Band Period-luminosity Research Articles

Stellar Variability and Distance Indicators in the Near-infrared in Nearby Galaxies. I. RR Lyrae and Anomalous Cepheids in Draco Dwarf Spheroidal

The Draco Dwarf spheroidal (dSph) galaxy is one of the nearest and the most dark-matter-dominated satellites of the Milky Way. We obtained multiepoch near-infrared (NIR, JHK s ) observations of the central region of Draco dSph covering a sky area of ∼21′ × 21′ using the WIRCam instrument at the 3.6 m Canada–France–Hawaii Telescope. Homogeneous JHK s time-series photometry for 212 RR Lyrae (173 fundamental-mode, 24 first-overtone, and 15 mixed-mode variables) and five Anomalous Cepheids in Draco dSph are presented and used to derive their period–luminosity relations at NIR wavelengths for the first-time. The small scatter of ∼0.05 mag in these empirical relations for RR Lyrae stars is consistent with those in globular clusters and suggests a very small metallicity spread, up to ∼0.2 dex, among these centrally located variables. Based on empirically calibrated NIR period–luminosity–metallicity relations for RR Lyrae in globular clusters, we determined a distance modulus to Draco dSph of μ RRL = 19.557 ± 0.026 mag. The calibrated K s -band period–luminosity relations for Anomalous Cepheids in the Draco dSph and the Large Magellanic Cloud exhibit statistically consistent slopes but systematically different zero points, hinting at possible metallicity dependence of ∼ − 0.3 mag dex−1. Finally, the apparent magnitudes of the tip of the red-giant branch in I and J bands also agree well with their absolute calibrations with the adopted RR Lyrae distance to Draco. Our recommended ∼1.5% precise RR Lyrae distance, D Draco = 81.55 ± 0.98(statistical) ± 1.17(systematic) kpc, is the most accurate and precise distance to Draco dSph galaxy.

Precise Empirical Determination of Metallicity Dependence of Near-infrared Period–Luminosity Relations for RR Lyrae Variables

RR Lyrae variables are excellent Population II distance indicators thanks to their well-defined period–luminosity relations (PLRs) at infrared wavelengths. We present results of near-infrared (NIR) monitoring of Galactic globular clusters to empirically quantify the metallicity dependence of NIR PLRs for RR Lyrae variables. Our sample includes homogeneous, accurate, and precise photometric data for 964 RR Lyrae variables in 11 globular clusters covering a large metallicity range (Δ[Fe/H] ∼ 2 dex). We derive JHK s -band period–luminosity–metallicity (PLZ) and period–Wesenheit–metallicity (PWZ) relations anchored using 346 Milky Way field RR Lyrae stars with Gaia parallaxes, and simultaneously solved for independent distances to globular clusters. We find a significant metallicity dependence of ∼0.2 mag dex−1 in the JHK s -band PLZ and PWZ relations for RR Lyrae stars independent of the adopted metallicity scale. The metallicity coefficients and the zero-points of the empirical PLZ and PWZ relations are in excellent agreement with the predictions from the horizontal branch evolution and pulsation models. Furthermore, RR Lyrae–based distances to our sample of globular clusters are also statistically consistent with other independent measurements in the literature. Our recommended empirical JHK s -band PLZ relations for RR Lyrae stars with periods of fundamental mode pulsation (P f) are: MJ=−0.44(±0.03)−1.83(±0.02)log(Pf)+0.20(±0.02)[Fe/H](σ=0.05mag)MH=−0.74(±0.02)−2.29(±0.02)log(Pf)+0.19(±0.01)[Fe/H](σ=0.05mag)MKs=−0.80(±0.02)−2.37(±0.02)log(Pf)+0.18(±0.01)[Fe/H](σ=0.05mag).

The period–luminosity relation of red supergiants with Gaia DR2

Abstract We revisit the K -band period–luminosity (P–L) relations of Galactic red supergiants using Gaia Data Release 2 parallaxes and up to 70 yr of photometry from AAVSO and ASAS campaigns. In addition, we examine 206 LMC red supergiants using 50 yr of photometric data from the digitized Harvard Astronomical Plate Collection. We identified periods by computing power spectra and calculated the period–luminosity relations of our samples and compared them with the literature. Newly available data tighten the P–L relations substantially. Identified periods form two groups: one with periods of 300–1000 d, corresponding to pulsations, and another with Long Secondary Periods between 1000 and 8000 d. Among the 48 Galactic objects we find shorter periods in 25 stars and long secondary periods in 23 stars. In the LMC sample we identify 85 and 94 red supergiants with shorter and long secondary periods, respectively. The P–L relation of the Galactic red supergiants is in agreement with the red supergiants in both, the Large Magellanic Cloud and the Andromeda galaxy. We find no clear continuity between the known red giant period–luminosity sequences, and the red supergiant sequences investigated here.

Variable stars in local group galaxies – IV. RR Lyrae stars in the central regions of the low-density galaxy Crater II

We present a search and analysis of variable stars in the recently discovered Crater~II dwarf galaxy. Based on $B$, $V$, $I$ data collected with the Isaac Newton Telescope (FoV$\sim$0.44 square degrees) we detected 37 variable stars, of which 34 are bone-fide RR Lyrae stars of Crater~II (28 RRab, 4 RRc, 2 RRd). We applied the metal-independent ($V$, $B-V$) Period--Wesenheit relation and derived a true distance modulus ($\mu$ = 20.30$\pm$0.08 mag ($\sigma$=0.16 mag). Individual metallicities for RR Lyrae stars were derived by inversion of the predicted $I$-band Period-Luminosity relation. We find a mean metallicity of [Fe/H]=-1.64 and a standard deviation of $\sigma_{[Fe/H]}$ =0.21 dex, compatible with either negligible or vanishing intrinsic metallicity dispersion. The analysis of the Colour-Magnitude Diagram reveals a stark paucity of blue horizontal branch stars, at odds with other Galactic dwarfs, and globular clusters with similar metal abundances.

Galactic bulge population II Cepheids in the VVV survey: period-luminosity relations and a distance to the Galactic centre

We present the near-infrared observations of population II Cepheids in the Galactic bulge from VVV survey. We identify 340 population II Cepheids in the Galactic bulge from VVV survey based on their match with OGLE-III Catalogue. The single-epoch $JH$ and multi-epoch $K_s$ observations complement the accurate periods and optical $(VI)$ mean-magnitudes from OGLE. The sample consisting of BL Herculis and W Virginis subtypes is used to derive period-luminosity relations after correcting mean-magnitudes for the extinction. Our $K_s$-band period-luminosity relation, $K_s = -2.189(0.056)~[\log(P) - 1] + 11.187(0.032)$, is consistent with published work for BL Herculis and W Virginis variables in the Large Magellanic Cloud. We present a combined OGLE-III and VVV catalogue with periods, classification, mean magnitudes and extinction for 264 Galactic bulge population II Cepheids having good-quality $K_s$-band light curves. The absolute magnitudes for population II Cepheids and RR Lyraes calibrated using Gaia and Hubble Space Telescope parallaxes, together with calibrated magnitudes for Large Magellanic Cloud population II Cepheids, are used to obtain a distance to the Galactic center, $R_0=8.34\pm0.03{\mathrm{(stat.)}}\pm0.41{\mathrm{(syst.)}}$, which changes by $^{+ 0.05}_{-0.25}$ with different extinction laws. While noting the limitation of small number statistics, we find that the present sample of population II Cepheids in the Galactic bulge shows a nearly spheroidal spatial distribution, similar to metal-poor RR Lyrae variables. We do not find evidence of the inclined bar as traced by the metal-rich red-clump stars. The number density for population II Cepheids is more limited as compared to abundant RR Lyraes but they are bright and exhibit a wide range in period that provides a robust period-luminosity relation for an accurate estimate of the distance to the Galactic center.

Period–Luminosity relations derived from the OGLE-III first-overtone mode Cepheids in the Magellanic Clouds

We present multi-band Period-Luminosity (PL) relations for first-overtone mode Cepheids in the Small Magellanic Cloud (SMC). We derive optical band PL relations and the Wesenheit function using $VI$ mean magnitudes from the Optical Gravitational Lensing Experiment (OGLE-III) survey. We cross-match OGLE-III first-overtone mode Cepheids to the 2MASS and SAGE-SMC catalogs to derive PL relations at near-infrared ($JHK_s$) and mid-infrared ($3.6~\&~4.5\mu\mathrm{m}$) wavelengths. We test for possible non-linearities in these PL relations using robust statistical tests and find a significant break only in the optical-band PL relations at 2.5 days for first-overtone mode Cepheids. We do not find statistical evidence for a non-linearity in these PL relations at 1 day. The multi-band PL relations for fundamental-mode Cepheids in the SMC also exhibit a break at 2.5 days. We suggest that the period break around 2.5 days is related to sharp changes in the light curve parameters for SMC Cepheids. We also derive new optical and mid-infrared band PL relations for first-overtone mode Cepheids in the Large Magellanic Cloud (LMC). We compare multi-band PL relations for first-overtone mode Cepheids in the Magellanic Clouds and find a significant difference in the slope of the $V$-band PL relations but not for $I$-band PL relations. The slope of PL relations are found to be consistent in most of the infrared bands. A relative distance modulus of $\Delta\mu=0.49\pm0.02$~mag between the two clouds is estimated using multi-band PL relations for the first-overtone mode Cepheids in the SMC and LMC.

THE PERIOD-LUMINOSITY RELATION OF RED SUPERGIANT STARS IN THE SMALL MAGELLANIC CLOUD

The characteristics of light variation of RSGs in SMC are analyzed based on the nearly 8-10 year long data collected by the ASAS and MACHO projects. The identified 126 RSGs are classified into five categories accordingly: 20 with poor photometry, 55 with no reliable period, 6 with semi-regular variation, 15 with Long Secondary Period (LSP) and distinguishable short period and 30 with only LSP. For the semi-regular variables and the LSP variables with distinguishable short period, the Ks band period-luminosity (P-L) relation is analyzed and compared with that of the Galaxy, LMC and M33. It is found that the RSGs in these galaxies obey similar P-L relation except the Galaxy. In addition, the P-L relations in the infrared bands, namely the 2MASS JHKs, Spitzer/IRAC and Spitzer/MIPS 24 {\mu}m bands, are derived with high reliability. The best P-L relation occurs in the Spitzer/IRAC [3.6] and [4.5] bands. Based on the comparison with the theoretical calculation of the P-L relation, the mode of pulsation of RSGs in SMC is suggested to be the first overtone radial mode.

Preliminary results for RR Lyrae stars and Classical Cepheids from the Vista Magellanic Cloud (VMC) survey

The Vista Magellanic Cloud (VMC, PI M.R. Cioni) survey is collecting $K_S$-band time series photometry of the system formed by the two Magellanic Clouds (MC) and the "bridge" that connects them. These data are used to build $K_S$-band light curves of the MC RR Lyrae stars and Classical Cepheids and determine absolute distances and the 3D geometry of the whole system using the $K$-band period luminosity ($PLK_S$), the period - luminosity - color ($PLC$) and the Wesenhiet relations applicable to these types of variables. As an example of the survey potential we present results from the VMC observations of two fields centered respectively on the South Ecliptic Pole and the 30 Doradus star forming region of the Large Magellanic Cloud. The VMC $K_S$-band light curves of the RR Lyrae stars in these two regions have very good photometric quality with typical errors for the individual data points in the range of $\sim$ 0.02 to 0.05 mag. The Cepheids have excellent light curves (typical errors of $\sim$ 0.01 mag). The average $K_S$ magnitudes derived for both types of variables were used to derive $PLK_S$ relations that are in general good agreement within the errors with the literature data, and show a smaller scatter than previous studies.

THE MID-INFRARED PERIOD-LUMINOSITY RELATIONS FOR THE SMALL MAGELLANIC CLOUD CEPHEIDS DERIVED FROMSPITZERARCHIVAL DATA

In this paper we derive the Spitzer IRAC band period-luminosity (P-L) relations for the Small Magellanic Cloud (SMC) Cepheids, by matching the Spitzer archival SAGE-SMC data with the OGLE-III SMC Cepheids. We find that the 3.6micron and 4.5micron band P-L relations can be better described using two P-L relations with a break period at log(P)=0.4: this is consistent with similar results at optical wavelengths for SMC P-L relations. The 5.8micron and 8.0micron band P-L relations do not extend to sufficiently short periods to enable a similar detection of a slope change at log(P)=0.4. The slopes of the SMC P-L relations, for log(P)>0.4, are consistent with their LMC counterparts that were derived from a similar dataset. They are also in agreement with those obtained from a small sample of Galactic Cepheids with parallax measurements.

The kinematics and zero-point of the log P-〈MK〉 relation for Galactic RR Lyrae variables via statistical parallax

We use accurate absolute proper motions and Two-Micron All-Sky Survey K s -band apparent magnitudes for 364 Galactic RR Lyrae variables to determine the kinematical parameters of the Galactic RR Lyrae population and constrain the zero-point of the K s -band period-luminosity relation for these stars via statistical parallax. We find the mean velocities of the halo- and thick-disc RR Lyrae populations in the solar neighbourhood to be [U o (Halo), V 0 (Halo), W 0 (Halo)] = (―12 ± 10, ―217 ± 9, ―6 ± 6) km s ―1 and [U 0 (Disc), V 0 (Disc), W 0 (Disc)] = (―15 ± 7, ―44 ± 7, ―25 ± 5) km s ―1 , respectively, and the corresponding components of the velocity-dispersion ellipsoids, [σ V R (Halo), σ V θ (Halo), σ W(Halo)] = (167 ± 9, 86 ± 6, 78 ± 5) km s ―1 and [σ V R (Disc), σ V θ (Disc), σ W(Disc)] = (55 ± 7, 44 ± 6, 30 ± 4) km s ―1 , respectively. The fraction of thick-disc stars is estimated at 0.25 ± 0.03. The corrected infrared period-luminosity relation is = ― 2.33 log P F ― 0.818 ± 0.081, implying a Large Magellanic Cloud (LMC) distance modulus of 18.27 ± 0.08 and a solar Galactocentric distance of 7.58 ± 0.40 kpc. Our results suggest no or slightly prograde rotation for the population of halo RR Lyraes in the Milky Way.

Globular cluster distance moduli from theKband period-luminosity relation for RR lyraes

Abstract Having analysed the published observations in the K band (2.2 μm) for 173 RR Lyraes in nine galactic globular clusters, we derived the relation (MK ) = -2.338 log PF - 0.88. This relation corresponds to the LMC distance modulus modoV (RR) = 18.23 ± 0.04. Using the (Mk) - log Pf relation, we obtained distance moduli for the nine globulars; they are in good agreement with Kukarkin's (1974) system of distance moduli, but differ systematically (on average, by +0m14) from distance moduli in the system by Harris (1996). We critically discuss some recently published values of the LMC distance modulus.

Period-luminosity and period-luminosity-colour relations for Mira variables at maximum light

In this paper we confirm the existence of period-luminosity (PL) and period-luminosity-colour (PLC) relations at maximum light for O and C Mira variables in the LMC. We demonstrate that in the J and H bands the maximum light PL relations have a significantly smaller dispersion than their counterparts at mean light, while the K band and bolometric PL relations have a dispersion comparable to that at mean light. In the J, H and K bands the fitted PL relations for the O Miras are found to have smaller dispersion than those for the C Miras, at both mean and maximum light, while the converse is true for the relations based on bolometric magnitudes. The inclusion of a non-zero log period term is found to be highly significant in all cases except that of the C Miras in the J band, for which the data are found to be consistent with having constant absolute magnitude. This suggests the possibility of employing C Miras as standard candles. We suggest both a theoretical justification for the existence of Mira PL relations at maximum light and a possible explanation of why these relations should have a smaller dispersion than at mean light. The existence of such maximum light relations offers the possibility of extending the range and improving the accuracy of the Mira distance scale to Galactic globular clusters and to other galaxies.

JHK photometry for 54 southern Milky Way Cepheids

JHK photometry is presented for 54 distant southern Milky Way Cepheids, 9 of which were discovered in a recent survey of Crux and Centaurus. Color excesses obtained from the H-K period-color relation show excellent agreement with those obtained from BVI photometry. Distances are computed using the K band period-luminosity relation. Five of the newly discovered Cepheids and one of those previously known are particularly well positioned for a determination of R 0 , the distance to the galactic center