- ID:
- ivo://CDS.VizieR/J/MNRAS/465/2489
- Title:
- NGC 6401 bulge variable stars
- Short Name:
- J/MNRAS/465/2489
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of variable stars in globular cluster NGC 6401. The cluster is only 5.3{deg} away from the Galactic Centre and suffers from strong differential reddening. The photometric precision afforded us by difference image analysis resulted in improved sensitivity to variability in formerly inaccessible interior regions of the cluster. We find 23 RRab and 11 RRc stars within one cluster radius (2.4-arcmin), for which we provide coordinates, finder-charts and time series photometry. Through Fourier decomposition of the RR Lyrae star light curves we derive a mean metallicity of [Fe/H]UVES=-1.13+/-0.06 ([Fe/H]ZW=-1.25+/-0.06), and a distance of d~6.35+/-0.81kpc. Using the RR Lyrae population, we also determine that NGC 6401 is an Oosterhoff type I cluster.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/421/2998
- Title:
- NGC 6822 Cepheids JHKs light curves
- Short Name:
- J/MNRAS/421/2998
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent estimates of the Cepheid distance modulus of NGC 6822 differ by 0.18mag. To investigate this we present new multi-epoch JHKs photometry of classical Cepheids in the central region of NGC 6822 and show that there is a zero-point difference from earlier work. These data together with optical and mid-infrared observations from the literature are used to derive estimates of the distance modulus of NGC 6822. A best value of 23.40mag is adopted, based on a Large Magellanic Cloud (LMC) distance modulus of 18.50mag. The standard error of this quantity is ~0.05mag. We show that to derive consistent moduli from Cepheid observations at different wavelengths, it is necessary that the fiducial LMC period-luminosity relations at these wavelengths should refer to the same subsample of stars. Such a set is provided. A distance modulus based on RR Lyrae variables agrees with the Cepheid result.
- ID:
- ivo://CDS.VizieR/J/A+A/644/A16
- Title:
- NGC 6774 cool stars rotation periods
- Short Name:
- J/A+A/644/A16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Gyrochronology allows the derivation of ages for cool main sequence stars based on their observed rotation periods and masses, or a suitable proxy thereof. It is increasingly well-explored for FGK stars, but requires further measurements for older ages and K-M-type stars. We study the 2.7Gyr-old open cluster Ruprecht 147 to compare it with the previously-studied, but far more distant, NGC 6819 cluster, and especially to measure cooler stars than was previously possible there. We constructed an inclusive list of 102 cluster members from prior work, including Gaia DR2, and for which light curves were also obtained during Campaign 7 of the Kepler/K2 space mission. We placed them in the cluster color-magnitude diagram and checked the related information against appropriate isochrones. The light curves were then corrected for data systematics using Principal Component Analysis on all observed K2 C07 stars and subsequently subjected to periodicity analysis. Periodic signals are found for 32 stars, 21 of which are considered to be both highly reliable and to represent single, or effectively single, Ru 147 stars. These stars cover the spectral types from late-F to mid-M stars, and they have periods ranging from 6d-33d, allowing for a comparison of Ruprecht 147 to both other open clusters and to models of rotational spindown. The derived rotation periods connect reasonably to, overlap with, and extend to lower masses the known rotation period distribution of the 2.5 Gyr-old cluster NGC 6819. The data confirm that cool stars lie on a single surface in rotation period-mass-age space, and they simultaneously challenge its commonly assumed shape. The shape at the low mass region of the color-period diagram at the age of Ru 147 favors a recently-proposed model which requires a third mass-dependent timescale in addition to the two timescales required by a former model, suggesting that a third physical process is required to model rotating stars effectively.
- ID:
- ivo://CDS.VizieR/J/AJ/146/57
- Title:
- NGC 6402. I. BV photometry
- Short Name:
- J/AJ/146/57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present BV photometry of the Galactic globular cluster NGC 6402 (M14), based on 65 V frames and 67 B frames, reaching two magnitudes below the turnoff level. This represents, to the best of our knowledge, the deepest color-magnitude diagram (CMD) of NGC 6402 available in the literature. Statistical decontamination of field stars as well as differential reddening corrections are performed in order to derive a precise ridgeline and hence physical parameters of the cluster. We discuss previous attempts at deriving a reddening value for the cluster, and argue in favor of a value E(B-V)=0.57+/-0.02, which is significantly higher than indicated by either the Burstein & Heiles or Schlegel et al. (corrected according to Bonifacio et al.) interstellar dust maps. Differential reddening across the face of the cluster, which we find to be present at the level of {Delta}E(B-V){approx}0.17mag, is taken into account in our analysis. We measure several metallicity indicators based on the position of the red giant branch (RGB) in the cluster CMD. These give a metallicity of [Fe/H]=-1.38+/-0.07 on the Zinn & West scale and [Fe/H]=-1.28+/-0.08 on the new Carretta et al. (UVES) scale. We also provide measurements of other important photometric parameters for this cluster, including the position of the RGB luminosity function "bump" and the horizontal branch morphology. We compare the NGC 6402 ridgeline with that of NGC 5904 (M5) derived by Sandquist et al., and find evidence that NGC 6402 and M5 have approximately the same age to within the uncertainties, although the possibility that M14 may be slightly older cannot be ruled out.
- ID:
- ivo://CDS.VizieR/J/MNRAS/468/2816
- Title:
- NGC6397 low-mass variable stars
- Short Name:
- J/MNRAS/468/2816
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a photometric survey of the globular cluster NGC 6397 in a search for variable stars. We obtained ~11h of time-resolved photometric images with one European Southern Observatory-Very Large Telescope using the FOcal Reducer and low dispersion Spectrograph imager distributed over two consecutive nights. We analysed 8391 light curves of stars brighter than magnitude 23 with the 465-nm filter, and we identified 412 variable stars, reaching ~4.8+/-0.2 per cent of variability with time-scales between 0.004 and 2d, with amplitudes variation greater than +/-0.2mag.
- ID:
- ivo://CDS.VizieR/J/MNRAS/430/1433
- Title:
- NGC 2264 members periods with CoRoT
- Short Name:
- J/MNRAS/430/1433
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Rotation is one of the key stellar parameters which undergo substantial evolution during the stellar lifetime, in particular during the early stages. Stellar rotational periods can be determined on the basis of the periodic modulation of starlight produced by non-uniformities on the surface of the stars, due to manifestation of stellar activity. We present the results of an extensive search for rotational periods among NGC 2264 cluster members, based on photometric monitoring using the COnvection ROtation and planetary Transits (CoRoT) satellite, with particular attention to the distribution of classical and weak-line T-Tauri stars. NGC 2264 is one of the nearest and best studied star forming region in the solar neighbourhood, with an estimated age of 3Myr, and is the object of a recent simultaneous multiband campaign including a new CoRoT observation with the aim to assess the physical origin of the observed variability. We find that the rotational distributions of classical and weak-line T-Tauri stars are different, suggesting a difference in the rotational properties of accreting and non-accreting stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/420/1333
- Title:
- NGC 5024 (M53) RR Lyrae VI light curves
- Short Name:
- J/MNRAS/420/1333
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of amplitude and phase modulations typical of the Blazhko effect in 22 RRc and nine RRab type RR Lyrae stars in NGC 5024 (M53). This brings the confirmed Blazhko variables in this cluster to 23 RRc and 11 RRab stars, which represent 66 and 37 per cent of the total population of RRc and RRab stars in the cluster, respectively, making NGC 5024 the globular cluster with the largest presently known population of Blazhko RRc stars. We place a lower limit of 52 per cent on the overall incidence rate of the Blazhko effect among the RR Lyrae population in this cluster. New data have allowed us to refine the pulsation periods. The limitations imposed by the time span and sampling of our data prevent reliable estimations of the modulation periods. The amplitudes of the modulations range between 0.02 and 0.39mag. The RRab and RRc are neatly separated in the colour-magnitude diagram, and the RRc Blazhko variables are on average redder than their stable counterparts; these two facts may support the hypothesis that the horizontal branch (HB) evolution in this cluster is towards the red and that the Blazhko modulations in the RRc stars are connected with the pulsation mode switch.
- ID:
- ivo://CDS.VizieR/J/MNRAS/476/2813
- Title:
- NGC 2282 photometry of variable stars
- Short Name:
- J/MNRAS/476/2813
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report here CCD I-band time series photometry of a young (2-5Myr) cluster NGC 2282, in order to identify and understand the variability of pre-main-sequence (PMS) stars. The I-band photometry, down to ~20.5mag, enables us to probe the variability towards the lower mass end (~0.1M_{sun}_) of PMS stars. From the light curves of 1627 stars, we identified 62 new photometric variable candidates. Their association with the region was established from H{alpha} emission and infrared (IR) excess. Among 62 variables, 30 young variables exhibit H{alpha} emission, near-IR (NIR)/mid-IR (MIR) excess or both and are candidate members of the cluster. Out of 62 variables, 41 are periodic variables, with a rotation rate ranging from 0.2-7d. The period distribution exhibits a median period at ~1d, as in many young clusters (e.g. NGC 2264, ONC, etc.), but it follows a unimodal distribution, unlike others that have bimodality, with slow rotators peaking at ~6-8d. To investigate the rotation-disc and variability-disc connection, we derived the NIR excess from {Delta}(I-K) and the MIR excess from Spitzer [3.6]-[4.5]um data. No conclusive evidence of slow rotation with the presence of discs around stars and fast rotation for discless stars is obtained from our periodic variables. A clear increasing trend of the variability amplitude with IR excess is found for all variables.
- ID:
- ivo://CDS.VizieR/J/AcA/59/349
- Title:
- NGC 1502 UBVIc photometry
- Short Name:
- J/AcA/59/349
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of variability search in the field of the young open cluster NGC 1502. Eight variable stars were discovered. Of six other stars in the observed field that were suspected for variability, we confirm variability of two, including one beta Cep star, NGC 1502-26. The remaining four suspects were found to be constant in our photometry. In addition, UBVIc photometry of the well-known massive eclipsing binary SZ Cam was obtained.
- ID:
- ivo://CDS.VizieR/J/AJ/141/81
- Title:
- NGC 2419 variable star population
- Short Name:
- J/AJ/141/81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present B, V, and I CCD light curves for 101 variable stars belonging to the globular cluster NGC 2419, 60 of which are new discoveries, based on data sets obtained at the Telescopio Nazionale Galileo, the Subaru telescope, and the Hubble Space Telescope. The sample includes 75 RR Lyrae stars (38 RRab, 36 RRc, and one RRd), one Population II Cepheid, 12 SX Phoenicis variables, two delta Scuti stars, three binary systems, five long-period variables, and three variables of uncertain classification.
