AN EMPIRICAL UBV RI JHK COLOR-TEMPERATURE CALIBRATION FOR STARS

We present a method to determine effective temperatures, angular semi-diameters and bolometric corrections for population I and II FGK type stars based on V and 2MASS IR photometry. Accurate calibration is accomplished by using a sample of solar analogues, whose average temperature is assumed to be equal to the solar effective temperature of 5777 K. By taking into account all possible sources of error we estimate associated uncertainties to better than 1% in effective temperature and in the range 1.0–2.5% in angular semi-diameter for unreddened stars. Comparison of our new temperatures with other determinations extracted from the literature indicates, in general, remarkably good agreement. These results suggest that the effective temperaure scale of FGK stars is currently established with an accuracy better than 0.5%–1%. The application of the method to a sample of 10 999 dwarfs in the Hipparcos catalogue allows us to define temperature and bolometric correction (K band) calibrations as a function of (V − K), [m/H ]a nd logg. Bolometric corrections in the V and K bands as a function of Teff ,[ m/H] and log g are also given. We provide effective temperatures, angular semi-diameters, radii and bolometric corrections in the V and K bands for the 10 999 FGK stars in our sample with the corresponding uncertainties.

The results of broad-band BVRcIcJHKL' photometry of late-type stars are used to define a bolometric correction BCIc as a function of (V-I)c or (R-I)c, where mbol = Ic + BCIc. The bolometric corrections BCH and BCK are also derived, and simple analytic expressions are given for BCIc, BCH, and BCK as functions of color index.

A multi-band photoelectric photometer for observations in the ultraviolet, blue and visible and the infrared bands W (1.06μm), X (1.13 μm, Y (1.63 μm) and Z (2.21 μm) has been constructed and applied to both stellar and planetary observations. The results of photometry obtained for 61 stars are presented. The observations at λ = 1.63 μm are shown to exhibit an excess flux due to a minimum in the H opacity in accordance with the predictions of model atmosphere studies. Bolometric corrections are derived for stars of late spectral type from integration of the observed absolute spectral irradiance curve. A simple photometric method for the measurement of stellar diameters is proposed based upon the absolute irradiance observed at 2.21 μm and the 2.21 μm flux at the surface of the star calculated from model atmospheres. Angular diameters derived by this technique are consistent with interferometric results; and, when combined with the bolometric corrections, effective temperatures are found.

JHK photometry of carbon stars and their effective temperature

view Abstract Citations (71) References (63) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The RR Lyrae Variable Stars in the Globular Cluster M15 Silbermann, N. A. ; Smith, Horace A. Abstract New CCD photometry is presented for RR Lyrae variable stars in the globular cluster M15. This photometry, mainly in V and R, with some additional B and I, is used to construct lightcurves of 44 RR Lyraes and one Cepheid in M15. One new low-amplitude RR Lyrae star was discovered. The observable parameters of the light curves are used, in conjunction with theoretical photometric indices, to obtain effective temperatures and bolometric magnitudes for the RR Lyrae stars. We confirm that the regions occupied by RRab and RRcd variables in M15 have little or no overlap in effective temperature. Photometry for variable and nonvariable horizontal branch stars in Ml5 is used to establish the high and low temperature boundaries of the instability strip. There is evidence that the blue edge of the M15 RR Lyrae instability strip becomes cooler at higher luminosities. Employing Cox's value of the mass of RRd stars, 0.75 Msun, and the pulsation equation, the absolute magnitude of the RR Lyrae stars in M15 is estimated to be <MV>= +0.36±0.12 mag. However, this result depends upon the adopted mass, bolometric correction, and color-temperature relation, which remain significantly uncertain. The implications of the absolute magnitude determination for the ages of the globular clusters are discussed. Publication: The Astronomical Journal Pub Date: August 1995 DOI: 10.1086/117555 Bibcode: 1995AJ....110..704S Keywords: STARS: VARIABLES: RR LYRAE; GLOBULAR CLUSTERS: INDIVIDUAL: M15 full text sources ADS | data products SIMBAD (82) CDS (1) Related Materials (1) Erratum: 1996AJ....111..567S

We present an analysis of the intrinsic colors and temperatures of 5-30 Myr old pre-main sequence (pre-MS) stars using the F0 through M9 type members of nearby, negligibly reddened groups: Eta Cha cluster, TW Hydra Association, Beta Pic Moving Group, and Tucana-Horologium Association. To check the consistency of spectral types from the literature, we estimate new spectral types for 52 nearby pre-MS stars with spectral types F3 through M4 using optical spectra taken with the SMARTS 1.5-m telescope. Combining these new types with published spectral types, and photometry from the literature (Johnson-Cousins BVIc, 2MASS JHKs and WISE W1, W2, W3, and W4), we derive a new empirical spectral type-color sequence for 5-30 Myr old pre-MS stars. Colors for pre-MS stars match dwarf colors for some spectral types and colors, but for other spectral types and colors, deviations can exceed 0.3 mag. We estimate effective temperatures (Teff) and bolometric corrections (BCs) for our pre-MS star sample through comparing their photometry to synthetic photometry generated using the BT-Settl grid of model atmosphere spectra. We derive a new Teff and BC scale for pre-MS stars, which should be a more appropriate match for T Tauri stars than often-adopted dwarf star scales. While our new Teff scale for pre-MS stars is within ~100 K of dwarfs at a given spectral type for stars <G5, for G5 through K6, the pre-MS stars are ~250 K cooler than their main sequence counterparts. Lastly, we present (1) a modern Teff, optical/IR color, and bolometric correction sequence for O9V-M9V MS stars based on an extensive literature survey, (2) a revised Q-method relation for dereddening UBV photometry of OB-type stars, and (3) introduce two candidate spectral standard stars as representatives of spectral types K8V and K9V.

Context. Precise and accurate determinations of effective temperature and surface gravity are mandatory to derive reliable chemical abundances and fundamental parameters like distances, masses, radii, luminosities of OB stars. Aims. Atmospheric parameters recently determined at high precision with several independent spectroscopic indicators in NLTE are employed to calibrate photometric relationships. Methods. Temperatures and gravities of 30 calibrators are compared to reddening-independent quantities of the Johnson and Stroemgren photometric systems. We also examine the spectral and luminosity classification of the star sample and compute bolometric corrections. Results. Calibrations of temperatures and gravities are proposed for various photometric indices and spectral types. Effective temperatures can be determined at a precision of ~400 K for luminosity classes III/IV and ~800 K for luminosity class V. Surface gravities can reach internal uncertainties as low as ~0.08 dex when using our calibration to the Johnson Q-parameter. Similar precision is achieved for gravities derived from the beta-index and the precision is lower for both atmospheric parameters when using the Stroemgren indices c1 and [u-b]. Our uncertainties are smaller than typical differences among other methods in the literature, reaching values up to ~2000 K for temperature and ~0.25 dex for gravity, and in extreme cases, ~6000 K and ~0.4 dex, respectively. A parameter calibration for sub-spectral types is also proposed. We present a new bolometric correction relation to temperature based on our empirical data. Conclusions. The photometric calibrations presented here are useful tools to estimate effective temperatures and surface gravities of non-supergiant OB stars in a fast manner. We recommend to use these calibrations as a first step, with subsequent refinements based on spectroscopy (abridged).

We present new grids of colors and bolometric corrections for F-K stars having 4000 K ≤ Teff ≤ 6500 K, 0.0 ≤ log g ≤ 4.5, and -3.0 ≤ [Fe/H] ≤ 0.0. A companion paper extends these calculations into the M giant regime (3000 K ≤ Teff ≤ 4000 K). Colors are tabulated for Johnson U-V and B-V, Cousins V-R and V-I, Johnson-Glass V-K, J-K, and H-K, and CIT/CTIO V-K, J-K, H-K, and CO. We have developed these color-temperature relations by convolving synthetic spectra with the best-determined, photometric filter transmission profiles. The synthetic spectra have been computed with the SSG spectral synthesis code using MARCS stellar atmosphere models as input. Both of these codes have been improved substantially, especially at low temperatures, through the incorporation of new opacity data. The resulting synthetic colors have been put onto the observational systems by applying color calibrations derived from models and photometry of field stars that have effective temperatures determined by the infrared flux method. These color calibrations have zero points that change most of the original synthetic colors by less than 0.02 mag, and the corresponding slopes generally alter the colors by less than 5%. The adopted temperature scale, that of Bell & Gustafsson, is confirmed by the extraordinary agreement between the predicted and observed angular diameters of these field stars, indicating that the differences between the synthetic colors and the photometry of the field stars are not due to errors in the effective temperatures adopted for these stars. Thus, we have derived empirical color-temperature relations from the field star photometry, which we use as one test of our calibrated, theoretical, solar-metallicity color-temperature relations. Except for the coolest dwarfs (Teff < 5000 K), our calibrated model colors are found to match these relations, as well as the empirical relations of others, quite well, and our calibrated, 4 Gyr, solar-metallicity isochrone also provides a good match to color-magnitude diagrams of M67. We regard this as evidence that our calibrated colors can be applied to many astrophysical problems, including modeling the integrated light of galaxies. Because there are indications that the dwarfs cooler than 5000 K may require different optical color calibrations than the other stars, we present additional colors for our coolest dwarf models that account for this possibility.

A new program of accurate photoelectric photometry for the brightest stars is getting underway, using the excellent small telescopes and talents of amateur astronomers.

A new program of accurate photoelectric photometry for the brightest stars is getting underway, using the excellent small telescopes and talents of amateur astronomers.

In this paper we present new and accurate photometry for stars in the Galactic globular cluster NGC 6362. The color-magnitude diagram discloses two peculiarities in the distribution of stars: (1) a slightly tilted horizontal branch (HB) (Δ = 0.1 mag) and (2) a clump of stars near the red edge of the HB. We perform a detailed comparison with theoretical stellar models in both the HB and red giant branch (RGB) phases. It appears that in the moderately metal rich NGC 6362 the tilted HB can be explained as a natural product of canonical evolutionary theories, being a consequence of the minimum in the bolometric correction near 7500 K. We also investigate the effect of decreasing the efficiency of convective transport in stars climbing the RGB. Adopting Z = 0.002 and Y = 0.23, and performing a global fitting with the theoretical isochrones and zero-age HB, an age of 12 ± 1 Gyr is found, together with (m - M)V = 14.68 and E(B-V) = 0.08.

view Abstract Citations (77) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Empirical Mass-Luminosity Relation. Kuiper, G. P. Abstract After a brief historical introduction the problem is subdivided into two main parts. The first, on the temperature scale and bolometric corrections, is treated in the preceding article. The second problem, the derivation of the emphical mass-luminosity refation, is treated in three sections in this article: (i) the visual bhiaries, (2) some selected spectroscopic binaries, and (~) Trumpler's massive stars in clusters. An at- tempt has been made to obtain the most accurate observational data for all quantities entering into the discussion, including magnitudes and spectral types. Tables i and 7 giive the visual binaries used at present. Table 5 shows the derived quantities for the stars of Table i, and Table 6 shows the quantities of theoretical interest for the stars of Table 5 for which the accuracy is sufficiently great. Visual binaries in the same class as those of Table i, but for which the data are still incomplete, are collected i~ Table 8. The problem of the spectroscopic binaries is only partly treated in this paper. Only some representative objects are discussed; they are found in Table 12. Theoretical values of the ellipticity and reflection constants are used in the discussion of the ob- servations. Trumpler's massive stars are discussed in Table 13. In all three sections the results of the preceding article have been used. The data are shown graphically in Figures i and 2 Publication: The Astrophysical Journal Pub Date: November 1938 DOI: 10.1086/143999 Bibcode: 1938ApJ....88..472K full text sources ADS |

We present 56Ni mass estimates for 110 normal Type II supernovae (SNe II), computed here from their luminosity in the radioactive tail. This sample consists of SNe from the literature, with at least three photometric measurements in a single optical band within 95–320 d since explosion. To convert apparent magnitudes to bolometric ones, we compute bolometric corrections (BCs) using 15 SNe in our sample having optical and near-IR photometry, along with three sets of SN II atmosphere models to account for the unobserved flux. We find that the I- and i-bands are best suited to estimate luminosities through the BC technique. The 56Ni mass distribution of our SN sample has a minimum and maximum of 0.005 and 0.177 M⊙, respectively, and a selection-bias-corrected average of 0.037 ± 0.005 M⊙. Using the latter value together with iron isotope ratios of two sets of core-collapse (CC) nucleosynthesis models, we calculate a mean iron yield of 0.040 ± 0.005 M⊙ for normal SNe II. Combining this result with recent mean 56Ni mass measurements for other CC SN subtypes, we estimate a mean iron yield &amp;lt;0.068 M⊙ for CC SNe, where the contribution of normal SNe II is &amp;gt;36 per cent. We also find that the empirical relation between 56Ni mass and steepness parameter (S) is poorly suited to measure the 56Ni mass of normal SNe II. Instead, we present a correlation between 56Ni mass, S, and absolute magnitude at 50 d since explosion. The latter allows to measure 56Ni masses of normal SNe II with a precision around 30 per cent.

A new calibration of the (B — V)0, (V — R)0 and (V — I)0 colours in the Kron-Cousins system for F to M supergiants and of the (V — K)0 colours in the SAAO system of K to M supergiants in the LMC as measures of effective temperature and bolometric correction is given. For F to G supergiants the theoretical Teff-intrinsic colour-relations given by Lejeune et al. (1997) on the basis of their own model atmospheres agree mostly well with our observations. For K to M supergiants, however, their intrinsic colours are too red in most cases. The relations given by Bessell et al. (1998) based on the model atmospheres of Plez (1997) fit the observations better, but their synthetic colours are often also too red. The calibration of the bolometric correction is not reproduced well by any of the models. The HRD of the stars shows two distinct groups, one with log Teff above 3.80 and one with log Teff between 3.53 and 3.62. The upper luminosity and therefore the mass limit depends significantly on effective temperature. The F to G stars have Mbol up to -9.8 mag (corresponding to 45 M⊙), while the K to M stars do not exceed -9.0 mag (corresponding to 31 M⊙). Neither the Geneva nor the Padova models can fit the positions of the most luminous and the coolest supergiants. The discrepancy between theory and observation increases both with increasing mass loss rate and overshooting. Best agreement with the observations is reached by assuming mass loss rates of 2/3 of the de Jager et al. (1988) mass loss rates. As shown both by the luminosity and initial mass function, very luminous (i.e. massive) stars are overproportionally rare. With -3.73 ± 0.20 the slope of the initial mass function is very steep in the considered range of 16-35 M⊙, but confirms the results obtained by Massey et al. (1995) from an extensive study of the field OB stars both in the Magellanic Clouds and the Galaxy.

A new calibration of the (B — V)0, (V — R)0 and (V — I)0 colours in the Kron-Cousins system for F to M supergiants and of the (V — K)0 colours in the SAAO system of K to M supergiants in the LMC as measures of effective temperature and bolometric correction is given. For F to G supergiants the theoretical Teff-intrinsic colour-relations given by Lejeune et al. (1997) on the basis of their own model atmospheres agree mostly well with our observations. For K to M supergiants, however, their intrinsic colours are too red in most cases. The relations given by Bessell et al. (1998) based on the model atmospheres of Plez (1997) fit the observations better, but their synthetic colours are often also too red. The calibration of the bolometric correction is not reproduced well by any of the models. The HRD of the stars shows two distinct groups, one with log Teff above 3.80 and one with log Teff between 3.53 and 3.62. The upper luminosity and therefore the mass limit depends significantly on effective temperature. The F to G stars have Mbol up to -9.8 mag (corresponding to 45 M⊙), while the K to M stars do not exceed -9.0 mag (corresponding to 31 M⊙). Neither the Geneva nor the Padova models can fit the positions of the most luminous and the coolest supergiants. The discrepancy between theory and observation increases both with increasing mass loss rate and overshooting. Best agreement with the observations is reached by assuming mass loss rates of 2/3 of the de Jager et al. (1988) mass loss rates. As shown both by the luminosity and initial mass function, very luminous (i.e. massive) stars are overproportionally rare. With -3.73 ± 0.20 the slope of the initial mass function is very steep in the considered range of 16-35 M⊙, but confirms the results obtained by Massey et al. (1995) from an extensive study of the field OB stars both in the Magellanic Clouds and the Galaxy.