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BV Photometry for the ~2.5 Gyr Open Cluster NGC 6819: More Evidence for Convective Core Overshooting on the Main Sequence
New BV photometry is presented for the populous, intermediate-age opencluster NGC 6819. From ~4 mag below the turnoff to ~2 mag above the redgiant clump, the cluster's color-magnitude diagram is well defined. Ofparticular note is the fact that the bright end of the main-sequencedistribution exhibits a pronounced curvature to the red. This morphologycan be matched by theoretical stellar models only if a significantamount of convective core overshooting is assumed. Indeed, canonical,nonovershooting calculations fail by a wide margin to explain theobservations. Comparisons with up-to-date evolutionary tracks,isochrones, and zero-age horizontal-branch loci for [Fe/H] = 0.0 and-0.10 indicate that the [Fe/H] ~ -0.05 cluster has (m - M)_V = 12.35,E(B - V) = 0.16, and an age near 2.4 Gyr. The existence of several clumpstars that appear to be appreciably more massive than the turnoff starsis noted: we suggest that they are the descendants of blue stragglers,given that NGC 6819 has a confirmed blue straggler population.
| UBV(RI)c photometry of equatorial standard stars - A direct comparison between the northern and southern systems
UBV(RI)c photometry of 212 stars from Landolt's list of equatorialstandards is presented. The observations are tied to the system definedby Cousin's E-region standards. A comparison of the present results withLandolt's reveals reasonably good agreement for (V-R)c and (V-I)c, butmarked systematic differences for (B-V) and (U-B). The UBV systems ofCousins and Landolt are evidently not the same and both probably differfrom Johnson's original system.
| A photometric study of the very short period eclipsing binary EH Hydrae
Recent Johnson-Cousins' B,V,Rc,Ic photoelectric observations of the veryshort period W UMa variable, EH Hya, are presented. These observationswere made, using the Yale 1M telescope and the dry-ice-cooled HamamatsuGa-As PMT at Cerro Tololo Inter-Americal Observatory. The light curvesreveal that the eclipses are total, and that the primary eclipse is anoccultation. Thus, the system is of W-type, with the larger componentbeing the cooler. Standard magnitudes were determined, and a reddeningestimate was made. A simultaneous solution of the B,V,R light curves wascomputed using the Wilson-Devinney (1971) synthetic light curve code.The solution indicates that the system consists of two late G-type starsin shallow contact with a fill-out factor of 12 percent. The differencein component temperatures is 336(8) K and the mass ratio is ratherextreme, being 0.314(2). EH Hya is compared to other very short periodbinaries of late G-type, and they are found to comprise a fairlyhomogenous group with regards to mass ratios, degree of thermal contact,and magnetic activity.
| The X-Ray Source HD 197010 is an Eclipsing Binary
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| Photoelectric Photometry of Stars in the Vilnius System in Kapteyn Areas SA:92 SA:108 and SA:112
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| UBVRI photometric standard stars around the celestial equator
It is pointed out that accurate, internally consistent, and readilyaccessible standard star photometric sequences are necessary for thecalibration of the intensity and color data which astronomers obtain atthe telescope. The photometric results provided in connection with thepresent study represent the first part of an effort which is concernedwith the presentation of UBVRI photoelectric photometric standard starsin the magnitude range from 7 to 17 over as broad a range in color aspossible. All of the photometric observations were made with a 31034type photomultiplier used in a pulse counting mode. Some 15 to 25standard stars chosen from Cousins' lists (1973, 1976) in the E-regionswere observed with an 0.4-m telescope each night along with the programstars. UBVRI standard stars were observed periodically throughout thenight. Observations with a 0.9-m telescope were also conducted. TheUBVRI photoelectric observations take into account 223 stars.
| Spectral classifications for Landolt's celestial equatorial standard stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979AJ.....84..783D&db_key=AST
| Equatorial UBVRI photoelectric sequences
From 1335 BVRI observations of 189 stars in selected areas 92-115,Landolt's (1973) network of faint UBV standards has been extended to RI. Of these stars, 173 have four or more observations. The (U-B) valuesof Landolt are adopted, and a well-observed equatorial faint-starnetwork is presented on the Johnson UBVRI photometric system.
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Observation and Astrometry data
| Constellation: | Υδροχόος |
| Right ascension: | 20h42m23.60s |
| Declination: | +00°26'42.1" |
| Apparent magnitude: | 9.085 |
| Proper motion RA: | 5.7 |
| Proper motion Dec: | -18.7 |
| B-T magnitude: | 9.579 |
| V-T magnitude: | 9.126 |
Catalogs and designations:
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