Spectral types fromuvbyβ photometry

New diagrams are presented for the assimilation of MK spectral types withuvby photometry, based upon reddening-free parameters calculated using revised reddening ratios and recently published values of meanuvby colours and indices for a selection of MK spectral types.     

Combined UBV and uvby photometry of open clusters. I. NGC 1502

For at all 24 stars in the field of the heavity reddened open cluster NGC 1502 we obtained UBV and uvby photometry. 19 of these stars we classified definitely as members. From the photometric results we derived 1·1 × 10⁷ years as the cluster age, 960 pc as its distance, and <E(B—V)> = 0·78 mag as mean reddening of the cluster. From the reddening of the foreground stars we evaluated that the intracluster reddening has to be smaller than 0·2 mag. The value of the colour excess ratio E(b—y)/E(B—V) = 0·770 leads us to the conclusion that in the spectra of the cluster stars a very broadband structure (VBS) with a central depth of about 0·04 mag is present.     

Effects of rotation on colours and line indices of stars

We have analysed the broad-bandUBV colours and the intermediate banduvby colours of Persei, Pleiades, and the Scorpio-Centaurus association for rotation effects. An attempt was made to see if we can discriminate normal single stars from that of binary and peculiar stars after taking the observed rotation effects into account. It is found that the spread in the observed colours does not allow in general such a discrimination except that the objects with large reddening are double-lined binaries, peculiar stars or emission-lined objects. The few normal stars in these three clusters with such large reddening are listed as they are likely to belong to one of the above classes.On leave of absence from Assumption College, Changanacherry, Kerala.     

A method of colour excess determination for classical cepheids

By use of the reddening free [m ₁], [c ₁], and indices data inuvby photometric system for three classical cepheids whose reddening values had been determined with the aid of photometry of field stars, three intrinsic relations of [m ₁]–(b–y), [c ₁]–(b–y), and –(b–y) have been established. It was shown that these three relations can be used to determine the colour excesses for other classical cepheids.     

Auvbyβ survey for Ca II emission stars

During the last two years auvby photometric survey of 85 Ca II emission stars from the Mount Wilson program on stellar activity has been carried out at the Calar Alto Observatory (Almeria, Spain). We present preliminary results for theuvby and calibrations. Some stars displaying anomalousc ₁ andm ₁ indices, with photometric or spectroscopic data from previous studies, are reported. A reddening study for the complete sample is given.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

uvby photometry of open clusters

Für insgesamt 40 Stern im Gebiet des verfärbten offenen Haufens NGC 6871 erhieken wir eine uvby Photometric. 21 dieser Sterne klassifizierten definitely as members. From the photometric results we derived 1.2 × 10⁷ years as the cluster age, 2440 pc as its distance, and E(b - y)) = 0.348 mag as mean reddening of the cluster. From the scatter around this mean colour excess and the deviation of a subgroup of stars by more than twice the standard deviation a varible intracluster reddening in order of 0.1 mag is indicated. The value of the colour excess ratio E(b - y)/E(B - V) = 0.705 for the cluster stars leads us to the conclusion that the very broadband structure (VBS) in the spectra of the cluster stars must be very weak. Für insgesamt 40 Stern im Gebiet des verfärbten offenen Haufens NGC 6871 erhielten wir eine uvby Photometrie. 21 dieser Sterne klassifizieren wir definitiv als Haufenmitglieder. Aus den photometrischen Ergebnissen leiteten wir ein Haufenalter von 1.2 × 10⁷ Jahren, eine Entfernung von 2440 pc und eine Verfärbung E (b - y) = 0.348 mag ab. Aus der Streuung um diesen mittleren Farbexzeß und der Tatsache, daß eine Gruppe von Sternen um mehr als die doppelte Standardabweichung von diesem Wert differiert, läßt sich eine Verfärbung innerhalb des Haufens in der Größenordnung von 0.1 mag vermuten. Aus der Größe des Farbexzeßverhältnisses E(b - y )/E(B - V) = 0.705 schließen wir, daß die Breitbandstruktur (VBS) in den Spektren der Haufensterne nur sehr schwach ausgeprägt sein kann.     

Numerical simulation of colour equations for the uvby system

The results of numerical simulation of colour equations of uvby photometry for filter-defined bandpasses are presented. It is shown that linear transformation equations to the standard system are valid for instrumental systems deviating by no more than 2.5 nm in peak transmission wavelengths. The comparison with the results of observations is satisfying. Im Ergebnis einer numerischen Farbgleichungssimulation im uvby-System wird nachgewiesen, daß für Instrumentensysteme mit Abweichungen der Wellenlängen maximaler Transmission bis zu 2.5 nm gegenüber den Standardwerten eine lineare Transformation möglich ist. Der Vergleich mit Beobachtungsresultaten zeigt eine gute Übereinstimmung.     

Photographicuvby photometry of the open cluster M52

Photographicuvby photometry of 15 stars in the open cluster M52 (NGC 7654) has been obtained. The distance modulusV _o–M _v=11.3±0.1 and mean cluster reddeningE(B–V)=0.57 are determined. Some basic physical characteristics of 30 stars with observeduvby values are obtained as well as a numerical estimation of the open cluster age 9.6×10⁷ yr is made.     

Reddening map around α Orionis

uvby photometry has been done for early-type stars in the surroundings of the shell star Ori. The reddening maps show the presence of irregularly distributed absorbing material.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Influence of Interstellar and Atmospheric Extinction on Light Curves of Eclipsing Binaries

Interstellar and atmospheric extinctions redden the observational photometric data and they should be handled rigorously. This paper simulates the effect of reddening for the modest case of two main sequence T ₁ = 6500 K and T ₂ = 5500 K components of a detached eclipsing binary system. It is shown that simply subtracting a constant from measured magnitudes (the approach often used in the field of eclipsing binaries) to account for reddening should be avoided. Simplified treatment of the reddening introduces systematics that reaches ∼0.01 mag for the simulated case, but can be as high as ∼0.2 mag for, e.g., B8 V-K4 III systems. With rigorous treatment, it is possible to uniquely determine the colour excess value E(B−V) from multi-colour photometric light curves of eclipsing binaries.     

A method for the simultaneous estimation of the fundamental atmospheric parameters using the photometric indices in the BVRI and JHK color systems

This is the second paper in a series reporting a new method developed to estimate the fundamental atmospheric parameters of effective temperature, surface gravity, and metallicity simultaneously. In the first paper three parameters were estimated using only photometric indices in the uvby color system. Whereas, in this paper, we use BVRI and JHK color systems. Using the model atmosphere grids, all three parameter values were estimated with respect to both [(B–V):(V–R)] and [(B–V):(R–I)], as well as [(V–K):(H–K)] and [(J–K):(H–K)] pair indices. It was confirmed that (B–V) and (V–K) indices are good temperature indicators, but all color indices for the BVRI and JHK systems are very poor indicators of metallicity and surface gravity. This new method was applied to a number of field dwarfs and giants, and the results were compared with those from the uvby color system. We found that the JHK color system can compete with the uvby system only in the estimation of temperature.     

Stellar luminosities and radii fromuvbyβ photometry

A linear relation is found to exist between the Barnes-Evans visual surface brightness parameterF _V and the (b-y)₀ colour index ofuvby photometry for spectral types later than G0. Using this relation, and a previously determined relation for spectral types B0-G0, tables of intrinsic colours and indices, absolute magnitude and stellar radius are given for the ZAMS and luminosity classes Ia-V over a wide range of spectral types. Comparison of absolute magnitudes and radii calculated fromuvby photometry with values obtained using the visual magnitude, parallax and angular diameter indicates thatuvby photometry can be used to determineM _V to ±0 ^m .2 and log(R/R ) to ±0.05.     

3D interstellar extinction map within the nearest kiloparsec

The product of the previously constructed 3D maps of stellar reddening (Gontcharov 2010) and Rv variations (Gontcharov 2012) has allowed us to produce a 3D interstellar extinction map within the nearest kiloparsec from the Sun with a spatial resolution of 50 pc and an accuracy of {ie87-1}. Thismap is compared with the 2D reddening map by Schlegel et al. (1998), the 3D extinction map at high latitudes by Jones et al. (2011), and the analytical extinctionmodels by Arenou et al. (1992) and Gontcharov (2009). In all cases, we have found good agreement and show that there are no systematic errors in the new map everywhere except the direction toward the Galactic center. We have found that the map by Schlegel et al. (1998) reaches saturation near the Galactic equator at E(B - V) > 0.8, has a zero-point error and systematic errors gradually increasing with reddening, and among the analytical models those that take into account the extinction in the Gould Belt are more accurate. Our extinction map shows that it is determined by reddening variations at low latitudes and Rv variations at high ones. This naturally explains the contradictory data on the correlation or anticorrelation between reddening and Rv available in the literature. There is a correlation in a thin layer near the Galactic equator, because both reddening and Rv here increase toward the Galactic center. There is an anticorrelation outside this layer, because higher values of Rv correspond to lower reddening at high and middle latitudes. Systematic differences in sizes and other properties of the dust grains in different parts of the Galaxy manifest themselves in this way. The largest structures within the nearest kiloparsec, including the Local Bubble, the Gould Belt, the Great Tunnel, the Scorpius, Perseus, Orion, and other complexes, have manifested themselves in the constructed map.     

Photographic UVB photometry of the globular clusters M 15 and NGC 6712

Photographic intermediate banduvb observations of RGB and some AGB stars in 7 × 7 arcmin fields centered on the globular clusters M 15 and NGC 6712 are obtained. The photometric data is not fully reduced to the standard system but it is converted in an unique instrumental system. The photometry confirms the existence of the gaps in the giant branch of M 15. For NGC 6712 the Stromgren colors show a bimodal distribution and point at a bimodal carbon abundance for the bright giants from the central part. The possibilities of theuvby system for a classification of RGB and AGB stars are briefly discussed.     

Four-color photometry of the Galilean satellites

Photometry obtained in 1973 on the uvby system yields high-precision rotational light curves for Io, Europa, and Ganymede at a mean phase angle of ～6°. By combining our observations with photometry obtained by others over a broader range of phase angle, we alsi derive improved values for the phase coefficients and opposition surges of the four Galilean satellites. The values of V(1, 0) obtained by linear extrapolation to zero phase are accurate to ±0.03 magnitudes. We also derive the colors of the sun of the uvby system and use these to obtain albedos of the satellites in four colors.     

Saao standards for optical photometry

A review is given of the development of systems of photometric standard stars at the South African Astronomical Observatory. A brief historical perspective indicates how the Harvard E-regions were chosen as standard sequences and developed into a very precise Southern hemisphere system for UBV(RI) _c photometry. Subsequent additions of Strömgrenuvby - H and DDO photometry to samples of E-region stars and UBV(RI) _c extensions to the F-regions and the Magellanic Clouds are also described. Current programmes to extend and improve these standard stars are briefly discussed, as well as the long-standing problem of linking the Northern and Southern systems.     

Multicolour photoelectric photometry of the open cluster NGC 752

In the open cluster NGC 752, 89 stars are observed in the Vilnius seven-colour photometric system, including probable members fainter than observed hitherto. Spectral classification of observed stars are made and individual reddening values are determined. The mean reddening of the cluster stars is equivalentE(B - V) = 0 _. ^m 025. By fitting on colour index-magnitude diagrams the cluster Main Sequence with the Hyades one the distance modulus (m - M)₀ = 8 _. ^m 15 ± 0 _. ^m 15 is found. For 11 red giant members of the cluster absolute magnitudes are derived and compared with ones of the standard calibration. It is obtained that the cluster giants are in mean 0 _. ^m 6 fainter than giants of corresponding spectral class in the solar vicinity.     

The distribution of interstellar extinction near the sun

Photometric data inuvbyß system from 3713 stars is used to map the distribution of colour excesses up to 500 parsec from the Sun, producing diagrams for a series of layers aligned with the galactic plane. Individual clouds are detected, with a mean diameter of 6 parsecs, while cloud complexes have a mean diameter of 100 pc. From the maps it seems that the interstellar medium near the Sun presents regions of non-negligible extinction, while the Sun itself is enbedded in a diffuse cloud, or slightly off its border. The large scatter in the distribution ofE(b-) is confirmed, with a mean extinction ofA _v=0 _. ^m 38 up to 500 pc.     

A photometric catalogue of visual and multiple stellar systems

Summary The catalogue gives the parameters of theUBV, uvby, and Geneva photometries for more than 200 stars. It gives also the first statistics with respect to the different caracteristics of visual systems: separation, difference of the magnitude of components,... etc. For 11713 components of stellar systems the catalogue, in its actual form, gives the parameters of theUBV, uvbyβ and Geneva photometric systems. A concise statistics presents the distribution of the stars in the different photometric systems and the relations between the difference in the magnitudes and separation of the components. CNRS UA 040389.     

Interstellar reddening in the direction of the globular cluster M71

Interstellar reddening as a function of distance in the direction of the globular cluster M71 is determined by two-dimensional quantification of 96 foreground stars observed in the Vilnius photometric system. In concentric areas with the radii 30 and 10 centered on the cluster the reddening shows the same variations ranging fromE _B-V=0.12 to 0.32. The cluster stars are likely to have variable extinction too, at least in the outer regions of the cluster.