Stars In Pleiades Research Articles

An infrared search for low-mass companions of stars near the sun

Using a CCD camera on the IRTF telescope on Mauna Kea, a search was conducted for low-mass companions to stars in the solar neighborhood. The K band (2.2 microns) survey includes 55 condidates closer than 12 pc, as well as eight stars in the Pleiades star cluster. Due to the saturation of the primary star image, the survey was insensitive to companions within about 2 arcsec of the primary star. The survey detected a single low-mass candidate object, a companion to the star Gliese 569, which lies near or below the hydrogen-burning mass limit and resembles extremely low-mass stars similar to VB 10 and LHS 2924.

Interstellar matter near the Pleiades. III - A search for H2 2.4-micron vibration-rotation emission

view Abstract Citations (2) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS IInterstellar Matter Near the Pleiades. III. A Search for H2 2.4-Micrometer Vibration-Rotation Emission White, Richard E. Abstract Observations at 20 positions near five Pleiades stars yielded upper limits on H2 υ = 1-0 Q branch emission in the range (2.6 - 7.2)×10-5erg s-1cm-2sr-1. Corresponding limits on the column density in J = 1-5 of υ = 1 range from (1.3 - 3.7)×1015cm-2. Interpretation in terms of gas fluorescing and dissociating as it flows past the stars yields corresponding H2 density limits 400 - 1100 cm-3, values consistent with prior indirect estimates. An alternative interpretation in terms of collisional excitation yields less stringent limits. Publication: The Astronomical Journal Pub Date: July 1988 DOI: 10.1086/114797 Bibcode: 1988AJ.....96..145W Keywords: Emission Spectra; Hydrogen; Interstellar Gas; Interstellar Matter; Molecular Clouds; Pleiades Cluster; Gas Temperature; Line Spectra; Molecular Gases; Photodissociation; Astrophysics; INTERSTELLAR: MATTER; INFRARED: SOURCES; CLUSTERS: OPEN full text sources ADS | data products SIMBAD (6) Related Materials (5) Part 1: 1984ApJ...284..685W Part 2: 1984ApJ...284..695W Part 4: 1993ApJ...409..234W Part 5: 2001ApJS..132..253W Part 6: 2003ApJS..148..487W

The Iron Abundances, [Fe/H] in the Four Nearest Open Clusters: Pleiades, Ursa Major Stream, Coma Berenices and Hyades

Iron abundances, [Fe/H] have been studied in G and K dwarfs of the four nearest clusters. With the exception of the Pleiades stars which are all fainter than the 10th magnitude, the observational material consists of high resolution, high S/N spectra taken at the coudé Reticon spectrograph of the Canada, France Hawaii Telescope. The Hyades is the only cluster with a significative overmetallicity with respect to the Sun.

Interstellar extinction in the direction of the Merope dark cloud in pleiades

The dependence of interstellar extinction on distance in the direction of the dark cloud south of Merope is determined using photoelectric photometry of 93 stars in the Vilnius photometric system. The cloud front edge is detected at 120–130 pc from the Sun and the distance of the Pleiades cluster is found to be 127 pc. Mean extinctionAV in the Merope cloud is of the order of 1.0 mag. There is no evidence of extinction at distances exceeding the Merope cloud distance. Variable extinction method yieldsR=AV/EB-V=3.6, while the maximum polarization wavelength method gives the value 3.4. Some Pleiades stars are suspected to be unresolved binaries.

Colors of reflection nebulae. III - Ultraviolet scattering by small particles in reflection nebulae associated with 17, 20, and 23 Tauri

New surface brightness measurements in the reflection nebulae associated with the Pleiades stars 17, 20, and 23 Tau have been carried out with the IUE satellite. Each nebula was observed at two angular offsets south of the respective illuminating star. At the larger offsets (40, 40, and 60 arcsec respectively) each nebula exhibits a flux distribution which rises much more steeply with decreasing wavelengths than the corresponding stellar spectrum. At the smaller offsets (20 arcsec) the nebular spectra are more similar to those of the stars and fail to show the steep rise at wavelengths less than 2200 A. Independent observations of interstellar absorption lines as well as theoretical arguments by several previous authors lead to a model wherein the reflection nebulosity near the Pleiades stars is caused by a thin sheet of interstellar matter in front of the stars, at an approximate distance of a few x 10 to the -2nd pc. In the context of such a model the nebular spectra obtained near 17, 20, and 23 Tau can be understood only if the phase-function asymmetry of scattering declines with decreasing wavelengths throughout the spectral range. This result indicates that the role of scattering in the UV by particles in the 10 to the -6th cm size range appears more important than is generally recognized by current models.

ACTIVE-REGION PLAGES AND THE HYADES ANOMALY ?

ABSTRACT The Hyades are known to differ in their photometric properties (Crawford 1969; Campbell 1984) and spectral properties (Rose 1984) from field stars of similar metal abundance. Using spectra of solar plages, it is demonstrated that the Hyades spectral anomalies are caused by excess emission from magnetic regions (plages) on the surfaces of these cluster stars. It is further speculated that the Hyades photometric anomalies arise from the same cause, but photometric data on solar plages necessary to resolve this issue are not available. The Pleiades stars and a few extreme emission stars show similar spectral anomalies, but of such magnitude to indicate that plages on Pleiades stars have higher surface brightnesses than on the sun and do not merely cover a larger fraction of the stars.

Optical and infrared photometry of late-type stars in the Pleiades

view Abstract Citations (142) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optical and infrared photometry of late-type stars in the Pleiades. Stauffer, J. R. Abstract New optical photometry has been obtained for 130 stars in the Pleiades fainter than than V approximately equal to 10 mag. New infrared photometry for 35 of those stars has also been obtained. Analysis of the optical data indicates that the photometric binary frequency for late-type stars in the cluster is 26 percent. That frequency is consistent with both the binary frequency for field G stars derived by Abt and Levy (1976) and the photometric binary frequency for high-mass stars in the Pleiades derived by Bettis (1975). The latter result indicates that binary frequency is nearly independent of the mass of the primary star over the range of M/solar mass between 0.4 and 4.0. The late G and K stars in the Pleiades fall systematically below a nominal main sequence derived from photometry of Hyades and Praesepe stars. Evidence is presented to ascribe that displacement to a metallicity difference between the Pleiades and Hyades stars, to slight IR excesses for the late-type Pleiades stars, and to an incorrect calibration of the cluster differential distance moduli. If the V approximately equal to 12-13 mag Pleiades stars are forced to lie on the zero-age main sequence, the Vandenberg et al. (1983) isochrones suggest a contraction age for low-mass stars in the Pleiades of slightly more than 100 million years. The difference between the nuclear age and the contraction age of the Pleiades would then be greater than a few times 10 million years, in agreement with the age spread of star formation estimated from rotational velocity data presented elsewhere. Publication: The Astrophysical Journal Pub Date: May 1984 DOI: 10.1086/161985 Bibcode: 1984ApJ...280..189S Keywords: Astronomical Photometry; Infrared Astronomy; Infrared Photometry; Late Stars; Pleiades Cluster; Star Clusters; Stellar Evolution; Binary Stars; G Stars; K Stars; Pre-Main Sequence Stars; Stellar Flares; Variable Stars; Astronomy full text sources ADS | data products SIMBAD (102) GCPD (1)

X-Ray Variability of Stars

Most stars emit X-rays. The hot X-ray emitting gas is not gravitationally bound to the star, but is magnetically confined in loops. It is generally assumed that rotation in convective stars relates to magnetic field generation. The X-ray intensity correlates with the rotation rate of the star.Most stars are known to be highly variable in X-ray emission. X-ray flares with rise times of tens of seconds and decay times of tens of minutes to hours are seen in the red dwarf flare stars, in the RS CVn stars, in the Hyades and Pleiades star clusters. In addition, many X-ray sources have been found which probably relate to very young stars, prior to the start of hydrogen burning (pre-main sequence stars).Some of the previously known so-called "fast X-ray transient sources" are identified with RS CVn stars. They represent the largest known increase in X-ray flux, indicating volume emission measures for the hot plasma which may be a million times that of the largest solar flare.In this review I will discuss the observational evidence of X-ray variability obtained so far and give some of the observed properties of red dwarf flare stars and RS CVn stars. A full scale theoretical interpretation of the flare mechanism does not exist for solar flares, let alone for the stellar flares. Stellar flare observations, however, may help to solve the problem.

THE PHOTOMETRIC VARIABILITY OF SOLAR-TYPE STARS. III. RESULTS FROM 1981-82, INCLUDING PARALLEL OBSERVATIONS OF THIRTY-SIX HYADES STARS.

ABSTRACT A photometric survey of main-sequence stars in the Pleiades, Hyades, and Malmquist Field, to investigate variability among solar-type stars, had been continued at Cloudcroft Observatory for a second season. Possibly six of 40 Pleiades stars, two (possibly six) of 49 Hyades stars and possibly four of 42 stars in the Malmquist Field are found to be variable. Parallel observations of Hyades stars were obtained also at Lowell Observatory. These measurements, which achieved better precision, reveal significiant variations in eleven (possibly 16) of 36 Hyades stars, all of spectral type F7 V-K2 V. Agreement between the two surveys is acceptable. The two seasons of the Cloudcroft survey show that changes in the mean annual brightness of the Hyades stars accompany changes in the amplitude of their short-term variability, in the sense that a star tends to become fainter as its variability increases and vice versa. Color effects are absent.

Lithium abundance and age spread in the Pleiades

view Abstract Citations (158) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Lithium abundance and age spread in the Pleiades. Duncan, D. K. ; Jones, B. F. Abstract Surface lithium abundance, a parameter which usually decreases with age in late-type stars, has been determined for Pleiades stars as cool as T(e) approximately 4700 K and Hyades stars as cool as T(e) approximately 5000 K. A large abundance spread is seen among the coolest Pleiades stars, consistent with their having been formed over an interval as long as 0.4 x 10 to the 9th yr, several times longer than the nuclear age of the cluster. Observations of the strength of the Ca II H and K line emission in three of the Pleiades stars also indicate a significant spread in age. Some Pleiades stars as cool as T(e) approximately 5200 K have primordial Li abundances, in conflict with the predictions of pre-main-sequence stellar evolution calculations, indicating that such calculations probably overestimate the importance of convection. Publication: The Astrophysical Journal Pub Date: August 1983 DOI: 10.1086/161233 Bibcode: 1983ApJ...271..663D Keywords: Abundance; Lithium; Pleiades Cluster; Star Clusters; Stellar Evolution; Emission Spectra; Line Spectra; Stellar Temperature; Astrophysics full text sources ADS | data products SIMBAD (58)

Contracting stars in the Pleiades

Contracting stars in the Pleiades

THE PLEIADES AND THE ZERO-AGE MAIN SEQUENCE.

ABSTRACT New four-color uvby observations of the Pleiades are used to calibrate the ZAMS in the spectral range A2 to F5. Although the Pleiades Co versus (b - y)o calibration is in good agreement with the ZAMS calibration presented by , its versus (b - y)o relation shows a systematic difference from his values. This difference is ?o be caused by the higher mean rotational velocity of the Pleiades stars in comparison to field stars. Key words: zero-age main sequence (ZAMS) - uvby photometry

Slow flare in Pleiades

In the course of observations of Pleiades on the 40'' Schmidt telescope of Byurakan Observatory, one slow and two rapid flares were detected in star No. 103. The rise time to the maximum of the flare was ~40 min and the total duration was about 5 h. The brightness magnitudes and photographs of the flare are shown. A statistical analysis of a number of pre-maximum images of flare stars in Pleiades and Orion, taken with different exposures, was carried out. The slow flare stars in Orion and Pleiades are compared. (auth)

Observations of Highly Eccentric Orbits in the Pleiades Cluster

view Abstract Citations (3) References (3) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of Highly Eccentric Orbits in the Pleiades Cluster Jones, Burton F. Abstract New relative proper motions have been determined for fifty-two Pleiades stars on plates taken with the 40-inch refracting telescope at Verkes Observatory, which have a time baseline of up to 66 years. These motions show that stars at distances greater than 20 minutes of arc from the center of the cluster have internal motions that are almost completely in a radial direction, an observation which indicates that these stars are in highly eccentric orbits. Publication: The Astrophysical Journal Pub Date: February 1970 DOI: 10.1086/180492 Bibcode: 1970ApJ...159L.129J full text sources ADS |

Dwarf M Stars in the Pleiades.

Dwarf M Stars in the Pleiades.

The Color-Magnitude Diagram of the Pleiades Cluster. II.

Two- or three-color photographic and photoelectric photometry of virtually all the known members of the Pleiades cluster is given. The photographic photometry was done on plates taken with the 13-inch telescope, while the photoelectric work was done with the 21- and 42-inch reflectors of the Lowell Observatory. We believe that a number of the stars that were previously thought to be members of the Pleiades are actually not members. We find a total of 262 members and 27 probable members brighter than V = 16. No white dwarfs were found. They would have been found if they had been brighter than = 11.8. A sudden increase in the width of the main sequence is observed at V = 12.0. This scatter may be associated with the probable fact that the fainter stars are still in the process of gravitational contraction. A "flare" of one faint Pleiades star was observed, and 5 other faint stars are thought also to be "flare" stars. It is suggested that the "flare" activity might be connected with the process of gravitational contraction of young late-type stars.

Some polarization measurements in the Pleiades and Orion regions.

view Abstract Citations (2) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Some polarization measurements in the Pleiades and Orion regions. Hall, John S. Abstract The light from 23 stars in the Plejades cluster has been examined photoelectrically for polarization with the Ritchey- Chretien reflector. One star in this group, HD 23512, is an 8.3 magnitude Ao star with large color excess which Binnendijk had cited as a star of special interest. Binnendijk's results1 and Eggen's data2 indicate that some of the other stars chosen for observation are space reddened. Measures of HD 23512 made on three nights indicate a polarization of 2.2 per cent and a plane of polarization at 1220.1 This angle is similar to those found, for other nearby stars in the Taurus region. None of the other Pleiades stars show positive evidence of polarization, despite the fact that some are within a few minutes of arc of the highly reddened star. Both the radial velocity and proper motion of this star indicate that it is a member of the cluster. P. W. Merrill was kind enough to examine a low-dispersion spectrogram of it, secured in the photographic region, and found it to be a rather ordinary main-sequence A-type star. Its distance of about a hundred parsecs makes it the nearest star known to exhibit polarization. Markowitz has secured a number of photographs of this region through calcite. His polarization measurements, which are still in progress, include stars of the 15th visual magnitude. An attempt to measure polarization in the light of the members of the Trapezium in the spring of 1949 revealed that the Orion nebula (NGC 1976) is polarized. A micrometer, later attached to the guiding telescope of the ~o-inch, made it possible to explore this nebula in some detail. The area of the sky admitted to the cathode of the pliotomultiplier at any one time Was 380 square seconds of arc. Preliminary measures made on three nights show that the plane of polarization consistently points toward the Trapezium as the source of light. The area so far observed which shows most polarization is 2' due west of HD 37022, where the value is slightly less than 4 per cent. Since the Trapezium stars show little or no polarization it seems probable that the polarization of the reflected or scattered light is not substantially modified as it comes through the nearer regions of the nebula. The reddened,B8 star, HD 37061, just north of the Orion nebula is polarized 1.6 per cent at 1530. This star is imbedded in bright nebulosity. Polarization measurements in the Orion region are to be continued and an attempt will be made to make them in different spectral regions. I.Ann. Stw. Leiden `9, Part II, 1946. 2.Ap. J. iii, 8i, 1950. 3.Pub. U. S. Naval Obs. 17, Part II, 1950. U. S. Naval Observatory, Washington, D. C. Publication: The Astronomical Journal Pub Date: April 1951 DOI: 10.1086/106491 Bibcode: 1951AJ.....56...40H full text sources ADS | data products SIMBAD (4)

Photoelectric Studies. II. Color-Luminosity Array for Members of the Pleiades Cluster.

view Abstract Citations (22) References (5) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photoelectric Studies. II. Color-Luminosity Array for Members of the Pleiades Cluster. Eggen, Olin J. Abstract Magnitudes and colors of 77 Pleiades stars have been determined with a photomultiplier photometer attached to the Lick Observatory 12-inch refractor. With the exception of known visual double stars and a few stars in congested regions, the 77 stars observed include all those which are certainly cluster members and brighter than photographic magnitude 11.0. On the basis of the deduced color4uminosity array the following results have been obtained: 1. to the dwarf and bright-dwarf sequences common to the Hyades and Pleiades, the colorluminosit array for the Pleiades shows two additional sequences, designated here as the "bluedwarf" and "bright blue-dwarf" sequences. Two stars in the Hyades, which were found to lie off the dwarf sequence, fall on the bright blue-dwarf sequence defined by the Pleiades. Of the near-by stars, Sirius falls on the blue-dwarf sequence. The available spectrophotometric data indicate that the separation between the blue-dwarfs and bright blue-dwarfs also appears in the spectra of the Pleiades stars; the hydrogen absorption in the bright blue-dwarfs is about 80 per cent of that in the blue-dwarfs 2. The Pleiades do not populate the blue end of the dwarf sequence, as defined by the Hyades stars, brighter than M = +2.6, that is to say, above the intersection of the dwarf and blue-dwarf sequences. Ano, the Pleiades do not contain bright-dwarfs with M < +2.8. It has previously been shown that at this point on the bright-dwarf sequence in the Hyades, the stars of luminosity class III (A giants) are separated from those of class IV (F subgiants) by the metallic-line stars. The lack of red giants in the Pleiades has been known for some time, but now it appears that the absence of giants also holds true among the early-type stars as well. 3. Where the bright-dwarf and bright blue-dwarf sequences join, or intersect, tFe dwarf sequence in the Pleiades, metallic-line stars appear to occur in the color4uminosity array of the Hyades. Pleiades stars occurring at these intersections may also be expected to be metallic-line stars. 4. Fitting the dwarf and bright-dwarf sequences of the Pleiades to those in the Hyades results in a modulus for the Pleiades of m - M = 5.70, or a parallax ir = 0'.'0071. 5. With the exception of two stars, one visual and one spectroscopic binary, the maximum deviation in magnitude of stars in areas A, B, and D from the various sequences amounts to 0.10 mag., which would be expected from tbe dispersion in distance due to the depth of the cluster, whose diameter is about 10 parsecs. 6. Appreciable reddening in the Pleiades is evident only in a small area surrounding Merope. A comparison of a highly reddened A0 star, for which A p = , with two unobscured A0 stars, gives a ratio of total to selective absorption, x = 4.7. 7. Analysis of the available estimates of the rotational velocities of the cluster stars indicates tbat, as in the Hyades, the dwarf sequence contains relatively slowly rotating stars. The bright blue-dwarfs in both clusters also have small rotational velocities. The bright-dwarfs in the Hyades and the blue-dwarfs in the Pleiades are mostly in rapid rotation. Publication: The Astrophysical Journal Pub Date: January 1950 DOI: 10.1086/145241 Bibcode: 1950ApJ...111...81E full text sources ADS | data products SIMBAD (12) Related Materials (6) Part 1: 1950ApJ...111...65E Part 3: 1950ApJ...111..414E Part 4: 1950ApJ...112..141E Part 5: 1951ApJ...113..367E Part 6: 1951ApJ...113..663E Part 7: 1951ApJ...114..141E

Occultations of Pleiades stars by the moon

Occultations of Pleiades stars by the moon

Occultations of Pleiades stars by the moon

Occultations of Pleiades stars by the moon