- 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.
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- 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.
- 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.
- 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.
- 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.
- ID:
- ivo://CDS.VizieR/J/ApJ/889/5
- Title:
- HST obs. of Mira variables in the SNIa host NGC1559
- Short Name:
- J/ApJ/889/5
- Date:
- 17 Jan 2022 11:46:55
- Publisher:
- CDS
- Description:
- We present year-long, near-infrared Hubble Space Telescope (HST) WFC3 observations used to search for Mira variables in NGC 1559, the host galaxy of the Type Ia supernova (SN Ia) SN 2005df. This is the first dedicated search for Miras, highly evolved low-mass stars, in an SNIa host, and subsequently the first calibration of the SN Ia luminosity using Miras in a role historically played by Cepheids. We identify a sample of 115 O-rich Miras with P<400days based on their light-curve properties. We find that the scatter in the Mira period-luminosity relation (PLR) is comparable to Cepheid PLRs seen in SN Ia host galaxies. Using a sample of O-rich Miras discovered in NGC 4258 with HSTF160W and its maser distance, we measure a distance modulus for NGC1559 of {mu}_1559_=31.41+/-0.050(statistical)+/-0.060(systematic)mag. Based on the light curve of the normal, well-observed, low-reddening SN 2005df, we obtain a measurement of the fiducial SN Ia absolute magnitude of M_B_^0^=-19.27+/-0.13mag. With the Hubble diagram of SNe Ia we find H_0_=72.7+/-4.6km/s/Mpc. Combining the calibration from the NGC 4258 megamaser and the Large Magellanic Cloud detached eclipsing binaries gives a best value of H_0_=73.3+/-4.0km/s/Mpc. This result is within 1{sigma} of the Hubble constant derived using Cepheids and multiple calibrating SNe Ia. This is the first of four expected calibrations of the SN Ia luminosity from Miras that should reduce the error in H_0_ via Miras to ~3%. In light of the present Hubble tension and JWST, Miras have utility in the extragalactic distance scale to check Cepheid distances or calibrate nearby SNe in early-type host galaxies that would be unlikely targets for Cepheid searches.
- ID:
- ivo://CDS.VizieR/J/ApJ/902/26
- Title:
- HST opt. & H-band obs. of Cepheids in NGC4151
- Short Name:
- J/ApJ/902/26
- Date:
- 14 Mar 2022 07:44:50
- Publisher:
- CDS
- Description:
- We derive a distance of 15.8+/-0.4Mpc to the archetypal Seyfert 1 galaxy NGC 4151 based on the near-infrared Cepheid period-luminosity relation and new Hubble Space Telescope multiband imaging. This distance determination, based on measurements of 35 long-period (P>25d) Cepheids, will support the absolute calibration of the supermassive black hole mass in this system, as well as studies of the dynamics of the feedback or feeding of its active galactic nucleus.
- ID:
- ivo://CDS.VizieR/J/ApJ/777/79
- Title:
- HST photometry of Cepheid candidates in M101
- Short Name:
- J/ApJ/777/79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The impact of metallicity on the Cepheid period-luminosity (P-L) relation is investigated using Hubble Space Telescope Advanced Camera for Surveys V and I images of M101. Variations in the reddening-free Wesenheit parameter (W), which is employed as a proxy for luminosity, are examined as a function of the radial distance from the center of M101 (and thus metallicity). We determine that there is no dependence of the slope on metallicity. However, the intercept is found to depend on metallicity by {gamma}_VI_=-0.33+/-0.12mag.dex^-1^ and {gamma}_VI_=-0.71+/-0.17mag.dex^-1^ using 2{sigma} and 3{sigma} rejection criteria, respectively. Sigma-clipping impacts the derived metallicity dependence, and the 2{sigma} criterion applied likely mitigates blending, particularly in the crowded inner regions of M101. A metallicity-corrected distance for M101 is obtained from 619 Cepheids ({mu}=28.96+/-0.11), a result that agrees with the recently determined SN Ia distance. The metallicity effects described can be bypassed by working at near and mid-infrared wavelengths (e.g., the Carnegie Hubble Program).
- 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.
- 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.
