- ID:
- ivo://CDS.VizieR/J/ApJ/756/108
- Title:
- HST VI photometry of variable stars in Leo T
- Short Name:
- J/ApJ/756/108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from the first combined study of variable stars and star formation history (SFH) of the Milky Way "ultra-faint" dwarf (UFD) galaxy Leo T, based on F606W and F814W multi-epoch archive observations obtained with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. We have detected 14 variable stars in the galaxy. They include one fundamental-mode RR Lyrae star and 11 Anomalous Cepheids with periods shorter than 1 day, thus suggesting the occurrence of multiple star formation episodes in this UFD, of which one about 10 Gyr ago produced the RR Lyrae star. A new estimate of the distance to Leo T of 409^+29^_-27_kpc (distance modulus of 23.06+/-0.15mag) was derived from the galaxy's RR Lyrae star. Our V, V-I color-magnitude diagram (CMD) of Leo T reaches V~29mag and shows features typical of a galaxy in transition between dwarf irregular and dwarf spheroidal types. A quantitative analysis of the SFH, based on the comparison of the observed V, V-I CMD with the expected distribution of stars for different evolutionary scenarios, confirms that Leo T has a complex SFH dominated by two enhanced periods about 1.5 and 9 Gyr ago, respectively. The distribution of stars and gas shows that the galaxy has a fairly asymmetric structure.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/730/119
- Title:
- HST/WFC3 observations of Cepheids in SN Ia hosts
- Short Name:
- J/ApJ/730/119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to determine the Hubble constant from optical and infrared observations of over 600 Cepheid variables in the host galaxies of eight recent Type Ia supernovae (SNe Ia), providing the calibration for a magnitude-redshift relation based on 253 SNe Ia.
- ID:
- ivo://CDS.VizieR/J/ApJ/826/56
- Title:
- HST/WFC3 obs. of Cepheids in SN Ia host gal.
- Short Name:
- J/ApJ/826/56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%. The bulk of this improvement comes from new near-infrared (NIR) observations of Cepheid variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these in turn leverage the magnitude-redshift relation based on ~300 SNe Ia at z<0.15. All 19 hosts as well as the megamaser system NGC 4258 have been observed with WFC3 in the optical and NIR, thus nullifying cross-instrument zeropoint errors in the relative distance estimates from Cepheids. Other noteworthy improvements include a 33% reduction in the systematic uncertainty in the maser distance to NGC 4258, a larger sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW) Cepheids. We consider four geometric distance calibrations of Cepheids: (i) megamasers in NGC 4258, (ii) 8 DEBs in the LMC, (iii) 15 MW Cepheids with parallaxes measured with HST/FGS, HST/WFC3 spatial scanning and/or Hipparcos, and (iv) 2 DEBs in M31. The Hubble constant from each is 72.25+/-2.51, 72.04+/-2.67, 76.18+/-2.37, and 74.50+/-3.27km/s/Mpc, respectively. Our best estimate of H_0_=73.24+/-1.74km/s/Mpc combines the anchors NGC 4258, MW, and LMC, yielding a 2.4% determination (all quoted uncertainties include fully propagated statistical and systematic components). This value is 3.4{sigma} higher than 66.93+/-0.62km/s/Mpc predicted by {Lambda}CDM with 3 neutrino flavors having a mass of 0.06eV and the new Planck data, but the discrepancy reduces to 2.1{sigma} relative to the prediction of 69.3+/-0.7km/s/Mpc based on the comparably precise combination of WMAP+ACT+SPT+BAO observations, suggesting that systematic uncertainties in CMB radiation measurements may play a role in the tension. If we take the conflict between Planck high-redshift measurements and our local determination of H_0_ at face value, one plausible explanation could involve an additional source of dark radiation in the early universe in the range of {Delta}N_eff_~0.4-1. We anticipate further significant improvements in H_0_ from upcoming parallax measurements of long-period MW Cepheids.
- ID:
- ivo://CDS.VizieR/J/A+A/635/A66
- Title:
- Humps and bumps in RR Lyrae stars
- Short Name:
- J/A+A/635/A66
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the most extended and homogeneous study carried out so far of the main and early shocks in 1485 RR Lyrae stars in the Galactic bulge observed by the Optical Gravitational Lensing Experiment (OGLE). We selected nonmodulated fundamental-mode RR Lyrae stars with good-quality photometry. Using a self- developed method, we determined the centers and strengths of main and early shock features in the phased light curves. We found that the positions of both humps and bumps are highly correlated with the pulsation properties of the studied variables. Pulsators with a pronounced main shock are concentrated in the low-amplitude regime of the period-amplitude diagram, while stars with a strong early shock have average and above-average pulsation amplitudes. A connection between the main and early shocks and the Fourier coefficients is also observed. In the color-magnitude diagram (CMD), we see a separation between stars with strong and weak shocks. Variables with a pronounced main shock cluster close to the fundamental red edge of the instability strip (IS), while stars with a strong early shock tend to clump in the center and near the fundamental blue edge of the IS. The appearance of shocks and their properties appear to be independent of the direction of evolution estimated from the period change rate of the studied stars. In addition, the differences in the period change rate between the two main Oosterhoff groups found in the Galactic bulge suggest that stars of Oosterhoff type I are located close to the zero-age horizontal branch while Oosterhoff type II variables are on their way toward the fundamental red edge of the instability strip, and have therefore already left the zero-age horizontal branch.
- ID:
- ivo://CDS.VizieR/J/A+A/592/A117
- Title:
- HU Vir radial velocities and VI light curves
- Short Name:
- J/A+A/592/A117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the differential surface rotation on the primary star of the RS CVn binary HU Vir by tracking its starspot distribution as a function of time. We also recompute and update the values for several system parameters of the triple system HU Vir (close and wide orbits). Spectroscopic observations were carried out with the STELLA echelle spectrograph (SES) at the robotic 1.2-m STELLA-I telescope at the Observatorio del Teide in Tenerife, Spain. A time series of 118 echelle spectra was taken in the period between Feb 17 to Jun 26, 2013. Nine consecutive Doppler images were reconstructed from these data, using our line-profile inversion code iMap. An image cross-correlation method was applied to derive the surface differential-rotation law for HU Vir. New orbital elements for the close and the wide orbits were computed using our new STELLA RVs combined with the RV data available in the literature. Photometric observations were performed with the Amadeus Automatic Photoelectric Telescope (APT) at Fairborn Observatory in southern Arizona starting in 1996, providing contemporaneous Johnson-Cousins V and I data for approximately 20 years. This data was used to determine the stellar rotation period and the active longitudes.
- ID:
- ivo://CDS.VizieR/J/A+A/542/A89
- Title:
- Hvar survey for roAp stars. I.
- Short Name:
- J/A+A/542/A89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The rapidly oscillating Ap (roAp) stars exhibit short time scale photometric and/or radial velocity variations, which are most important to test current pulsation models as well as our assumptions of the atmospheric structure characteristics. In addition, their chemical peculiarity makes them very interesting for probing stellar formation and evolution in the presence of a global magnetic field. To date, only a limited number of about 45 roAp stars are known. In order to increase the sample, we obtained photometric time series of 20 good roAp candidates to search for pulsations. We present the time series analysis of about 60 hours of CCD photometry taken at the 1 meter Austrian-Croatian Telescope (Hvar Observatory) and derive effective temperatures for the programme objects. The upper amplitude limits of the Fourier spectra are typically below 2mmag in Bessell B with one good candidate for follow-up observations to find possible pulsation. In addition, we present a list of further roAp candidates, worth to be (re)investigated.
- ID:
- ivo://CDS.VizieR/J/AJ/152/164
- Title:
- I-band light curves of OGLE LMC Miras
- Short Name:
- J/AJ/152/164
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We develop a nonlinear semi-parametric Gaussian process model to estimate periods of Miras with sparsely sampled light curves. The model uses a sinusoidal basis for the periodic variation and a Gaussian process for the stochastic changes. We use maximum likelihood to estimate the period and the parameters of the Gaussian process, while integrating out the effects of other nuisance parameters in the model with respect to a suitable prior distribution obtained from earlier studies. Since the likelihood is highly multimodal for period, we implement a hybrid method that applies the quasi-Newton algorithm for Gaussian process parameters and search the period/frequency parameter space over a dense grid. A large-scale, high-fidelity simulation is conducted to mimic the sampling quality of Mira light curves obtained by the M33 Synoptic Stellar Survey. The simulated data set is publicly available and can serve as a testbed for future evaluation of different period estimation methods. The semi-parametric model outperforms an existing algorithm on this simulated test data set as measured by period recovery rate and quality of the resulting period-luminosity relations.
- ID:
- ivo://CDS.VizieR/J/AJ/158/16
- Title:
- Identification of RR Lyrae stars from the DES
- Short Name:
- J/AJ/158/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Many studies have shown that RR Lyrae variable stars (RRL) are powerful stellar tracers of Galactic halo structure and satellite galaxies. The Dark Energy Survey (DES), with its deep and wide coverage (g~23.5 mag in a single exposure; over 5000 deg^2^) provides a rich opportunity to search for substructures out to the edge of the Milky Way halo. However, the sparse and unevenly sampled multiband light curves from the DES wide-field survey (a median of four observations in each of grizY over the first three years) pose a challenge for traditional techniques used to detect RRL. We present an empirically motivated and computationally efficient template-fitting method to identify these variable stars using three years of DES data. When tested on DES light curves of previously classified objects in SDSS stripe 82, our algorithm recovers 89% of RRL periods to within 1% of their true value with 85% purity and 76% completeness. Using this method, we identify 5783 RRL candidates, ~28% of which are previously undiscovered. This method will be useful for identifying RRL in other sparse multiband data sets.
- ID:
- ivo://CDS.VizieR/J/A+A/559/A97
- Title:
- II Pegasus photometry during 1979-2010
- Short Name:
- J/A+A/559/A97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- According to earlier Doppler images of the magnetically active primary giant component of the RS CVn binary II Peg, the surface of the star was dominated by one single active longitude that was clearly drifting in the rotational frame of the binary system during 1994-2002; later imaging for 2004-2010, however, showed decreased and chaotic spot activity, with no signs of the drift pattern. Here we set out to investigate from a more extensive photometric dataset whether such a drift is a persistent phenomenon, in which case it could be due to either an azimuthal dynamo wave or an indication of the binary system orbital synchronization still being incomplete. We analyse the datasets using the Carrier Fit method (hereafter CF), especially suitable for analyzing time series in which a fast clocking frequency (such as the rotation of the star) is modulated with a slower process (such as the stellar activity cycle).
- ID:
- ivo://CDS.VizieR/J/A+A/362/215
- Title:
- IJKs photometry of Galactic bulge variables
- Short Name:
- J/A+A/362/215
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Repeated DENIS observations (summer 1996 & 1998) in the J (1.25{mu}m) and the K_s_ (2.15{mu}m) bands are used to look for variables stars. We present two catalogues of ~1000 probable variables in an area of ~4deg^2^ of the inner galactic bulge. The first one contains ~720 variable star candidates which which show variability in the J and K_s_ while the second consists of sources only observed to be variable in K_s_ (~270 sources), mainly in regions whit high interstellar extinction.