Abstract
We present newly calibrated period–
ϕ
31
–Fe/H relations for fundamental-mode RR Lyrae stars in the optical and, for the first time, mid-infrared. This work’s calibration data set provides ...the largest and most comprehensive span of parameter space to date, with homogeneous metallicities from −3 ≲ Fe/H ≲ 0.4 and accurate Fourier parameters derived from 1980 ASAS-SN (
V
band) and 1083 WISE (NEOWISE extension,
W
1 and
W
2 bands) RR Lyrae stars with well-sampled light curves. We compare our optical period–
ϕ
31
–Fe/H relation with those available in the literature and demonstrate that our relation minimizes systematic trends in the lower and higher metallicity range. Moreover, a direct comparison shows that our optical photometric metallicities are consistent with both those from high-resolution spectroscopy and globular clusters, supporting the good performance of our relation. We found an intrinsic scatter in the photometric metallicities (0.41 dex in the
V
band and 0.50 dex in the infrared) by utilizing large calibration data sets covering a broad metallicity range. This scatter becomes smaller when optical and infrared bands are used together (0.37 dex). Overall, the relations derived in this work have many potential applications, including large-area photometric surveys with James Webb Space Telescope in the infrared and LSST in the optical.
Abstract
The possible existence of stellar halos in low-mass galaxies is being intensely discussed nowadays after some recent discoveries of stars located in the outskirts of dwarf galaxies of the ...Local Group. RR Lyrae stars can be used to identify the extent of these structures, taking advantage of the minimization of foreground contamination they provide. In this work we use RR Lyrae stars obtained from Gaia DR3, the Dark Energy Survey, the Zwicky Transient Facility, and Pan-STARRS1 to explore the outskirts of 45 ultrafaint dwarf galaxies. We associate the stars with a host galaxy based on their angular separations, magnitudes, and proper motions. We find a total of 120 RR Lyrae stars that belong to 21 different galaxies in our sample. We report seven new RR Lyrae stars in six ultrafaint dwarf galaxies (Hydrus I, Ursa Major I, Ursa Major II, Grus II, Eridanus II, and Tucana II). We found a large number of new possible members in Bootes I and Bootes III as well, but some of them may actually belong to the nearby Sagittarius stream. Adding to our list of 120 RR Lyrae stars the observations of other ultrafaint dwarf galaxies that were beyond the reach of our search, we find that at least 10 of these galaxies have RR Lyrae stars located at distances greater than four times their respective half-light radius, which implies that at least 33% of the 30 ultrafaint dwarfs with a population of RR Lyrae stars have extended stellar populations.
ABSTRACT
Accurate metallicities of RR Lyrae are extremely important in constraining period–luminosity–metallicity (PLZ) relationships, particularly in the near-infrared. We analyse 69 high-resolution ...spectra of Galactic RR Lyrae stars from the Southern African Large Telescope. We measure metallicities of 58 of these RR Lyrae stars with typical uncertainties of 0.15 dex. All but one RR Lyrae in this sample has accurate ($\sigma _{\varpi }\lesssim 10{{\ \rm per\ cent}}$) parallax from Gaia. Combining these new high-resolution spectroscopic abundances with similar determinations from the literature for 93 stars, we present new PLZ relationships in WISE W1 and W2 magnitudes, and the Wesenheit magnitudes W(W1, V − W1) and W(W2, V − W2).
Abstract
We present new empirical infrared period–luminosity–metallicity (PLZ) and period–Wesenheit–metallicity (PWZ) relations for RR Lyae based on the latest Gaia Early Data Release 3 (EDR3) ...parallaxes. The relations are provided in the Wide-field Infrared Survey Explorer (WISE) W1 and W2 bands, as well as in the W(W1,
V
− W1) and W(W2,
V
− W2) Wesenheit magnitudes. The relations are calibrated using a very large sample of Galactic halo field RR Lyrae stars with homogeneous spectroscopic Fe/H abundances (over 1000 stars in the W1 band), covering a broad range of metallicities (−2.5 ≲ Fe/H ≲ 0.0). We test the performance of our PLZ and PWZ relations by determining the distance moduli of both galactic and extragalactic stellar associations: the Sculptor dwarf spheroidal galaxy in the Local Group (finding
μ
¯
0
=
19.47
±
0.06
), the Galactic globular clusters M4 (
μ
¯
0
=
11.16
±
0.05
), and the Reticulum globular cluster in the Large Magellanic Cloud (
μ
¯
0
=
18.23
±
0.06
). The distance moduli determined through all our relations are internally self-consistent (within ≲0.05 mag) but are systematically smaller (by ∼2–3
σ
) than previous literature measurements taken from a variety of methods/anchors. However, a comparison with similar recent RR Lyrae empirical relations anchored with EDR3 likewise shows, to varying extents, a systematically smaller distance modulus for PLZ/PWZ RR Lyrae relations.
Old-aged stellar distance indicators are present in all Galactic structures (halo, bulge, disk) and in galaxies of all Hubble types and, thus, are immensely powerful tools for understanding our ...Universe. Here we present a comprehensive review for three primary standard candles from Population II: (i) RR Lyrae type variables (RRL), (ii) type II Cepheid variables (T2C), and (iii) the tip of the red giant branch (TRGB). The discovery and use of these distance indicators is placed in historical context before describing their theoretical foundations and demonstrating their observational applications across multiple wavelengths. The methods used to establish the absolute scale for each standard candle is described with a discussion of the observational systematics. We conclude by looking forward to the suite of new observational facilities anticipated over the next decade; these have both a broader wavelength coverage and larger apertures than current facilities. We anticipate future advancements in our theoretical understanding and observational application of these stellar populations as they apply to the Galactic and extragalactic distance scale.
Abstract
We report 350 pulsating variable stars found in four DECam fields (∼12 deg
2
) covering the Antlia 2 satellite galaxy. The sample of variables includes 318 RR Lyrae stars and eight anomalous ...Cepheids in the galaxy. Reclassification of several objects designated previously to be RR Lyrae as anomalous Cepheids get rid of the satellite’s stars intervening along the line of sight. This in turn removes the need for prolific tidal disruption of the dwarf, in agreement with the recently updated proper motion and pericenter measurements based on Gaia EDR3. There are also several bright foreground RR Lyrae stars in the field, and two distant background variables located ∼45 kpc behind Antlia 2. We found RR Lyrae stars over the full search area, suggesting that the galaxy is very large and likely extends beyond our observed area. The mean period of the RR
ab
in Antlia 2 is 0.599 days, while the RR
c
have a mean period of 0.368 days, indicating the galaxy is an Oosterhoff-intermediate system. The distance to Antlia 2 based on the RR Lyrae stars is 124.1 kpc (
μ
0
= 20.47) with a dispersion of 5.4 kpc. We measured a clear distance gradient along the semimajor axis of the galaxy, with the southeast side of Antlia 2 being ∼13 kpc farther away from the northwest side. This elongation along the line of sight is likely due to the ongoing tidal disruption of Ant 2.
Abstract
We present a census of variable stars in six M31 dwarf spheroidal satellites observed with the
Hubble Space Telescope
. We detect 870 RR Lyrae (RRL) stars in the fields of And I (296), II ...(251), III (111), XV (117), XVI (8), and XXVIII (87). We also detect a total of 15 Anomalous Cepheids, three eclipsing binaries, and seven field RRL stars compatible with being members of the M31 halo or the Giant Stellar Stream. We derive robust and homogeneous distances to the six galaxies using different methods based on the properties of the RRL stars. Working with the up-to-date set of Period-Wesenheit (
I
,
B
–
I
) relations published by Marconi et al., we obtain distance moduli of
μ
0
= 24.49, 24.16, 24.36, 24.42, 23.70, 24.43 mag (respectively), with systematic uncertainties of 0.08 mag and statistical uncertainties <0.11 mag. We have considered an enlarged sample of 16 M31 satellites with published variability studies, and compared their pulsational observables (e.g., periods and amplitudes) with those of 15 Milky Way satellites for which similar data are available. The properties of the (strictly old) RRL in both satellite systems do not show any significant difference. In particular, we found a strikingly similar correlation between the mean period distribution of the fundamental RRL pulsators (RRab) and the mean metallicities of the galaxies. This indicates that the old RRL progenitors were similar at the early stage in the two environments, suggesting very similar characteristics for the earliest stages of evolution of both satellite systems.
Abstract
We present new period-
ϕ
31
-Fe/H relations for first-overtone RRL stars (RRc), calibrated over a broad range of metallicities (−2.5 ≲ Fe/H ≲ 0.0) using the largest currently available set ...of Galactic halo field RRL with homogeneous spectroscopic metallicities. Our relations are defined in the optical (ASAS-SN
V
band) and, inaugurally, in the infrared (WISE
W1
and
W2
bands). Our
V
-band relation can reproduce individual RRc spectroscopic metallicities with a dispersion of 0.30 dex over the entire metallicity range of our calibrator sample (an rms smaller than what we found for other relations in literature including nonlinear terms). Our infrared relation has a similar dispersion in the low- and intermediate-metallicity range (Fe/H ≲ −0.5), but tends to underestimate the Fe/H abundance around solar metallicity. We tested our relations by measuring both the metallicity of the Sculptor dSph and a sample of Galactic globular clusters, rich in both RRc and RRab stars. The average metallicity we obtain for the combined RRL sample in each cluster is within ±0.08 dex of their spectroscopic metallicities. The infrared and optical relations presented in this work will enable deriving reliable photometric RRL metallicities in conditions where spectroscopic measurements are not feasible; e.g., in distant galaxies or reddened regions (observed with upcoming Extremely Large Telescopes and the James Webb Space Telescope), or in the large sample of new RRL that will be discovered in large-area time-domain photometric surveys (such as the LSST and the Roman space telescope).
Abstract
The Initial Star formation and Lifetimes of Andromeda Satellites (ISLAndS) project employs
Hubble Space Telescope
imaging to study a representative sample of six Andromeda dSph satellite ...companion galaxies. Our main goal is to determine whether the star formation histories (SFHs) of the Andromeda dSph satellites demonstrate significant statistical differences from those of the Milky Way (MW). Our deep observations yield a time resolution at the oldest ages of ∼1 Gyr, allowing meaningful comparisons to the MW satellites. The six dSphs present a variety of SFHs (e.g., a significant range in quenching times,
τ
q
, from 9 to 6 Gyr ago) that are not strictly correlated with luminosity or present distance from M31. In agreement with observations of MW companions of similar mass, there is no evidence of complete quenching of star formation by the cosmic UV background responsible for reionization, but the possibility of a degree of quenching at reionization cannot be ruled out. We do not find significant differences between the SFHs of the members and non-members of the vast, thin plane of satellites. The SFHs of the ISLAndS M31 dSphs appear to be more uniform than those of the MW dSphs. Specifically, the primary difference between the SFHs of the ISLAndS dSphs and MW dSph companions of similar luminosities and host distances is the absence of late-quenching (
τ
q
≤
5
Gyr
) dSphs in the ISLAndS sample. Thus, models that can produce satellite populations with and without late-quenching satellites are of extreme interest.
Accurate astronomical distance determination is crucial for all fields in astrophysics, from Galactic to cosmological scales. Despite, or perhaps because of, significant efforts to determine accurate ...distances, using a wide range of methods, tracers, and techniques, an internally consistent astronomical distance framework has not yet been established. We review current efforts to homogenize the Local Group’s distance framework, with particular emphasis on the potential of RR Lyrae stars as distance indicators, and attempt to extend this in an internally consistent manner to cosmological distances. Calibration based on Type Ia supernovae and distance determinations based on gravitational lensing represent particularly promising approaches. We provide a positive outlook to improvements to the status quo expected from future surveys, missions, and facilities. Astronomical distance determination has clearly reached maturity and near-consistency.
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