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521. Hipparcos variable stars
ID:
ivo://CDS.VizieR/J/A+A/367/297
Title:
Hipparcos variable stars
Short Name:
J/A+A/367/297
Date:
21 Oct 2021
Publisher:
CDS
Description:
The data known as the Hipparcos Photometry obtained with the Hipparcos satellite have been investigated to find those stars which are least variable. Such stars are excellent candidates to serve as standards for photometric systems. Their spectral types suggest in which parts of the HR diagrams stars are most constant. In some cases these values strongly indicate that previous ground based studies claiming photometric variability are incorrect or that the level of stellar activity has changed.
522. Hopkins Ultraviolet Telescope
ID:
ivo://archive.stsci.edu/hut
Title:
Hopkins Ultraviolet Telescope
Short Name:
HUT
Date:
22 Jul 2020 21:30:05
Publisher:
Space Telescope Science Institute Archive
Description:
The Hopkins Ultraviolet Telescope (HUT) was a shuttle-borne instrument used to obtain ultraviolet spectra in the far ultraviolet region of the spectrum. It was part of the ASTRO payload complement of three co-mounted instruments that flew in December 1990 and March 1995 as Space Shuttle missions. More than 650 spectra were obtained of 340 targets. In April, 2013, the HUT data was reprocessed to improve calibration, expand metadata, add new data products, and update file formats. The current cone service uses the metadata from these reprocessed files.
523. Hot variable stars in NGC 330
ID:
ivo://CDS.VizieR/J/AJ/135/1350
Title:
Hot variable stars in NGC 330
Short Name:
J/AJ/135/1350
Date:
21 Oct 2021
Publisher:
CDS
Description:
In a sample of 150 hot stars in NGC 330, a SMC cluster containing a high fraction of Be stars, we searched for photometric variables using OGLE II data. At least one third of all stars are variable, with 38 being periodic. We found 27 pulsators ({lambda} Eri variables), six eclipsing systems, two bursting sources, and several stars with unusual photometric behavior. Pulsations are present in ~30% of known Be stars, and they are long lived, lasting more than a decade. The strongest pulsators are associated with stars evolved from the main sequence.
524. HR4796A dust ring Stokes images
ID:
ivo://CDS.VizieR/J/A+A/626/A54
Title:
HR4796A dust ring Stokes images
Short Name:
J/A+A/626/A54
Date:
21 Oct 2021
Publisher:
CDS
Description:
The scattering properties of the dust originating from debris discs are still poorly known. The analysis of scattered light is however a powerful remote-sensing tool to understand the physical properties of dust particles orbiting other stars. Scattered light is indeed widely used to characterise the properties of cometary dust in the solar system. We aim to measure the morphology and scattering properties of the dust from the debris ring around HR4796A in polarised optical light. We obtained high-contrast polarimetric images of HR4796A in the wavelength range 600-900nm with the SPHERE/ZIMPOL instrument on the Very Large Telescope. We measured for the first time the polarised phase function of the dust in a debris system over a wide range of scattering angles in the optical. We confirm that it is incompatible with dust particles being compact spheres under the assumption of the Mie theory, and propose alternative scenarios compatible with the observations, such as particles with irregular surface roughness or aggregate particles.
525. HR 1099 radial velocities
ID:
ivo://CDS.VizieR/J/A+A/429/309
Title:
HR 1099 radial velocities
Short Name:
J/A+A/429/309
Date:
21 Oct 2021
Publisher:
CDS
Description:
We studied orbital period changes in the non-eclipsing close binary HR 1099, one of the most bright members of the RS CVn class of magnetically active binary systems. Intermediate-resolution optical spectroscopy and IUE archive spectra were used to build radial-velocity curves yielding epochs of superior conjunction with an accuracy of 0.01 days. The final database ranged from 1976 to 2002 and allowed us a better assessment of the amplitude of the orbital period variation and its timescale.
526. HST/ACS one-year observations of M51 stars
ID:
ivo://CDS.VizieR/J/ApJ/864/111
Title:
HST/ACS one-year observations of M51 stars
Short Name:
J/ApJ/864/111
Date:
21 Oct 2021
Publisher:
CDS
Description:
Stellar photometric variability offers a novel probe of the interior structure and evolutionary state of stars. Here we present a census of stellar variability on day to decade timescales across the color-magnitude diagram (CMD) for 73000 stars brighter than M_I,814_=-5 in the Whirlpool Galaxy (M51). Our Cycle 24 Hubble Space Telescope (HST) program acquired V606- and I814-band images over 34 epochs spanning 1 year with pseudo-random cadences enabling sensitivity to periods from days to months. We supplement these data with archival V- and I-band HST data obtained in 1995 and 2005, providing sensitivity to variability on decade timescales. At least 50% of stars brighter than M_I,814_=-7 show strong evidence for variability within our Cycle 24 data; among stars with V_606_-I_814_>2 the variability fraction rises to ~100%. Large amplitude variability (>0.3mag) on decade timescales is restricted to red supergiants (RSGs) and very luminous blue stars. Both populations display fairly smooth variability on month-year timescales. The Cepheid instability strip is clearly visible in our data, although the variability fraction within this region never exceeds ~10%. The location of variable stars across the CMD broadly agrees with theoretical sources of variability, including the instability strip, RSG pulsational instabilities, long-period fundamental mode pulsations, and radiation-dominated envelopes in massive stars. Our data can be used to place stringent constraints on the precise onset of these various instabilities and their lifetimes and growth rates.
527. HST monitoring of flaring stars in the Galactic bulge
ID:
ivo://CDS.VizieR/J/ApJ/754/4
Title:
HST monitoring of flaring stars in the Galactic bulge
Short Name:
J/ApJ/754/4
Date:
21 Oct 2021
Publisher:
CDS
Description:
We utilize the Sagittarius Window Eclipsing Extrasolar Planet Search Hubble Space Telescope/Advanced Camera for Surveys data set for a Deep Rapid Archival Flare Transient Search (DRAFTS) to constrain the flare rate toward the older stellar population in the Galactic bulge. During seven days of monitoring 229293 stars brighter than V=29.5, we find evidence for flaring activity in 105 stars between V=20 and V=28. We divided the sample into non-variable stars and variable stars whose light curves contain large-scale variability. The flare rate on variable stars is ~700 times that of non-variable stars, with a significant correlation between the amount of underlying stellar variability and peak flare amplitude. The flare energy loss rates are generally higher than those of nearby well-studied single dMe flare stars.
528. HST observations for LMC Cepheids
ID:
ivo://CDS.VizieR/J/ApJ/876/85
Title:
HST observations for LMC Cepheids
Short Name:
J/ApJ/876/85
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present an improved determination of the Hubble constant from Hubble Space Telescope (HST) observations of 70 long-period Cepheids in the Large Magellanic Cloud (LMC). These were obtained with the same WFC3 photometric system used to measure extragalactic Cepheids in the hosts of SNe Ia. Gyroscopic control of HST was employed to reduce overheads while collecting a large sample of widely separated Cepheids. The Cepheid period-luminosity relation provides a zero-point-independent link with 0.4% precision between the new 1.2% geometric distance to the LMC from detached eclipsing binaries (DEBs) measured by Pietrzynski+ (2019Natur.567..200P) and the luminosity of SNe Ia. Measurements and analysis of the LMC Cepheids were completed prior to knowledge of the new DEB LMC distance. Combined with a refined calibration of the count-rate linearity of WFC3-IR with 0.1% precision, these three improved elements together reduce the overall uncertainty in the geometric calibration of the Cepheid distance ladder based on the LMC from 2.5% to 1.3%. Using only the LMC DEBs to calibrate the ladder, we find H_0_=74.22+/-1.82km/s/Mpc including systematic uncertainties, 3% higher than before for this particular anchor. Combining the LMC DEBs, masers in NGC 4258, and Milky Way parallaxes yields our best estimate: H_0_=74.03+/-1.42km/s/Mpc, including systematics, an uncertainty of 1.91%-15% lower than our best previous result. Removing any one of these anchors changes H0 by less than 0.7%. The difference between H0 measured locally and the value inferred from Planck CMB and {Lambda}CDM is 6.6+/-1.5km/s/Mpc or 4.4{sigma} (P=99.999% for Gaussian errors) in significance, raising the discrepancy beyond a plausible level of chance. We summarize independent tests showing that this discrepancy is not attributable to an error in any one source or measurement, increasing the odds that it results from a cosmological feature beyond {Lambda}CDM.
529. HST observations of 7 Pop.II variable stars
ID:
ivo://CDS.VizieR/J/AJ/142/187
Title:
HST observations of 7 Pop.II variable stars
Short Name:
J/AJ/142/187
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present new absolute trigonometric parallaxes and proper motions for seven Population II variable stars - five RR Lyr variables: RZ Cep, XZ Cyg, SU Dra, RR Lyr, and UV Oct; and two type 2 Cepheids: VY Pyx and {kappa} Pav. We obtained these results with astrometric data from Fine Guidance Sensors, white-light interferometers on Hubble Space Telescope. We find absolute parallaxes in milliseconds of arc: RZ Cep, 2.12+/-0.16mas; XZ Cyg, 1.67+/-0.17mas; SU Dra, 1.42+/-0.16mas; RR Lyr, 3.77+/-0.13mas; UV Oct, 1.71+/-0.10mas; VY Pyx, 6.44+/-0.23mas; and {kappa} Pav, 5.57+/-0.28mas; an average {sigma}_{pi}_/{pi}=5.4%. With these parallaxes, we compute absolute magnitudes in V and K bandpasses corrected for interstellar extinction and Lutz-Kelker-Hanson bias. Using these RR Lyrae variable star absolute magnitudes, we then derive zero points for M_V_-[Fe/H] and M_K_-[Fe/H]-logP relations. The technique of reduced parallaxes corroborates these results. We employ our new results to determine distances and ages of several Galactic globular clusters and the distance of the Large Magellanic Cloud. The latter is close to that previously derived from Classical Cepheids uncorrected for any metallicity effect, indicating that any such effect is small. We also discuss the somewhat puzzling results obtained for our two type 2 Cepheids.
530. HST obs. of Mira candidates in NGC 4258
ID:
ivo://CDS.VizieR/J/ApJ/857/67
Title:
HST obs. of Mira candidates in NGC 4258
Short Name:
J/ApJ/857/67
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present year-long, near-infrared (NIR) Hubble Space Telescope (HST) WFC3 observations of Mira variables in the water megamaser host galaxy NGC 4258. Miras are asymptotic giant branch variables that can be divided into oxygen- (O-) and carbon- (C-) rich subclasses. Oxygen-rich Miras follow a tight (scatter ~0.14mag) period-luminosity relation (PLR) in the NIR and can be used to measure extragalactic distances. The water megamaser in NGC 4258 gives a geometric distance to the galaxy accurate to 2.6% that can serve to calibrate the Mira PLR. We develop criteria for detecting and classifying O-rich Miras with optical and NIR data as well as NIR data alone. In total, we discover 438 Mira candidates that we classify with high confidence as O-rich. Our most stringent criteria produce a sample of 139 Mira candidates that we use to measure a PLR. We use the OGLE-III sample of O-rich Miras in the Large Magellanic Cloud to obtain a relative distance modulus, {mu}_4258_-{mu}_LMC_=10.95+/-0.01 (statistical) +/-0.06 (systematic) mag, that is statistically consistent with the relative distance determined using Cepheids. These results demonstrate the feasibility of discovering and characterizing Miras using the NIR with the HST and the upcoming James Webb Space Telescope and using those Miras to measure extragalactic distances and determine the Hubble constant.