arXiv subjects

Harinder P. Singh

Publications and source records attributed to Harinder P. Singh.

At least 55 records · Page 3Linked to original sources

arXiv2016

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 ($3.6~\&~4.5μ\mathrm{m}$) 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 $Δμ=0.49\pm0.02$~mag between the two clouds is estimated using multi-band PL relations for the first-overtone mode Cepheids in the SMC and LMC.

astro-ph.GA↗

arXiv2016

Large Magellanic Cloud Near-Infrared Synoptic Survey. III. A Statistical Study of Non-Linearity in the Leavitt Laws

We present a detailed statistical analysis of possible non-linearities in the Period-Luminosity (P-L), Period-Wesenheit (P-W) and Period-Color (P-C) relations for Cepheid variables in the LMC at optical ($VI$) and near-infrared ($JHK_{s}$) wavelengths. We test for the presence of possible non-linearities and determine their statistical significance by applying a variety of robust statistical tests ($F$-test, Random-Walk, Testimator and the Davies test) to optical data from OGLE III and near-infrared data from LMCNISS. For fundamental-mode Cepheids, we find that the optical P-L, P-W and P-C relations are non-linear at 10 days. The near-infrared P-L and the $W^H_{V,I}$ relations are non-linear around 18 days; this break is attributed to a distinct variation in mean Fourier amplitude parameters near this period for longer wavelengths as compared to optical bands. The near-infrared P-W relations are also non-linear except for the $W_{H,K_s}$ relation. For first-overtone mode Cepheids, a significant change in the slope of P-L, P-W and P-C relations is found around 2.5 days only at optical wavelengths. We determine a global slope of $\textrm{-}3.212\pm0.013$ for the $W^H_{V,I}$ relation by combining our LMC data with observations of Cepheids in Supernovae host galaxies \citep{riess11}. We find this slope to be consistent with the corresponding LMC relation at short periods, and significantly different to the long-period value. We do not find any significant difference in the slope of the global-fit solution using a linear or non-linear LMC P-L relation as calibrator, but the linear version provides a $2\times$ better constraint on the slope and metallicity coefficient.

astro-ph.GA↗

arXiv2015

New atmospheric parameters and spectral interpolator for the MILES cool stars

Context: The full spectrum fitting of stellar spectra against a library of empirical spectra is a well-established approach to measure the atmospheric parameters of FGK stars with a high internal consistency. Extending it towards cooler stars still remains a challenge. Aims: We address this question by improving the interpolator of the MILES (Medium-resolution INT Library of Empirical Spectra) library in the low effective temperature regime (Tefff < 4800 K), and we refine the determination of the parameters of the cool MILES stars. Methods: We use the ULySS package to determine the atmospheric parameters (Teff, logg and [Fe/H]), and measure the biases of the results with respect to our updated compilation of parameters calibrated against theoretical spectra. After correcting some systematic effects, we compute a new interpolator that we finally use to redetermine the atmospheric parameters homogeneously and assess the biases. Results: Based on an updated literature compilation, we determine Teff in a more accurate and unbiased manner compared to those determined with the original interpolator. The validity range is extended downwards to about Teff = 2900 K compared to 3500 K previously. The mean residual biases on Teff, logg, and [Fe/H], with respect to the literature compilation for the coolest stars (Teff <= 3800 K) computed using the new interpolator, are -15 K, -0.02 dex, and 0.02 dex respectively. The corresponding estimations of the external precision are 63 K, 0.23 dex, and 0.15 dex respectively. For the stars with Teff in the range 3800 - 4200 K, the determinations of Teff and [Fe/H] have been slightly improved. At higher temperatures, the new interpolator is comparable to the original one. The new version of the interpolator is publicly available.

astro-ph.SR↗

arXiv2015

Updated 24 $μ\mathrm{m}$ Period-Luminosity Relation Derived from Galactic Cepheids

In this work, we updated the catalog of Galactic Cepheids with $24μ\mathrm{m}$ photometry by cross-matching the positions of known Galactic Cepheids to the recently released MIPSGAL point source catalog. We have added 36 new sources featuring MIPSGAL photometry in our analysis, thus increasing the existing sample to 65. Six different sources of compiled Cepheid distances were used to establish a $24μ\mathrm{m}$ period-luminosity (P-L) relation. Our recommended $24μ\mathrm{m}$ P-L relation is $M_{24μ\mathrm{m}}=-3.18(\pm0.10)\log P - 2.46(\pm0.10)$, with an estimated intrinsic dispersion of 0.20 mag, and is derived from 58 Cepheids exhibiting distances based on a calibrated Wesenheit function. The slopes of the P-L relations were steepest when tied solely to the 10 Cepheids exhibiting trigonometric parallaxes from the Hubble Space Telescope and Hipparcos. Statistical tests suggest that these P-L relations are significantly different from those associated with other methods of distance determination, and simulations indicate that difference may arise from the small sample size.

astro-ph.SR↗

arXiv2015

Large Magellanic Cloud Near-Infrared Synoptic Survey. II. The Wesenheit relations and their application to the Distance scale

We present new near-infrared Cepheid Period-Wesenheit relations in the LMC using time-series observations from the Large Magellanic Cloud Near-Infrared Synoptic Survey. We also derive optical$+$near-infrared P-W relations using $V$ and $I$~magnitudes from OGLE-III. We employ our new $JHK_s$ data to determine an independent distance to the LMC of $μ_{\rm LMC} = 18.47\pm0.07 {\textit{(statistical)}}$~mag, using an absolute calibration of the Galactic relations based on several distance determination methods and accounting for the intrinsic scatter of each technique. We also derive new near-infrared Period-Luminosity and Wesenheit relations for Cepheids in M31 using observations from the PHAT survey. We use the absolute calibrations of the Galactic and LMC $W_{J,H}$ relations to determine the distance modulus of M31, $μ_{\rm M31} = 24.46\pm0.20$~mag. We apply a simultaneous fit to Cepheids in several Local Group galaxies covering a range of metallicities ($7.7<12+\log[O/H]<8.6$~dex) to determine a global slope of -$3.244\pm0.016$~mag/dex for the $W_{J,K_s}$ relation and obtain robust distance estimates. Our distances are in good agreement with recent TRGB based distance estimates and we do not find any evidence for a metallicity dependence in the near-infrared P-W relations.

astro-ph.GA↗

arXiv2015

Period-Luminosity Relations Derived From the OGLE-III Fundamental Mode Cepheids II: The Small Magellanic Cloud Cepheids

In this paper we present multi-band period-luminosity (P-L) relations for fundamental mode Cepheids in the SMC. The optical VI-band mean magnitudes for these SMC Cepheids were taken from the third phase of the Optical Gravitational Lensing Experiment (OGLE-III) catalog. We also matched the OGLE-III SMC Cepheids to 2MASS and SAGE-SMC catalog to derive mean magnitudes in the JHK-bands and the four {\it Spitzer} IRAC bands, respectively. All photometry was corrected for extinction by adopting the Zaritsky's extinction map. Cepheids with periods smaller than $\sim2.5$ days were removed from the sample. In addition to the extinction corrected P-L relations in nine filters from optical to infrared, we also derived the extinction-free Wesenheit function for these Cepheids. We tested the nonlinearity of these SMC P-L relations (except the $8.0μ\mathrm{m}$-band P-L relation) at 10 days: none of the P-L relations show statistically significant evidence of nonlinearity. When compared to the P-L relations in the LMC, the t-test results revealed that there is a difference between the SMC/LMC P-L slopes only in the V- and J-band. Further, we found excellent agreement between the SMC/LMC Wesenheit P-L slope. The difference in LMC and SMC Period-Wesenheit relation LMC and SMC zero points was found to be $Δμ=0.483\pm0.015$ mag. This amounts to a difference in distance modulus between the LMC and SMC.

astro-ph.SR↗

arXiv2015

The evolution of disc galaxies with and without classical bulges since z~1

Establishing the relative role of internally and externally driven mechanisms responsible for disc and bulge growth is essential to understand the evolution of disc galaxies. In this context, we have studied the physical properties of disc galaxies without classical bulges in comparison to those with classical bulges since z~0.9. Using images from the Hubble Space Telescope and Sloan Digital Sky Survey, we have computed both parametric and non-parametric measures, and examined the evolution in size, concentration, stellar mass, effective stellar mass density and asymmetry. We find that both disc galaxies with and without classical bulges have gained more than 50% of their present stellar mass over the last ~8 Gyrs. Also, the increase in disc size is found to be peripheral. While the average total (Petrosian) radius almost doubles from z~0.9 to z~0, the average effective radius undergoes a marginal increase in comparison. Additionally, increase in the density of the inner region is evident through the evolution of both concentration and effective stellar mass density. We find that the asymmetry index falls from higher to lower redshifts, but this is more pronounced for the bulgeless disc sample. Also, asymmetry correlates with the global effective radius, and concentration correlates with the global Sersic index, but better so for higher redshifts only. The substantial increase in mass and size indicates that accretion of external material has been a dominant mode of galaxy growth, where the circumgalactic environment plays a significant role.

astro-ph.GA↗

arXiv2015

Reliability of UPO based control strategies in biological systems

Presence of recurrent and statistically significant unstable periodic orbits (UPOs) in time series obtained from biological systems are now routinely used as evidence for low dimensional chaos . Extracting accurate dynamical information from the detected UPO trajectories are vital for successful control strategies that either aim to stabilize the system near the fixed point or steer the system away from the periodic orbits. A hybrid UPO detection method from return maps that combines topological recurrence criterion, matrix fit algorithm and stringent criterion for fixed point location gives accurate and statistically significant UPOs even in the presence of significant noise. Geometry of the return map, frequency of UPOs visiting the same trajectory, length of the data set, strength of the noise and degree of nonstationarity affect the efficacy of the proposed method. Results suggest that establishing determinism from unambiguous UPO detection is often possible in short data sets with significant noise, but derived dynamical properties are rarely accurate and adequate for controlling the dynamics around these UPOs. A repeat chaos control experiment on epileptic hippocampal slices through more stringent control strategy and adaptive UPO tracking is reinterpreted in this context through simulation of similar control experiments on an analogous but stochastic computer model of epileptic brain slices. Reproduction of equivalent results suggests that far more stringent criteria are needed for linking apparent success of control in such experiments with possible determinism in the underlying dynamics.

nlin.AO↗

arXiv2015

Morphology and metallicity of the Small Magellanic Cloud using RRab stars

We present a study of three-dimensional structure of the Small Magellanic Cloud (SMC). The $V$- and $I$-band light curves of the fundamental mode RR Lyrae stars (RRab) obtained by the Optical Gravitational Lensing Experiment (OGLE)-III project were utilized in order to comprehend the SMC structure. The $[Fe/H]-P-ϕ_{31}$ relation of \citet{jurc96} is exploited to obtain the metallicities. From the three-dimensional RRab distance distributions, northeast (NE) arm and main body of the galaxy is identified. Combining metallicities with spatial distribution of these tracers, no radial metallicity gradient in the SMC has been detected. Dividing the entire sample into three parts: northeastern (NE), central and southwestern (SW), we find that the central part has a significantly larger line of sight depth as compared to rest of the parts, indicating that the SMC may have a bulge. Results obtained from the $I$-band data seem to be reliable and were further substantiated using the \citet{smol05} relation. Distribution of SMC RRab stars were modeled as a tri-axial ellipsoid. Errors in structural parameters of the SMC ellipsoid were obtained from Monte Carlo simulations. We estimated the axes ratios of the galaxy as $1.00\pm 0.000:1.310\pm 0.029:8.269\pm0.934$, the inclination of the longest axis with line of sight $i = 2^{\circ}.265\pm 0^{\circ}.784$, and the position angle of the line of nodes $θ_{\text{lon}}=74^{\circ}.307\pm 0^{\circ}.509$ from the variance weighted $I$-band determinations.

astro-ph.SR↗

arXiv2014

On the Variation of Fourier Parameters for Galactic and LMC Cepheids at Optical, Near-Infrared and Mid-Infrared Wavelengths

We present a light curve analysis of fundamental-mode Galactic and Large Magellanic Cloud (LMC) Cepheids based on the Fourier decomposition technique. We have compiled light curve data for Galactic and LMC Cepheids in optical ({\it VI}), near-infrared ({\it JHK}$_s$) and mid-infrared (3.6 $\&$ 4.5-$μ$m) bands from the literature and determined the variation of their Fourier parameters as a function of period and wavelength. We observed a decrease in Fourier amplitude parameters and an increase in Fourier phase parameters with increasing wavelengths at a given period. We also found a decrease in the skewness and acuteness parameters as a function of wavelength at a fixed period. We applied a binning method to analyze the progression of the mean Fourier parameters with period and wavelength. We found that for periods longer than about 20 days, the values of the Fourier amplitude parameters increase sharply for shorter wavelengths as compared to wavelengths longer than the $J$-band. We observed the variation of the Hertzsprung progression with wavelength. The central period of the Hertzsprung progression was found to increase with wavelength in the case of the Fourier amplitude parameters and decrease with increasing wavelength in the case of phase parameters. We also observed a small variation of the central period of the progression between the Galaxy and LMC, presumably related to metallicity effects. These results will provide useful constraints for stellar pulsation codes that incorporate stellar atmosphere models to produce Cepheid light curves in various bands.

astro-ph.SR↗

arXiv2014

Empirical Period-Color and Amplitude-Color Relations for Classical Cepheids and RR Lyrae Variables

We analyze Galactic, Large Magellanic Cloud and Small Magellanic Cloud Cepheids and RR Lyrae variables in terms of period-color (PC) and amplitude-color (AC) diagrams at the phases of maximum and minimum light. We compiled Galactic Cepheids $V$- and $I$-band data from the literature. We make use of optical bands light curve data from OGLE-III survey for Cepheids and RR Lyrae variables in the Magellanic Clouds. We apply the $F$-statistical test to check the significance of any variation in the slope of PC and AC relations for Cepheid variables. The PC relation at maximum light for Galactic Cepheids with periods longer than about 7 days is shallow and the corresponding AC relation is flat for the entire period range. For the fundamental mode Cepheids in the Magellanic Clouds, we find significant breaks in the PC and AC relations at both maximum and minimum light for periods around 10 days. The PC relation at maximum light for the Magellanic Clouds is flat for Cepheids with periods greater than 10 days. First overtone Cepheids with periods less than 2.5 days have a shallow PC relation at minimum light. For fundamental mode RR Lyraes, we confirm earlier work supporting a flat PC relation at minimum light and a significant relation between amplitude and color at maximum light. We find that no such relations exist for first overtone RR Lyrae stars. These findings are in agreement with stellar photosphere/hydrogen ionization front interaction considerations. These nonlinearities can provide strong constraints for models of stellar pulsation and evolution.

astro-ph.SR↗

arXiv2013

Chemical and structural analysis of the Large Magellanic Cloud using the fundamental mode RR Lyrae stars

We present a careful and detailed light curve analysis of publicly available $I$-band data on fundamental mode RR Lyrae (RRab) stars of the Large Magellanic Cloud (LMC) obtained by the Optical Gravitational Lensing Experiment (OGLE) phase-III project. Using the Fourier parameters of $13,095$ RRab stars, metallicities and absolute magnitudes of individual stars are obtained. The representation of stars on the $P-ϕ_{31}^{V}$ plane shows the existence of three significant metallicity groups with mean metallicities as $-1.20 \pm 0.12$ dex, $-1.57 \pm 0.10$ dex and $-1.89 \pm 0.09$ dex. The corresponding absolute magnitudes of these three groups are obtained as $0.70\pm 0.08$ mag, $0.59 \pm 0.06$ mag and $0.49 \pm 0.08$ mag, respectively. Distribution of these three groups as a function of vertical $|z|$ distance indicates that the formation of the LMC disk predates the formation of the inner halo. Issue of the existence of a metallicity gradient as a function of galactocentric distances has also been addressed. Approximating the structure of the LMC disk as a triaxial ellipsoid, the inclination angle ($i$) relative to the plane of the sky and the position angle of the line of nodes ($θ_{lon}$) were estimated as $24^{\circ}.20$ and $176^{\circ}.01$, respectively. The axes ratios and the eccentricity were also determined using the principal axes transformation method.

astro-ph.SR↗

arXiv2013

Visibility graph analysis of solar wind velocity

We analyze in situ measurements of solar wind velocity obtained by Advanced Composition Explorer (ACE) spacecraft and Helios spacecraft during the years 1998-2012 and 1975-1983 respectively. The data belong to mainly solar cycle 23 (1996-2008) and solar cycle 21 (1976-1986) respectively. We use Directed Horizontal Visibility graph (DHVg) algorithm and estimate a graph functional, namely, the degree distance (D) as the Kullback-Leibler divergence (KLD) argument to understand time irreversibility of solar wind time series. We estimate this degree distance irreversibility parameter for these time series at different phases of solar activity cycle. Irreversibility parameter is first established for known dynamical data and then applied for solar wind velocity time series. It is observed that irreversibility in solar wind velocity fluctuations show similar behaviour at 0.3 AU (Helios data) and 1 AU (ACE data). Moreover it changes over the different phases of solar activity cycle.

astro-ph.SR↗

arXiv2011

Hysteresis in a Solar Activity Cycle

We analyze in situ measurements of solar wind velocity obtained by the Advanced Composition Explorer (ACE) spacecraft during the solar activity cycle 23. We calculated a robust complexity measure, the permutation entropy (S) of solar wind time series at different phases of a solar activity cycle. The permutation entropy measure is first tested on the known dynamical data before its application to solar wind time series. It is observed that complexity of solar wind velocity fluctuations at 1 AU shows hysteresis phenomenon while following the ascending and descending phases of the activity cycle. This indicates the presence of multistability in the dynamics governing the solar wind velocity over a solar activity cycle.

astro-ph.SR↗

arXiv2011

Symbolic analysis of slow solar wind data using rank order statistics

We analyze time series data of the fluctuations of slow solar wind velocity using rank order statistics. We selected a total of 18 datasets measured by the Helios spacecraft at a distance of 0.32 AU from the sun in the inner heliosphere. The datasets correspond to the years 1975-1982 and cover the end of the solar activity cycle 20 to the middle of the activity cycle 21. We first apply rank order statistics to time series from known nonlinear systems and then extend the analysis to the solar wind data. We find that the underlying dynamics governing the solar wind velocity remains almost unchanged during an activity cycle. However, during a solar activity cycle the fluctuations in the slow solar wind time series increase just before the maximum of the activity cycle

astro-ph.SR↗

arXiv2010

Physical parameters of 62 eclipsing binary stars using the ASAS-3 data$-$I

We present a detailed light curve analysis of publicly available V band observations of 62 binary stars, mostly contact binaries, obtained by the All Sky Automated Survey (ASAS)-3 project between 2000 and 2009. Eclipsing binaries are important astronomical targets for determining the physical parameters of component stars from the geometry. They provide an independent direct method of measuring the radii of stars. We improved the ASAS determined periods, ephemeris and obtained the Fourier parameters from the phased light curves of these 62 stars. These Fourier parameters were used for preliminary classification of the stars in our sample. The phased light curves were then analysed with the aid of the Wilson-Devinney light curve modelling technique in order to obtain various geometrical and physical parameters of these binaries. The spectroscopic mass ratios as determined from the the radial velocity measurements available in the literature were used as one of the inputs to the light curve modelling. Thus reliable estimations of parameters of these binaries were obtained with combined photometric and spectroscopic data and error estimates were made using the heuristic scan method.

astro-ph.SR↗

arXiv2010

Coude-feed stellar spectral library - atmospheric parameters

Context: Empirical libraries of stellar spectra play an important role in different fields. For example, they are used as reference for the automatic determination of atmospheric parameters, or for building synthetic stellar populations to study galaxies. The CFLIB (Coude-feed library, Indo-US) database is at present one of the most complete libraries, in terms of its coverage of the atmospheric parameters space (Teff, log g and [Fe/H]) and wavelength coverage 3460 - 9464 A at a resolution of 1 A FWHM. Although the atmospheric parameters of most of the stars were determined from detailed analyses of high-resolution spectra, for nearly 300 of the 1273 stars of the library at least one of the three parameters is missing. For the others, the measurements, compiled from the literature, are inhomogeneous. Aims: In this paper, we re-determine the atmospheric parameters, directly using the CFLIB spectra, and compare them to the previous studies. Methods: We use the ULySS program to derive the atmospheric parameters, using the ELODIE library as a reference. Results: Based on comparisons with several previous studies we conclude that our determinations are unbiased. For the 958 F,G, and K type stars the precision on Teff, log g, and [Fe/H] is respectively 43 K, 0.13 dex and 0.05 dex. For the 53 M stars they are 82 K, 0.22 dex and 0.28 dex. And, for the 260 OBA type stars the relative precision on Teff is 5.1%, and on log g, and [Fe/H] the precision is respectively 0.19 dex and 0.16 dex. These parameters will be used to re-calibrate the CFLIB fluxes and to produce synthetic spectra of stellar populations.

astro-ph.SR↗

arXiv2010

A CCD photometric study of the newly discovered contact binary ASAS 134738+0410.1

We present a CCD photometric study of the star with ASAS ID 134738 + 0410.1 using V band observations obtained from the $IUCAA$ Girawali Observatory (IGO) 2-metre telescope, India. The star was selected from the $δ$ Scuti database of All Sky Automated Survey (ASAS) (Pojmanski 2002). Our analysis reveals that the star is not a $δ$ Scuti variable but is in fact a W UMa type contact binary with an orbital period of 0.2853067 day. Two new times of primary and secondary minima were determined from the observed data. A preliminary solution obtained using the Wilson-Devinney light curve modelling technique indicates that the star is more likely a partially-eclipsing W UMa type contact binary. However, the determination of actual subtype of this binary is quite impossible from the photometry alone, as the observed light curve can fitted for both A- and W-type solutions. The exact classification of this binary needs to be determined from high resolution spectroscopy.

astro-ph.SR↗