- ID:
- ivo://CDS.VizieR/J/ApJ/713/615
- Title:
- Very metal-poor Cepheid models
- Short Name:
- J/ApJ/713/615
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Classical Cepheids are primary distance indicators playing a fundamental role in the calibration of the extragalactic distance scale. The possible dependence of their characteristic period-luminosity (PL) relation on chemical composition is still debated in the literature, and the behavior of these pulsators at very low metallicity regimes is almost unexplored. In order to derive constraints on the application of the PL relation at low metal abundances, we investigate the properties of the few ultra-low metallicity (Z~0.0004) Cepheids recently discovered in the Blue Compact Dwarf galaxy IZw18. To this purpose, we have computed an updated and extended set of nonlinear convective models for Z=0.0004 and Y=0.24, spanning a wide range of stellar masses, and taking into account the evolutionary constraints for selected luminosity levels. As a result, we are able to predict the topology of the instability strip, the variations of all the relevant quantities along the pulsation cycle, including the morphology of the light curves, the theoretical period-luminosity-color, period-Wesenheit, and PL relations at such a low metallicity.
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- ID:
- ivo://CDS.VizieR/J/other/NewA/48.58
- Title:
- V1044 Her VR differential photometry
- Short Name:
- J/other/NewA/48.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new CCD photometric observations of V1044 Her obtained on May 22, 23 and 24, 2015. From our data, we derived five new light curve minimum times. Combining our new results with previously available CCD light minimum times, we derived an updated ephemeris and discovered that the period of this binary system exhibits an oscillation. The cyclic variation may be caused by the light-time effect via the presence of a third body or magnetic activity cycle. We calculated the corresponding period of the third body to be 14.1+/-1.4 years or magnetic cycle to be 12.2+/-0.7 years. We analyzed our new asymmetric light curves to obtain photometric solutions and starspot parameters using the Wilson and Devinney program. The final results show that V1044 Her is a contact binary system with a degree of contact factor f=3.220(+/-0.002)%.
- ID:
- ivo://CDS.VizieR/J/MNRAS/346/390
- Title:
- VI and CMT1 photometry of NGC 2627
- Short Name:
- J/MNRAS/346/390
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Charge-coupled device (CCD) photometry in the Johnson V, Kron-Cousins I and Washington CMT1 systems is presented in the field of the poorly known open cluster NGC 2627.
- ID:
- ivo://CDS.VizieR/J/MNRAS/349/641
- Title:
- VIc, CT1 magnitudes in Trumpler 5
- Short Name:
- J/MNRAS/349/641
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- CCD observations in the Johnson V, Kron-Cousins I and the Washington system C and T_1_ passbands have been used to generate colour-magnitude diagrams (CMDs) reaching down to V~21.0mag and T_1_~19.0 for Trumpler 5, an old open cluster located towards the Galactic anticentre. Our data analysis confirms the existence of non-uniform extinction over the face of the cluster, the mean E(V-I) and E(C-T_1_) values being 0.80+/-0.05 and 1.17+/-0.15, respectively. Through comparison of the cluster CMDs with theoretical isochrones of the Geneva group, Washington Standard Giant Branches and measures of V and T_1_ indices, we derive the following values for the cluster apparent distance modulus, age, and metallicity: V-M_V_=13.80+/-0.30 (corresponding to a distance from the Sun of 2.4+/-0.5 kpc and 0.04kpc above the Galactic plane), t=5.0+/-0.5Gyr and [Fe/H]=-0.30+/-0.15. We estimate the cluster angular radius to be about 7.7 arcmin (=5.4pc) from star counts carried out within and outside the cluster field.
- ID:
- ivo://CDS.VizieR/J/MNRAS/340/1249
- Title:
- VIc magnitudes in NGC 2194
- Short Name:
- J/MNRAS/340/1249
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present CCD VI_KC_ photometry down to V~21mag in the field of the rich open cluster NGC 2194, which is projected towards the Galactic anticentre direction. We measured V magnitudes and V-I colours for a total of 2515 stars in a field of 13.6x13.6arcmin^2^, supplemented with CCD photometry in the C, M and T_1_ filters of the Washington system and photoelectric CMT_1_T_2_ photometry of 20 red giant candidates, using the 0.9-m telescope at the Cerro Tololo Inter-American Observatory (CTIO), Chile, on 1997 December 23-24.
- ID:
- ivo://CDS.VizieR/J/MNRAS/346/18
- Title:
- VIc photometry in Saurer A, B and C
- Short Name:
- J/MNRAS/346/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report deep (V~24.0) VI CCD photometry of three fields centred in the regions of the old open clusters Saurer A, B and C. In the case of Saurer A, which is considered one of the oldest known open clusters, we also provide a comparison field.
- ID:
- ivo://CDS.VizieR/J/MNRAS/435/3058
- Title:
- VIc photometry of IR-excess stars in NGC6611
- Short Name:
- J/MNRAS/435/3058
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Attention is given to a population of 110 stars in the NGC 6611 cluster of the Eagle nebula that have prominent near-infrared excess and optical colours typical of pre-main-sequence (PMS) stars older than 8Myr. At least half of those for which spectroscopy exists have a H{alpha} emission line profile revealing active accretion. In principle, the V-I colours of all these stars would be consistent with those of young PMS objects (<1Myr) whose radiation is heavily obscured by a circumstellar disc seen at high inclination and in small part scattered towards the observer by the back side of the disc. However, using theoretical models it is shown here that objects of this type can only account for a few percent of this population. In fact, the spatial distribution of these objects, their X-ray luminosities, their optical brightness, their positions in the colour-magnitude diagram and the weak Li absorption lines of the stars studied spectroscopically suggest that most of them are at least eight times older than the ~1Myr-old PMS stars already known in this cluster and could be as old as ~30Myr. This is the largest homogeneous sample to date of Galactic PMS stars considerably older than 8Myr that are still actively accreting from a circumstellar disc and it allows us to set a lower limit of 7 percent to the disc frequency at ~16Myr in NGC 6611. These values imply a characteristic exponential lifetime of ~6Myr for disc dissipation.
- ID:
- ivo://CDS.VizieR/J/MNRAS/377/741
- Title:
- VIc photometry of NGC 2516
- Short Name:
- J/MNRAS/377/741
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the results of an i-band time-series photometric survey of NGC2516 using the Cerro Tololo Inter-American Observatory (CTIO) 4-m Blanco telescope and 8k Mosaic-II detector, achieving better than 1 per cent photometric precision per data point over 15<~i<~19. Candidate cluster members were selected from a V versus V-I colour-magnitude diagram over 16<V<26 (covering masses from 0.7M_{sun}_ down to below the brown dwarf limit), finding 1685 candidates, of which we expect ~1000 to be real cluster members, taking into account contamination from the field (which is most severe at the extremes of our mass range). Searching for periodic variations in these gave 362 detections over the mass range 0.15<~M/M_{sun}_<~0.7. The rotation period distributions were found to show a remarkable morphology as a function of mass, with the fastest rotators bounded by P>0.25d, and the slowest rotators for M<~0.5M_{sun}_ bounded by a line of P~M3, with those for M>~0.5M_{sun}_ following a flatter relation closer to P ~ constant. Models of the rotational evolution were investigated, finding that the evolution of the fastest rotators was well reproduced by a conventional solid body model with a mass-dependent saturation velocity, whereas core-envelope decoupling was needed to reproduce the evolution of the slowest rotators. None of our models were able to simultaneously reproduce the behaviour of both populations.
- ID:
- ivo://CDS.VizieR/J/MNRAS/383/1588
- Title:
- VIc photometry of NGC 2547 low-mass stars
- Short Name:
- J/MNRAS/383/1588
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the results of an I-band time-series photometric survey of NGC 2547 using the MPG/ESO 2.2-m telescope with Wide Field Imager, achieving better than 1 per cent photometric precision per data point over 14~<I~<18. Candidate cluster members were selected from a V versus V-I colour-magnitude diagram over 12.5<V<24 (covering masses from 0.9M_{sun}_ down to below the brown dwarf limit), finding 800 candidates, of which we expect ~330 to be real cluster members, taking into account contamination from the field (which is most severe at the extremes of our mass range). Searching for periodic variations in these gave 176 detections over the mass range 0.1~<M/M_{sun}_<0.9.
- ID:
- ivo://CDS.VizieR/J/AcA/57/249
- Title:
- VIc photometry of NGC 6755 stars
- Short Name:
- J/AcA/57/249
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results from a search for variable stars in the field of a young open cluster NGC 6755. Altogether seventy one variable stars have been discovered. Thirty one of them are eclipsing systems. This group contains ten EA, four EB and seventeen EW-type systems. Photometric variability of four late type stars is most probably caused by their chromospherical activity. Another seven detected variable stars have light curves typical for pulsating stars from the main instability strip. Four of them we tentatively classified as gamma Dor, one as delta Sct and two as Population II Cepheid variable stars, respectively. Star designated as V40 can be either another population II Cepheid or an ellipsoidal binary system. The remaining twenty eight variable stars found in the field of this open cluster are most probably highly obscured background red giants (OSARG, irregular). For all detected variable stars we provide their light curves, preliminary classification, discussion on the possible cluster membership, equatorial coordinates, finding charts and periods when possible.
