitude diagram, (B-V)o versus Mv, in whicn the ZAMS (Blaauw, 1963) is also included. A few stars to the left of the main sequence belong to the young open clusters: NGC 869, 6167, 6530 and 6611. This effect may be due to wrong correction of the color indices because of abnormal values of the reddening law.

scholarly journals Stellar chemical-abundance gradient in the direction of the South Galactic Pole - preliminary results

1985 ◽  
Vol 106 ◽  
pp. 151-152
Author(s):  
Ch. F. Trefzger ◽  
J. W. Pel ◽  
A. Blaauw
Keyword(s):  
Main Sequence ◽  
Absolute Magnitude ◽  
Photometric System ◽  
Intermediate Type ◽  
Chemical Abundance ◽  
Spectroscopic Analyses ◽  
Program Star ◽  
Effects Of Temperature ◽  
Semi Empirical ◽  
Made In

Using the Walraven VBLUW photometric system, we have studied the metal content of 89 F and G stars in the Galactic South Pole field SA141. Our sample is based on the Basel survey of RGU photometry in Selected Areas, and it contains all stars in SA141 with VJ <14m.5 and (G-R)<1m.15 (spectral types earlier than about G7). The observations were made with the VBLUW photometer and the 90-cm Dutch Telescope at ESO, La Silla.For unreddened intermediate-type stars the VBLUW photometry enables us to separate the effects of temperature, gravity, and metallicity (cf. Lub and Pel, 1977). Since reddening is negligible in SA141, we can therefore determine these three parameters for each program star once the photometric indices are calibrated in terms of Teff, log g, and [Fe/H]. The latter calibration was made in a semi-empirical way, using VBLUW observations of stars with spectroscopic analyses in combination with theoretical colors based on the model spectra by Kurucz (1979). We used the Hyades main-sequence as a zeropoint, adopting [Fe/H] = +0.15 for this cluster.The results in the (V-B)-(B-L) diagram are shown in Fig. 1. This diagram is very sensitive to metallicity, but almost gravity-independent. Fig. 1 indicates that most program stars have metallicities in the range −1 ≦ [Fe/H] ≦ 0. The distribution of the program stars in the gravity-sensitive (V-B)-(L-U) diagram is very narrow, log g =4.2 ± 0.3, which means that these stars are probably all dwarfs, with only very few possible subgiants.The absolute-magnitude calibration was derived by using the data of Cayrel de Strobel et al. (1980) and of Cayrel de Strobel and Bentolila (1983). From their [Fe/H]-catalogue we took all stars with known distances, and within the parameter range of our program stars, to construct an empirical MV - Teff relation. This relation was used to derive distances for the stars in SA141.These distances are plotted against [Fe/H] in Fig. 2. The diagram clearly shows the correlation between distance and metallicity, suggesting for this particular sample a gradient of −0.6 in [Fe/H] over the first 500 pc. Similar values were found in the Basel RGU program (cf. Trefzger, 1981) and by Blaauw and Garmany (1975).

scholarly journals The Absolute Magnitude of the Early-Type MK Standards From Hipparcos Parallaxes

1998 ◽  
Vol 11 (1) ◽  
pp. 566-566
Author(s):  
C. Jaschek ◽  
A.E. Gómez
Keyword(s):  
Main Sequence ◽  
Rotational Velocity ◽  
Wide Band ◽  
Absolute Magnitude ◽  
Interstellar Extinction ◽  
Early Type ◽  
Class V ◽  
Luminosity Class ◽  
The Absolute ◽  
Absolute Magnitudes

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.

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