- ID:
- ivo://CDS.VizieR/J/AJ/109/173
- Title:
- BVR photometry of NGC 6822
- Short Name:
- J/AJ/109/173
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Our proposed method to study the star-formation histories in nearby irregulars is here applied to NGC 6822. To this purpose we have obtained accurate CCD photometry of three regions in the galaxy, reaching V=23.5 with the required accuracy of {sigma}_BVR_<=0.1mag. Major information on the stellar populations, star-formation rates, and initial mass functions of these regions in the last 1Gyr are derived from the comparison of the observational color-magnitude diagrams and luminosity functions with the corresponding synthetic diagrams and luminosity functions generated by a numerical simulation code based on stellar evolutionary tracks. We find that in the last 1Gyr the star-formation activity has been rather continuous, possibly occurring in long episodes of moderate activity separated by short quiescent periods, and that the initial mass function exponent a is in the vicinity of Salpeter's value, i.e., slightly flatter than in the solar neighborhood. The studied regions of NGC 6822 appear to contain different stellar populations. The preferred star formation regime for region A is a continuous activity coupled with a moderately flat {alpha}. For region C, instead, our best models suggest a discontinuous star formation and a moderately steep {alpha}. NGC 6822 is the last object of our original sample of five nearby irregulars. We can then draw the scenario resulting from this sample: most of the observed fields appear to have experienced a gasping regime of star formation, with average exponent {alpha}=2.35 for the initial mass function. Despite their small sizes, the majority of the sample galaxies contain different stellar populations in different regions.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/132/1593
- Title:
- BVR photometry of NGC 4594 globular clusters
- Short Name:
- J/AJ/132/1593
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A detailed imaging analysis of the globular cluster (GC) system of the Sombrero galaxy (NGC 4594) has been accomplished using a six-image mosaic from the Hubble Space Telescope Advanced Camera for Surveys. The quality of the data is such that contamination by foreground stars and background galaxies is negligible for all but the faintest 5% of the GC luminosity function. This enables the study of an effectively pure sample of 659 GCs until ~2mag fainter than the turnover magnitude, which occurs at M^TOM^_V_=-7.60+/-0.06 for an assumed m-M=29.77. Two GC metallicity subpopulations are easily distinguishable, with the metal-poor subpopulation exhibiting a smaller intrinsic dispersion in color compared to the metal-rich subpopulation.
- ID:
- ivo://CDS.VizieR/J/AJ/133/1599
- Title:
- B'V'R' photometry of S5 0716+714
- Short Name:
- J/AJ/133/1599
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We first introduce a novel photometric system that consists of a Schmidt telescope, an objective prism, a CCD camera, and, in particular, a multipeak interference filter. The multipeak interference filter enables light in multiple passbands to pass through it simultaneously. The light in different passbands is differentially refracted by the objective prism and is focused on the CCD in separate regions, so we have multiple "images" for each object on the CCD frames. This system enables us to monitor blazars exactly simultaneously in multiple wave bands on a single telescope and to accurately trace the color change during the variation. We used this novel system to monitor the BL Lacertae object S5 0716+714 during 2006 January and February and achieved a very high temporal resolution. The object was very bright and very active during this period. Two strong flares were observed, with variation amplitudes of about 0.8 and 0.6mag in the V' band, respectively.
- ID:
- ivo://CDS.VizieR/J/AJ/110/212
- Title:
- BVR photometry of stars in NGC 2366
- Short Name:
- J/AJ/110/212
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The stellar content of the Im galaxy NGC 2366 is discussed on the basis of CCD BVR photometry. The three brightest blue and red stars have been used to estimate its distance, obtaining a value of 2.9pc. The spatial distribution of the young stellar population is discussed in the light of the integrated color indices and the color-magnitude diagrams of different zones of the galaxy. A generalized star formation burst seems to have taken place about 50Myr ago. The youngest stars are preferentially formed in the South-West part of the bar, where the giant H II complex NGC 2363 is located, being younger and bluer. The bar seems to play a role favoring star formation in one of its extremes. Self-propagation however, does not seem to be triggering star formation at large scale. A small region, populated by very young stars has also been found at the East of the galaxy.
- ID:
- ivo://CDS.VizieR/J/AJ/143/108
- Title:
- B'V'R' photometry of the BL Lac object S5 0716+714
- Short Name:
- J/AJ/143/108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of our optical monitoring of the BL Lac object S5 0716+714 over seven nights in 2006 December. The monitoring was carried out simultaneously at three optical wavelengths with a novel photometric system. The object did not show large-amplitude internight variations during this period. Intranight variations were observed on four nights and probably on one more. Strong bluer-when-brighter chromatism was detected on both intranight and internight timescales. The intranight variation amplitude decreases in the wavelength sequence of B', R', and V'. Cross-correlation analyses revealed that the variability at the B' and V' bands leads that at the R' band by about 30 minutes on one night.
- ID:
- ivo://CDS.VizieR/J/A+A/358/819
- Title:
- BVR photometry of tidal dwarf candidates
- Short Name:
- J/A+A/358/819
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The table gives the colors from the optical photometry of all objects marked on the identification charts in the tails of 10 interacting systems, among them several tidal dwarf galaxy candidates.
- ID:
- ivo://CDS.VizieR/J/PASP/121/699
- Title:
- BVR photometry of V343 Ori
- Short Name:
- J/PASP/121/699
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- BVR light curves of V343 Orionis were observed with the 85cm telescope at Xinglong Station of the National Astronomical Observatories of the Chinese Academy of Sciences, in 2007 and 2008. Using the Wilson-Devinney program, the photometric solution of V343 Ori was first deduced from those observations. Photometric results indicated that V343 Ori is an A-subtype W Ursae Majoris binary, whose mass ratio and overcontact degree are q=0.253(+/-0.004) and f=86.9%(+/-2.1%), respectively.
- ID:
- ivo://CDS.VizieR/J/ApJ/750/59
- Title:
- BVR polarimetric observations of {beta} Lyr
- Short Name:
- J/ApJ/750/59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from six years of recalibrated and new spectropolarimetric data taken with the University of Wisconsin's Half-Wave Spectropolarimeter and six years of new data taken with the photoelastic modulating polarimeter at the Flower and Cook Observatory of beta Lyrae. Combining these data with polarimetric data from the literature allows us to characterize the intrinsic BVRI polarized light curves. A repeatable discrepancy of 0.245 days (approximately 6hr) between the secondary minima in the total light curve and the polarization curve in the V band, with similar behavior in the other bands, may represent the first direct evidence for an accretion hot spot on the disk edge.
- ID:
- ivo://CDS.VizieR/J/A+A/591/A92
- Title:
- BVR polarimetry of HD 48099
- Short Name:
- J/A+A/591/A92
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the structure of the O-type binary system HD 48099 by measuring linear polarization that arises due to light scattering process. High-precision polarimetry provides independent estimates of the orbital parameters and gives important information on the properties of the system. Linear polarization measurements of HD 48099 in the B, V and R passbands with the high-precision Dipol-2 polarimeter have been carried out. The data have been obtained with the 60cm KVA (Observatory Roque de los Muchachos, La Palma, Spain) and T60 (Haleakala, Hawaii, USA) remotely controlled telescopes during 31 observing nights.Polarimetry in the optical wavelengths has been complemented by observations in the X-rays with the SWIFT space observatory. Optical polarimetry revealed small intrinsic polarization in HD 48099 with 0.1% peak to peak variation over the orbital period of 3.08d. The variability pattern is typical for binary systems, showing strong second harmonic of the orbital period. We apply our model code for the electron scattering in the circumstellar matter to put constraints on the system geometry. A good model fit is obtained for scattering of light on a cloud produced by the colliding stellar winds. The geometry of the cloud, with a broad distribution of scattering particles away from the orbital plane, helps in constraining the (low) orbital inclination. We derive from the polarization data the inclination i=17{deg}+/-2{deg} and the longitude of the ascending node Omega=82{deg}+/-1{deg} of the binary orbit. The available X-ray data provide additional evidence for the existence of the colliding stellar winds in the system. Another possible source of the polarized light could be scattering from the stellar photospheres. The models with circumstellar envelopes, or matter confined to the orbital plane, do not provide good constraints on the low inclination, better than i<=27{deg}, as is already suggested by the absence of eclipses.
- ID:
- ivo://CDS.VizieR/J/ApJ/752/42
- Title:
- BV time series in Ursa Major II
- Short Name:
- J/ApJ/752/42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a B, V color-magnitude diagram (CMD) of the Milky Way dwarf satellite Ursa Major II (UMa II), spanning the magnitude range from V~15 to V~23.5mag and extending over an 18x18 arcmin^2^ area centered on the Galaxy. Our photometry goes down to about 2 mag below the Galaxy's main-sequence turnoff that we detected at V~21.5 mag. We have discovered a bona fide RR Lyrae variable star in UMa II, which we use to estimate a conservative dereddened distance modulus for the galaxy of (m-M)_0_=17.70+/-0.04+/-0.12mag, where the first error accounts for the uncertainties of the calibrated photometry, and the second reflects our lack of information on the metallicity of the star. The corresponding distance to UMa II is 34.7^+0.6^_-0.7_(^+2.0^_-1.9_)kpc. Our photometry shows evidence of a spread in the Galaxy's subgiant branch, compatible with a spread in metal abundance in the range between Z=0.0001 and Z=0.001. Based on our estimate of the distance, a comparison of the fiducial lines of the Galactic globular clusters M68 and M5 ([Fe/H]=-2.27+/-0.04 dex and -1.33+/-0.02 dex, respectively), with the position on the CMD of spectroscopically confirmed Galaxy members, may suggest the existence of stellar populations of different metal abundance/age in the central region of UMa II.
