A spectroscopic survey for lambda Bootis stars. II. The observational data
lambda Bootis stars comprise only a small number of all A-type stars andare characterized as nonmagnetic, Population i, late B to early F-typedwarfs which show significant underabundances of metals whereas thelight elements (C, N, O and S) are almost normal abundant compared tothe Sun. In the second paper on a spectroscopic survey for lambda Bootisstars, we present the spectral classifications of all program starsobserved. These stars were selected on the basis of their Strömgrenuvbybeta colors as lambda Bootis candidates. In total, 708 objects insix open clusters, the Orion OB1 association and the Galactic field wereclassified. In addition, 9 serendipity non-candidates in the vicinity ofour program stars as well as 15 Guide Star Catalogue stars were observedresulting in a total of 732 classified stars. The 15 objects from theGuide Star Catalogue are part of a program for the classification ofapparent variable stars from the Fine Guidance Sensors of the HubbleSpace Telescope. A grid of 105 MK standard as well as ``pathological''stars guarantees a precise classification. A comparison of our spectralclassification with the extensive work of Abt & Morrell(\cite{Abt95}) shows no significant differences. The derived types are0.23 +/- 0.09 (rms error per measurement) subclasses later and 0.30 +/-0.08 luminosity classes more luminous than those of Abt & Morrell(\cite{Abt95}) based on a sample of 160 objects in common. The estimatederrors of the means are +/- 0.1 subclasses. The characteristics of oursample are discussed in respect to the distribution on the sky, apparentvisual magnitudes and Strömgren uvbybeta colors. Based onobservations from the Observatoire de Haute-Provence, OsservatorioAstronomico di Padova-Asiago, Observatório do Pico dosDias-LNA/CNPq/MCT, Chews Ridge Observatory (MIRA) and University ofToronto Southern Observatory (Las Campanas).
|
The Pre-Main-Sequence Stars and Initial Mass Function of NGC 2264
UBVRI and Hα CCD photometry has been performed in the southernregion of NGC 2264 around the Cone Nebula. A nearly complete list ofpre-main-sequence (PMS) members in the cluster has been made from thecompilation of Hα emission stars identified in this study plusthose selected in previous investigations, together with stars withX-ray emission. Using the H-R diagram, we tested a set of four PMSevolution models based on the PMS age and age spread estimate for thecluster and the mass-age relationship among individual stars. Theresultant initial mass function (IMF) is in good agreement with thefield star IMF of the solar neighborhood, with an IMF slope Γ=-1.7in the mass range 0.3<=logm<=0.8.
|
Spectral classification of O-M stars on the basis of UBV photometry
A new technique allowing the Q-method to be used surely for both thespectral classification of young O-A0 stars and older spectralsubclasses A1-M5 is described. Characteristics of interstellar lightabsorption dependence on distance in the given direction of the sky isused as a main criterion for excluding possible multiplicity of starspectral estimates at some constant values of QUBV.Information on open cluster membership probabilities is also useful asadditional criterion of the spectral classification. The method wastested on stars up to V=14 mag in directions of young open clusters NGC2244 and NGC 2264. The spectral study based on UBV photometry wasextended to faint stars of NGC 2264 in the V magnitude range 17-22 mag.
|
BVRI photometry of the star-forming region NGC 2264: the initial mass function and star-forming rate
The pre-main sequence (PMS) population in the mass range between ~ 0.2and ~ 3 M_sun in southern part of the star-forming region NGC 2264 hasbeen studied, determining both the Initial Mass Function in the regionas well as the star-formation rates for different mass ranges. Thesample is a composite one, derived through the union of samples obtainedthrough different techniques and each suffering from different biases:previously known PMS stars in the region from the literature,photometrically-selected T Tauri candidates (from our own photometricdata, discussed in detail in the present paper) and X-ray selected PMScandidates (discussed in detail in a companion paper) have been joinedto form a sample which we show to be statistically complete (i.e. freefrom the biases which affect each of the parent samples) down to =~ 0.6M_sun (while being incomplete at lower masses). Individual masses andages have been derived by placing the individual stars on evolutionarytracks, allowing us to derive both the IMF and the star formation rate.The Initial Mass Function thus derived for NGC 2264 shows evidence for abimodal distribution of masses, with a break in the IMF at around 1M_sun. Based on observations with the VATT: the Alice P. LennonTelescope and the Thomas J. Bannan Astrophysics Facility. Table~3 isavailable in electronic form at CDS via ftp 130.79.128.5
|
VBLUW photometry of the very young open cluster NGC 2264
This study presents and discusses VBLUW photometry of 112 stars with Vless than 13 in the area of the very young cluster NGC 2264.Temperatures, gravities, and reddening for stars hotter than 8400 K aredetermined. The reddening and the distance are found to be in goodagreement with the results of other references; to the existing list ofpresumable nonmembers, six stars are tentatively added as possiblenonmembers.
|
Remarks to Lapicz positions of stars in NGC 2264.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990RMxAA..20..113L&db_key=AST
|
Positions of stars in NGC 2264
Positions in the region of NGC 2264, obtained using the Lick CarnegieAstrograph are presented. The methods used to obtain the positions arebriefly discussed.
|
Study of the open cluster NGC 2264
Photoelectric UBV magnitudes and colors have been determined for 138stars in NGC 2264, having a membership probability greater than 50percent on the basis of proper motion studies. The reddening across thecluster is variable. The distance modulus to the cluster is estimated at9.5 + or - 0.2 mag.
|
The distribution of stars and obscuring matter in a Monoceros field
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&AS....7...35K&db_key=AST
|
Membership of the open cluster NGC 2264.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1965AJ.....70..797V&db_key=AST
|
Studies of Extremely Young CLUSTERS.I.NGC 2264.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1956ApJS....2..365W&db_key=AST
|
