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The chromospheric emission of solar-type stars in the young open clusters IC 2391 and IC 2602
In this paper we present chromospheric emission levels of the solar-typestars in the young open clusters IC 2391 and IC 2602. High-resolutionspectroscopic data were obtained for over 50 F, G and K stars from theseclusters over several observing campaigns using the University CollegeLondon Echelle Spectrograph on the 3.9-m Anglo-Australian Telescope.Unlike older clusters, the majority (28/52) of the solar-type stars inthe two clusters are rapid rotators (vsini > 20kms-1) withfive of the stars being classified as ultra-rapid rotators (vsini >100 km s-1). The emission levels in the calcium infraredtriplet lines were then used as a measure of the chromospheric activityof the stars. When plotted against the Rossby number (NR),the star's chromospheric emission levels show a plateau in the emissionfor log(NR) <~ -1.1 indicating chromospheric saturationsimilar to the coronal saturation seen in previously observed X-rayemission from the same stars. However, unlike the coronal emission, thechromospheric emission of the stars shows little evidence of a reductionin emission (i.e. supersaturation) for the ultra-rapid rotators in theclusters. Thus we believe that coronal supersaturation is not the resultof an overall decrease in magnetic dynamo efficiency for ultra-rapidrotators.
| Catalogues of radial and rotational velocities of 1253 F-K dwarfs in 13 nearby open clusters
Context: We conducted a long-term monitoring of solar-type dwarfs in 13nearby open clusters, d < 500 pc, over 19 years, but most individualradial velocities were never published, apart from a small number ofspectroscopic binaries. Aims: Our program was designed to studymembership and duplicity, and to search for new cluster members. Methods: We obtained 6070 radial velocities during 19 years ofobservations at the Haute-Provence Observatory (France) and 1130 during13 years at ESO La Silla (Chile) for 1253 stars in the field of 13 openclusters. The zeropoint of the CORAVEL radial velocity system wasimproved and the new values supersede those published previously. Results: The membership and binarity of solar-type stars in NGC 1976(Orion), IC 2602, NGC 7092, and NGC 2682 are briefly discussed. For theentire sample, we confirmed the membership of 894 stars and discovered150 new spectroscopic binaries among them. Added to those already knownin the Hyades and Coma Berenices, the number of member spectroscopicbinaries is 188. The overall binary frequency is 30% (188/618) for starswith at least 2 measurements. Since no spectroscopic binaries were foundamong its 26 members, IC 2602 may however represent an exception. Neworbital elements were computed with the updated values of the radialvelocities for 66 systems, representing 55 members and 11 non-members.Conclusions: This paper is the final report from our team ofCORAVEL radial velocities of solar-type dwarfs in nearby open clusters.All CORAVEL observations for dwarfs and red giants in open clusters arenow available in electronic form.Based on observations collected at the Haute-Provence Observatory(France) and with the Danish 1.54-m at the European SouthernObservatory, La Silla, Chile. This reaserch has made use of the WEBDAdatabase, operated at the Institute for Astronomy of the University ofVienna, and of the SIMBAD database, operated at CDS, Strasbourg, FranceThis publication makes use of data products from the Two Micron All SkySurvey, which is a joint project of the University of Massachusetts andthe Infrared Processing and Analysis Center/California Institute ofTechnology, funded by the National Aeronautics and Space Administrationand the National Science Foundation. Full Tables 8, 10, and 11 are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/498/949
| Rotational Velocities and Chromospheric/Coronal Activity of Low-Mass Stars in the Young Open Clusters IC 2391 and IC 2602
We have obtained high-resolution, moderate signal-to-noise ratio spectrafor approximately 80 candidate low-mass members of the nearby, veryyoung open clusters IC 2391 and IC 2602. Most of the stars observed areconfirmed as cluster members based on a combination of photometric andspectroscopic criteria. We provide radial velocities, rotationalvelocities, and H alpha equivalent widths for these stars. Fromcomparison to theoretical pre--main-sequence (PMS) evolutionaryisochrones from D'Antona and Mazzitelli, we derive an estimated age ofthe two clusters of ~25 Myr. By contrast, the usually quoted uppermain-sequence turnoff age for the clusters is ~35 Myr. We do not believethat this provides evidence for noncoeval star formation within theseclusters, but rather that the best age estimate for them given theuncertainties is ~30 +/- 5 Myr. In principle, the scatter of stars aboutthe PMS isochrone provides a measure of the age spread among thelow-mass stars in these clusters; however, with the data presentlyavailable, we are able to derive only a relatively uninteresting upperlimit for an age spread of order 20 Myr. We compare the rotationalvelocity distribution for IC 2391/2602 to that observed for thePleiades. For the G dwarfs in the IC clusters, we resolve rotation inall but one of the probable cluster members, and thus except forinclination effects, our data provide the complete distribution ofrotational velocities for solar mass stars on their arrival on the ZAMS.The projected rotational velocities (v sin i) of the G dwarfs in the twoIC clusters span the range from ~8 to ~200 km s-1. Comparison of thedistribution of rotational velocities for the G dwarfs of the Pleiadesand the IC clusters indicates that both the slow and the rapid rotatorslose of order half their angular momentum during the first ~35 Myr onthe main sequence if they rotate as solid bodies. The low-mass stars inthese two clusters exhibit a similar correlation between rotation andcoronal activity as is found in several other young open clusters. Thatis, there is a large spread in coronal activity for stars with v sin i< 25 km s-1, where we assume there is an intrinsic link betweenincreasing rotation and increasing activity superimposed upon which area variety of observational and physical mechanisms that act to smear outthis relation; above v sin i ~ 25 km s-1, all of the low-mass stars havelog (LX/Lbol) ~ -3.0, the canonical "saturation" limit. Our measurementsof the H alpha equivalent widths are consistent with a similarrelationship holding for chromospheric activity. One and possibly two ofour spectra for M dwarf members of the IC clusters show broad wings forthe H alpha profile, which we attribute to a flare event or tomicroflares. Since spectra of a small sample of late-type M dwarfs inthe Pleiades also showed similarly broad H alpha wings, this suggeststhat flare frequencies for very young M dwarfs may be quite high.
| An X-ray study of the young open cluster IC 2602.
We present the results of ROSAT PSPC observations of the 30Myr old IC2602 cluster; for the X-ray detected objects the results of a CCDphotometric survey are also given. In X-rays, we detect a total of 110objects within a 11deg^2^ area, above a threshold of typically3-5x10^28^erg/sec. 68 of the detected objects have been identified withat least one optical counterpart; 44 of these are new optical candidatesfor cluster membership provided by our CCD photometry. Stars of allspectral types have been detected, from the very early- types to thelate-M dwarfs. Soft X-ray luminosities range between about 10^29^erg/secto a few 10^30^erg/sec, with the maximum and average L_X_ decreasingwith spectral type for B-V larger than ~0.8. Many of the stars redderthan B-V~0.8 show a L_X_/L_bol_ ratio at about the saturation level of10^-3^. We construct X-ray luminosity distribution functions for objectsin different color ranges and we compare them with those for thePleiades. F, G, and early-K type candidates in IC 2602 appear to be moreX-ray luminous than in the Pleiades, while no significant difference isseen among late-K and M dwarfs. Under the assumption that our IC 2602sample is not severely affected by incompleteness, we argue that theabove finding is related to the distribution of rotational velocities inthe two clusters, with most of the late-type stars being fast rotatorsin both clusters, while, due to different spin-down timescales, theearlier type stars in IC 2602 are likely to rotate more rapidly thantheir counterparts in the Pleiades.
| A study of the galactic cluster IC 2602. I. A photoelectric and spectroscopic investigation
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1961MNRAS.123..245W&db_key=AST
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