Contents
Images
Upload your image
DSS Images Other Images
Related articles
The transmission spectrum of Earth-size transiting planets
A variety of terrestrial planets with different physical parameters andexotic atmospheres might plausibly exist outside our Solar System,waiting to be detected by the next generation of space-explorationmissions. Some of these planets might be transiting their parent star.We present here a detailed study of the atmospheric signatures oftransiting Earth-size exoplanets. We focus on a limited number ofsignificant examples, for which we discuss the detectability of some ofthe possible molecules present in their atmospheres, such as water(H2O), carbon dioxide (CO2), ozone (O3), or molecular oxygen (O2). Tothis purpose, we developed a model to simulate transmission spectra ofEarth-size exoplanets from the ultraviolet (UV) to the near infrared(NIR). According to our calculations, the signatures of planetaryatmospheres represent an absorption of a few parts-per-million (ppm) inthe stellar flux. The atmospheres of a few Earth-like planets can bedetected with a 30-40 m telescope. The detection of the extensiveatmospheres of tens of small satellites of giant exoplanets and hundredsof hypothetical ocean-planets can be achieved with 20-30 m and 10-20 minstruments, respectively, provided all these planets are frequent andthey are efficiently surveyed. We also found that planets around K starsare favored, mainly because these stars are more numerous and smallercompared to G or F stars. While not addressed in this study, limitationsmight come from stellar photometric micro-variability.
| ATLAS Versus NextGen Model Atmospheres: A Combined Analysis of Synthetic Spectral Energy Distributions
We carried out a critical appraisal of the two theoretical models,Kurucz' ATLAS9 and PHOENIX/NextGen, for stellar atmosphere synthesis.Our tests relied on the theoretical fit of spectral energy distributions(SEDs) for a sample of 334 target stars along the whole spectral-typesequence, from the classical optical catalogs of Gunn & Stryker andJacoby et al. The best-fitting physical parameters (Teff,logg) of stars allowed an independent calibration of the temperature andbolometric scale versus empirical classification parameters (i.e.,spectral type and MK luminosity class); in addition, the comparison ofthe synthetic templates from the ATLAS and NextGen grids allowed us toprobe the capability of the models to match spectrophotometricproperties of real stars and assess the impact of the different inputphysics. We can sketch the following main conclusions of our analysis:(1) Fitting accuracy of both theoretical libraries drastically degradesat low Teff at which both ATLAS and NextGen models still failto properly account for the contribution of molecular features in theobserved SED of K-M stars. (2) Compared with empirical calibrations,both ATLAS and NextGen fits tend, on average, to predict slightly warmer(by 4%-8%) Teff for both giant and dwarf stars of fixedspectral type, but ATLAS provides, in general, a sensibly better fit (afactor of 2 lower σ of flux residuals) than NextGen. (3) There isa striking tendency of NextGen to label target stars with an effectivetemperature and surface gravity higher than that of ATLAS. The effect isespecially evident for MK I-III objects for which about one in fourstars is clearly misclassified by NextGen in logg. This is a consequenceof some ``degeneracy'' in the solution space, partly induced by thedifferent input physics and geometry constraints in the computation ofthe integrated emerging flux (ATLAS model atmospheres assume standardplane-parallel layers, while NextGen adopts, for low-gravity stars, aspherical-shell geometry). A different T(τ) vertical structure ofstellar atmosphere seems also required for NextGen synthetic SEDs inorder to better account for limb-darkening effects in cool stars, assupported by the recent observations of the EROS BLG2000-5 microlensingevent.
| Photometric Separation of Stellar Properties Using SDSS Filters
Using synthetic photometry of Kurucz model spectra, we explore thecolors of stars as a function of temperature, metallicity, and surfacegravity with Sloan Digital Sky Survey (SDSS) filters, u'g'r'i'z'. Thesynthetic colors show qualitative agreement with the few publishedobservations in these filters. We find that the locus of synthetic starsis basically two-dimensional for 4500 < T < 8000 K, whichprecludes simultaneous color separation of the three basic stellarcharacteristics we consider. Colors including u' contain the mostinformation about normal stellar properties; measurements in this filterare also important for selecting white dwarfs. We identify two differentsubsets of the locus in which the loci separate by either metallicity orsurface gravity. For 0.5 < g' - r' < 0.8 (corresponding roughly toG stars), the locus separates by metallicity; for photometric error of afew percent, we estimate metallicity to within ~0.5 dex in this range.In the range -0.15 < g' - r' < 0.00 (corresponding roughly to Astars), the locus shows separation by surface gravity. In both cases, weshow that it is advantageous to use more than two colors whendetermining stellar properties by color. Strategic observations in SDSSfilters are required to resolve the source of a ~5% discrepancy betweensynthetic colors of Gunn-Stryker stars, Kurucz models, and externaldeterminations of the metallicities and surface gravities. The syntheticstar colors can be used to investigate the properties of any normal starand to construct analytic expressions for the photometric prediction ofstellar properties in special cases.
| ICCD Speckle Observations of Binary Stars. XVII. Measurements During 1993-1995 From the Mount Wilson 2.5-M Telescope.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1639H&db_key=AST
| Mesures d'etoiles doubles faites a Nice, etoiles doubles nouvelles (24eme serie) decouvertes a Nice.
Table 1 gives 1182 measurements of 682 binaries observed with the 74 and50 cm refractors. Table 2 lists 26 new binaries discovered with the 50cm refractor.
| On an Adopted Energy Distribution in Stellar Spectra - Main-Sequence Stars of the G-Type
Not Available
| Association of supernovae with recent star formation regions in late type galaxies
Results are reported from a statistical study carried out to constrainthe various models for the progenitors of supernovae of types Ia, Ib/c,and II. Star-formation regions in late-type galaxies are traced out by HII regions, imaged through photographic and CCD observations, andpossible supernova association with these regions is based on the ratioof the angular separation of each supernova from its nearest H II regionto the angular extent of the H II region in the direction of thesupernova. The specific problems of supernova classification andpositional uncertainties, as well as the probability of chancesuperposition, are also considered. It is suggested that type Iasupernovae do not arise from massive short-lived stellar populations.Type Ib/c and type II supernovae are very likely to be associated with HII regions and therefore with massive stellar progenitors.
| Binary-star measurements carried out at PIC DU Midi and at Nice
Data on 219 measurements of 103 close binaries observed with the 2mtelescope at Pic du Midi are presented. Also presented are data on 230measurements of 126 binaries observed with the 74 cm refractor of theNice Observatory.
| Stellar spectrophotometric atlas, wavelengths from 3130 to 10800 A
Over the course of the past 10 years, a large body of homogeneousspectrophotometric data on relatively bright stars has been gathered toserve as a library with which to synthesize galaxy spectra in populationstudies. As the data might be generally useful, they are presented inthree tables. One hundred seventy-five (175) stars were selected, mostfrom the Navy photometric catalog. Covered are complete ranges ofspectral type and luminosity class. Normalized spectral energydistributions of these stars in pictorial form are provided along withtables of calculated colors, scan line and continuum indices, and someinformation on the relation of the scan colors to real photometricsystems.
| Mesures d'étoiles doubles faites à Nice
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&AS....6..185C&db_key=AST
| Mesures d'étoiles doubles visuelles
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970A&AS....3...71M&db_key=AST
| Mesures d'étoiles doubles à Meudon (2^éme série)
Not Available
| Mesures d'étoiles doubles faites au réfracteur de 38 cm de l'Observatoire de Nice
Not Available
| Colors, luminosities, and motions of the nearer G-type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1964AJ.....69..570E&db_key=AST
| Mesures d'étoiles doubles faites au réfracteur de 38 cm de l'Observatoire de Nice
Not Available
| Mesures d'étoiles doubles faites au 0,38 m de l'Observatoire de Paris.
Not Available
| Mesures d'étoiles doubles faites à l'Observatoire de Paris
Not Available
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Hercules |
| Right ascension: | 17h06m17.83s |
| Declination: | +26°31'04.4" |
| Apparent magnitude: | 8.687 |
| Distance: | 84.459 parsecs |
| Proper motion RA: | -28.3 |
| Proper motion Dec: | 3.3 |
| B-T magnitude: | 9.442 |
| V-T magnitude: | 8.75 |
Catalogs and designations:
|
