2010 (IPP)

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Associated spectral and temporal state transition of the bright ULX NGC 1313 X-1
(2010-05-21) Dewangan, Gulab Chand; et al.
Stellar mass black hole X-ray binaries exhibit X-ray spectral states which also have distinct and characteristic temporal properties. These states are believed to correspond to diﬀerent accretion disc geometries. We present analysis of two XMM-Newton observations of the Ultra-Luminous X-ray source (ULX) NGC 1313 X-1, which reveal that the system was in two diﬀerent spectral states. While spectral variations have been observed in this source before, this data provides clear evidence that the spectral states also have distinct temporal properties. With a count rate of ~ 1.5 counts/s and a fractional variability amplitude of ~ 15%, the ULX was in a high ﬂux and strongly variable state in March 2006. In October 2006, the count rate of the ULX had reduced by a factor of ~ 2 and the spectral shape was distinctly diﬀerent with the presence of a soft component. No strong variability was detected during this low ﬂux state with an upper limit on the amplitude < 3%. Moreover, the spectral properties of the two states implies that the accretion disc geometry was diﬀerent for them. The low ﬂux state is consistent with a model where a standard accretion disc is truncated at a ra- dius of ~ 17 Schwarzschild radius around a ~ 200M⊙ black hole. The inner hot region Comptonizes photons from the outer disc to give the primary spectral component. The spectrum of the high ﬂux state is not compatible with such a geometry. Instead, it is consistent with a model where a hot corona covers a cold accretion disc and Comptonizes the disc photons. The variability as a function of energy is also shown to be consistent with the corona model. Despite these broad analogies with Galactic black hole systems, the spectral nature of the ULX is distinct in having a lower temperature (~ 2 keV) of the hot Comptonizing plasma and higher optical depth (~ 15) than what is observed for the Galactic ones.
Bar fraction in lenticular galaxies: Dependence on luminosity and environment
(2010-10-15) Barway, Sudhanshu; Wadadekar, Yogesh; Kembhavi, A.K.
We present a study of bars in lenticular galaxies based on a sample of 371 galaxies from the SDSS-DR 7 and 2MASS in optical and near-infrared bands, respectively. We found a bar in 15% of the lenticular galaxies in our sample, which is consistent with recent stud- ies. The barred galaxy fraction shows a luminosity dependence, with faint lenticular galaxies (MK > −24.5, total absolute magnitude in K band) having a larger fraction of bars than bright lenticular galaxies (MK < −24.5). A similar trend is seen when Mr = −21.5, the total absolute magnitude in SDSS r band is used to divide the sample into faint and bright lenticular galaxies.We ﬁnd that faint galaxies in clusters show a higher bar fraction than their counterparts in the ﬁeld. This suggests that the formation of bars in lenticular galaxies not only depends on the total luminosity of galaxy but also on the environment of the host galaxy.
CCD photometric study of the late type contact binary EK comae berenices
(2010-04-26) Deb, Sukanta; Singh, Harinder P.; Seshadri, T. R.; et al.
We present CCD photometric observations of the W UMa type contact binary EK Comae Berenices using the 2 metre telescope of IUCAA Girawali Observatory, India. The star was classiﬁed as a W UMa type binary of subtype-W by Samec et al. [20]. The new V band photometric observations of the star reveal that shape of the light curve has changed signiﬁcantly from the one observed by Samec et al. [20]. A detailed analysis of the light curve obtained from the high-precision CCD photometric observations of the star indicates that EK Comae Berenices is not a W-type but an A-type totally eclipsing W UMa contact binary. The photometric mass ratio is determined to be 0.349 ± 0.005. A temperature diﬀerence of ∆T = 141 ± 10 K between the components and an orbital inclination of i[°] = 89.800 ± 0.075 were obtained for the binary system. Absolute values of masses, radii and luminosities are estimated by means of the standard mass-luminosity relation for zero age main-sequence stars. The star shows O’Connell eﬀect, asymmetries in the light curve shape around the primary and secondary maximum. The observed O’Connell eﬀect is explained by the presence of a hot spot on the primary component.
Charged black holes in vaidya backgrounds: Hawkings's radiation
(2010-12-25) Ibohal, Ng.; Kapil, L.
In this paper we propose a class of embedded solutions of Einstein's field equations describing non-rotating Reissner-Nordstrom-Vaidya and rotating Kerr-Newman-Vaidya black holes. The Reissner-Nordstrom-Vaidya is obtained by embedding Reissner-Nordstrom solution into non-rotating Vaidya. Similarly, we also find the Kerr-Newman-Vaidya black hole, when Kerr-Newman embeds into the rotating Vaidya solution. The Reissner-Nordstrom-Vaidya solution is type D whereas Kerr-Newman-Vaidya metric is algebraically special type II of Petrov classification of space-time. These embedded solutions can be expressed in Kerr-Schild ansatze on different backgrounds. The energy momentum tensors for both non-rotating as well as rotating embedded solutions satisfy the energy conservation equations which show that they are solutions of Einstein's field equations. The surface gravity, area, temperature and entropy are also presented for each embedded black hole. It is observed that the area of the embedded black holes is greater than the sum of the areas of the individual ones. By considering the charge to be a function of radial coordinate it is shown that there is a change in the masses of the variable charged black holes. If such radiation continues, the mass of the black hole will evaporate completely thereby forming `instantaneous' charged black holes and creating embedded `negative mass naked singularities' describing the possible life style of radiating embedded black holes during their continuous radiation processes.
Coherent versus coincidence detection of gravitational wave signals from compact inspiraling binaries
(2010-03-30) Dhurandhar, Sanjeev; Mukhopadhyay, Himan; Tagoshi, H.; et al.
We compare two multi-detector detection strategies, namely, the coincidence and the coherent, for the detection of spinless inspiraling compact binary gravitational wave (GW) signals. The coincident strategy treats the detectors as if they are isolated - com- pares individual detector statistics with their respective thresholds while the coherent strategy combines the detector network data phase coherently to obtain a single detection statistic which is then compared with a single threshold. In the case of geographically separated detectors, we also consider an enhanced coincidence strategy because the usual (naive) coincidence strategy yields poor results for misaligned detectors. For simplicity, we consider detector pairs having the same power spectral density of noise, as that of initial LIGO and also assume the noise to be stationary and Gaussian. We compare the performances of the methods by plotting the receiver operating characteristic (ROC) for the two strategies. A single astrophysical source as well as a distribution of sources is considered. We ﬁnd that the coherent strategy performs better than the two coincident strategies under the assumptions of stationary Gaussian detector noise.
Cosmic ray driven outflows from high redshift galaxies
(2010-01-10) Samui, Saumyadip; Subramanian, Kandaswamy; Srianand, R.
We study winds in high redshift galaxies driven by a relativistic cosmic ray (proton) component in addition to the hot thermal gas component. Cosmic rays (CRs) are likely to be efﬁciently generated in supernova(SNe)shocks inside galaxies. We obtain solutions of such CR driven free winds in a gravitational potential of the Navarro-Frenk-White (NFW) form, relevant to galaxies. Cosmic rays naturally provide the extra energy and/or momentum input to the system, needed for a transonic wind solution in a gas with adiabatic index = 5=3.We show that cosmic rays can effectively drive winds even when the thermal energy of the gas is lost due to radiative cooling. These wind solutions predict an asymptotic wind speed closely related to the circular velocity of the galaxy. Furthermore, the mass outﬂow rate per unit star formation rate ( w) is predicted to be ~ 0:2 0:5 for massive galaxies, with masses M ~ 1011 1012M .We show w to be inversely proportional to the square of the circular velocity. Magnetic ﬁelds at the G levels are also required in these galaxies to have a signiﬁcant mass loss. A large w for small mass galaxies implies that cosmic ray driven outﬂows could provide a strong negative feedback to the star formation in dwarf galaxies. Further, our results will also have important implications to the metal enrichment of the intergalactic medium. These conclusions are applicable to the class of free wind models where the source region is conﬁned to be within the sonic point.
Coude-feed stellar spectral library - atmospheric parameters
(2010-09-09) Wu, Yue; et al.; Singh, Harinder P.; Prugniel, Philippe
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 (Coud´e-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.
Detection of 21-cm, H2 and Deuterium absorption at z>3 along the line-of-sight to J1337+3152
(2010-02-24) Srianand, R.; Gupta, Neeraj; Petitjean, Patrick; et al.
We report the detection of 21-cm and molecular hydrogen absorption lines in the same damped Lyman-α system (with log N(H i)=21.36±0.10) at zabs=3.17447 towards SDSS J133724.69+315254.55 (zem ∼3.174). We estimate the spin temperature of the gas to be, TS = 600+222−159 K, intermediate between the expected values for cold and warm neutral media. This suggests that the H i absorption originates from a mixture of diﬀerent phases. The total molecular fraction is low, fH2=10−7, and H2 rotational level populations are not in equilibrium. The average abundance of the α- elements is, [S/H]=−1.45 ± 0.22. Nitrogen and iron are found underabundant with respect to α-elements by ∼1.0 dex and ∼0.5 dex respectively. Using photoionization models we conclude that the gas, of mean density, nH ∼2 cm−3, is located more than 270 kpc away from the QSO. While the position of 21-cm absorption line coincides with the H2 velocity proﬁle, its centroid is shifted by ∼2.7±1.0 km s−1 with respect to the redshift measured from the H2 lines. However, the position of the strongest metal absorption component matches the position of the 21-cm absorption line within 0.5 km s−1. From this, we constrain the variation of the combination of fundamental constants x = α2Gp/µ, ∆x/x = −(1.7±1.7)×10−6. This system is unique as we can at the same time have an independent constrain on µ using H2 lines. However, as the H2 column density is low, only Werner band absorption lines are seen and, unfortunately, the range of sensitivity coeﬃcients is too narrow to provide a stringent constraint: ∆µ/µ ≤ 4.0 × 10−4. The Ultraviolet and Visual Echelle Spectrograph (UVES) spectrum reveals another DLA at zabs= 3.16768 with log N(H i) = 20.41±0.15 and low metallicity, [Si/H] = −2.68 ± 0.11, in which [O/C] ∼ 0.18 ± 0.18 and [O/Si] ∼ 0. This shows that even in the very early stages of chemical evolution, the carbon or silicon to oxygen ratios can be close to solar. Using Voigt proﬁle ﬁtting we derive log(N(D i)/N(H i)) = −(4.93 ± 0.15) in this system. This is a factor of two smaller than the value expected from the best ﬁtted value of Ωb from theWilkinson Microwave Anisotropy Probe (WMAP) 5 year data. This conﬁrms the presence of astration of deuterium even at very low metallicity.
Evolution of shocks and turbulence in major cluster mergers
(2010-12-14) Paul, Surajit; Iapichino, L.; Miniati, F.; et al.
We performed a set of cosmological simulations of major mergers in galaxy clusters, in order to study the evolution of merger shocks and the subsequent injection of turbulence in the post-shock region and in the intra-cluster medium (ICM). The computations have been performed with the grid-based, adaptive mesh reﬁnement (AMR) hydrodynamical code Enzo, using a reﬁnement criterion especially designed for reﬁning turbulent ﬂows in the vicinity of shocks. When a major merger event occurs, a substantial amount of turbulence energy is injected in the ICM of the newly formed cluster. Our simulations show that the shock launched after a major merger develops an ellipsoidal shape and gets broken by the interaction with the ﬁlamentary cosmic web around the merging cluster. The size of the post-shock region along the direction of shock propagation is of the order of 300 kpc h−¹, and the turbulent velocity dispersion in this region is larger than 100 km s−¹. We performed a scaling analysis of the turbulence energy within our cluster sample. The best ﬁt for the scaling of the turbulence energy with the cluster mass is consistent with M⁵/³, which is also the scaling law for the thermal energy in the self-similar cluster model. This clearly indicates the close relation between virialization and injection of turbulence in the cluster evolution. As for the turbulence in the cluster core, we found that within 2 Gyr after the major merger (the timescale for the shock propagation in the ICM), the ratio of the turbulent to total pressure is larger than 10%, and after about 4 Gyr it is still larger than 5%, a typical value for nearly relaxed clusters. Turbulence at the cluster center is thus sustained for several Gigayears, which is substantially longer than typically assumed in the turbulent re-accelerationmodels, invoked for explaining the statistics of observed radio halos. Striking similarities in the morphology and other physical parameters between our simulations and the ‘symmetrical radio relics’ found at the periphery of the merging cluster Abell 3376 are ﬁnally discussed. In particular, the interaction between the merger shock and the ﬁlaments surrounding the cluster could explain the presence of ‘notch-like’ features at the edges of the double relics.
GMRT mini-survey to search for 21-cm absorption in quasar-galaxy pairs at z~0.1
(2010-07-05) Gupta, N.; et al.; Srianand, R.
We present the results from our 21-cm absorption survey of a sample of 5 quasar-galaxy pairs (QGPs), with the redshift of the galaxies in the range 0.03≤ zg ≤ 0.18, selected from the Sloan Digital Sky Survey (SDSS). The H i 21-cm absorption was searched towards the 9 sight lines with impact parameters ranging from ∼10 to ∼55 kpc using Giant Metrewave Radio Telescope (GMRT). 21-cm absorption was detected only in one case i.e. towards the Quasar (zq = 2.625SDSS J124157.54+633241.6) − galaxy (zg = 0.143 SDSS J124157.26+633237.6) pair with the impact parameter ∼11 kpc. The quasar sight line in this case pierces through the stellar disk of a galaxy having near solar metallicity (i.e (O/H)+12 = 8.7) and star formation rate uncorrected for dust attenuation of 0.1M⊙ yr−1. The quasar spectrum reddened by the foreground galaxy is well ﬁtted with the Milky Way extinction curve (with an AV of 0.44) and the estimated H i column density is similar to the value obtained from 21-cm absorption assuming spin temperature (TS) of 100K. In the remaining cases, our GMRT spectra provide upper limit on N(H i) in the range, (1017 −1018)×TS cm−2. Combining our sample with the z ≤ 0.1 data available in the literature, we ﬁnd the detectability of 21-cm absorption with integrated optical depth greater than 0.1 kms−1 to be 50% for the impact parameter less than 20 kpc. Using the surface brightness proﬁles and well established relationship between the optical size and extent of the H i disk known for nearby galaxies, we conclude that in most of the cases of 21-cm absorption non-detection, the sight lines may not be passing through the H i gas (1σ column density of few times 1019 cm−2). We also ﬁnd that in comparison to the absorption systems associated with these QGPs, z < 1 DLAs with 21-cm absorption detections have lower Ca ii equivalent widths despite having higher 21-cm optical depths and smaller impact parameters. This suggests that the current sample of DLAs may be a biased population that avoids sight lines through dusty star-forming galaxies. A systematic survey of QGPs over a wider redshift range using a large sample is needed to conﬁrm these ﬁndings and understand the nature of 21-cm absorbers.
Group theoretic approach to detecting gravitational waves from asymmetric rotating neutron stars
(2010-10-12) Dhurandhar, Sanjeev; Krishnan, B.
The era of advanced ground based interferometric detectors of gravitational waves (GW) has arrived. These detectors are expected to go line in six years or so from now and which will have requisite sensitivity for detecting and observing astrophysical gravitational wave sources. In this article we will focus on a speciﬁc GW source, the GWs emitted by an isolated rotating neutron star/pulsar, and describe a novel approach to address this highly com- putationally intensive problem. We will describe how the symmetries in the model can be potentially used to reduce the computational effort.
HD molecules at high redshift: The absorption system at z=2.3377 towards Q 1232+082
(2010-02-10) Srianand, R.
Interstellar dust models towards some IUE stars
(2010-11-24) Katyal, Nisha; Gupta, Ranjan; Vaidya, D.B.
We present a study of interstellar extinction towards certain directions in our galaxy deﬁned by about 59 stars which were observed by the IUE satellite. The observed UV extinction curves have been modeled by making light scattering calculations based on Discrete Dipole Approximation (DDA) for extinction efficiencies of composite dust grains which is made up of a host silicate spheroid and graphite inclusions. The study indicates that smaller dust grains are more efficient for the directions in the galaxy where observed Rv values are found to be low.
Interstellar extinction and polarization - A spheroidal dust grain approach perspective
(2010-01-10) Das, H.K.; Voshchinnikov, N. V.; Il'in, V.B.
We extend and investigate the spheroidal model of interstellar dust grains used to simultaneously interpret the observed interstellar extinction and polarization curves. We compare our model with similar models recently suggested by other authors, study its properties and apply it to ﬁt the normalized extinction A(λ)/AV and the polarizing eﬃciency P(λ)/A(λ) measured in the near IR to far UV region for several stars seen through one large cloud. We conclude that the model parameter Ω being the angle between the line of sight and the magnetic ﬁeld direction can be more or less reliably determined from comparison of the theory and observations. This opens a way to study the spatial structure of interstellar magnetic ﬁelds by using multi-wavelength photometric and polarimetric observations.
Non-adiabatic gravitational collapse of a superdense star
(2010-06-01) Sarwe, S. B.; Tikekar, R.
The relativistic equations governing the non-adiabatic shear-free collapse of massive superdense stars in the presence of dissipative forces producing heat ﬂow in the background of space–times of the Vaidya–Tikekar ansatz with associated physical three-spaces that have the three-spheroidal geometry are formulated. It is shown how the system can be used to examine the development and progress of the collapse during subsequent epochs until the radiating star becomes a black hole.
Odd-parity CMB bispectrum
(2010-10-22) Kamionkowski, Marc; Souradeep, Tarun
Measurement of the cosmic microwave background (CMB) bispectrum, or three-point correlation function, has now become one of the principle eﬀorts in early-Universe cosmology. Here we show that there is a odd-parity component of the CMB bispectrum that has been hitherto unexplored. We argue that odd-parity temperature-polarization bispectra can arise, in principle, through weak lensing of the CMB by chiral gravitational waves or through cosmological birefringence, although the signals will be small even in the best-case scenarios. Measurement of these bispectra requires only modest modiﬁcations to the usual data-analysis algorithms. They may be useful as a consistency test in searches for the usual bispectrum and to search for surprises in the data.
Optical spectroscopy of candidates of young stellar objects in NGC 1333
(2010-12-31) Itoh, Yoichi; et al.; Gupta, Ranjan; Oasa, Yumiko
We carried out low-resolution optical spectroscopy of 14 low-luminosity young stellar object (YSO) candidates in the NGC 1333 cluster. These objects were previously identiﬁed by the near-infrared imaging survey. Eleven objects were conﬁrmed as YSOs by the H line emission. Strengths of the H emission are correlated with the near-infrared excesses of the objects. Spectral types of all YSOs are estimated to be M-type, indicative of low-mass. Comparisons of the results of our spectroscopic observations and the previous photometric observations with evolutionary tracks on the HR diagram suggest two objects to be young brown dwarfs.
Perturbed power-law parameters from WMAP7
(2010-11-19) Minu, Joy; Souradeep, Tarun
We present a perturbative approach for studying inﬂation models with soft departures from scale free spectra of the power law model. In the perturbed power law (PPL) approach one obtains at the leading order both the scalar and tensor power spectra with the running of their spectral indices, in contrast to the widely used slow roll expansion. The PPL spectrum is confronted data and we show that the PPL parameters are well estimated from WMAP-7 data.
Photopolarimetric study of the star-forming clouds CB3,CB25,and CB39
(2010-07-22) Sen, A.K.; et al.; Polcaro, V. F.; Dey, I.
The small compact isolated dark clouds also known as ’Bok globules’ are believed to be ideal sites for low-mass star formation. Some of these clouds are undergoing gravitational collapse, and the ambient magnetic ﬁeld plays a key role in collapse dynamics. The background star polarimetry is generally accepted as a good tool to map the magnetic ﬁeld, which is responsible for the alignment of dichroic grains that produce polarization. Aims. The background star polarization when studied together with extinction is expected to help us to understand various grain properties and the role of polarimetry as a tracer of magnetic ﬁeld in these star-forming clouds. With this idea, polarization and colour excess E(B − V ) values for a set of background stars have been studied together to understand various astrophysical process in some star-forming dark clouds. Methods. Optical photometric observations of the three clouds CB3, CB25, and CB39 were carried out at the 2m H.C. Telescope, India, to determine the colour excess E(B −V ) of the background stars by following a technique adopted by Barnei and Polacaro (2001). These three clouds were selected from a set of eight clouds previously observed by us in optical polarimetry ( Sen et al. 2000). Further independent spectroscopic measurements of a few selected sample stars were recently carried out during February and March 2010 from 1.52m Cassini Telescope, Loinao, Italy, to conﬁrm the correctness of estimated E(B − V ) values obtained by this photometric technique. Results. The colour excess E(B−V ) values so obtained were compared with optical polarization values obtained for the same set of stars. It was found that the measured extinction values increase with the increase in percentage polarization for the cloud CB39 and to some extent for CB25. However, for cloud CB31 no such correlation was observed. It is normally expected that the grains causing extinction should also cause polarization of the light from background stars. Any possible deviation from this under diﬀerent circumstances here has been discussed in the light of the ongoing physical processes in the star-forming clouds.
Polarimetric observations of comet 67P/Churyumov-gerasimenko during its 2008-2009 apparition
(2010-04-01) Hadamcik, E.; et al.; Sen, A.K.; Levasseur-Regourd, A. C.
Remote observations of the light scattered by comet 67P/Churyumov-Gerasimenko dustcoma are of major importance to determine the physical properties of the particles and prepare the rendezvous with the ESA/Rosetta spacecraft in 2014. Aims. Light scattering and especially linear polarization observations allow a comparison between di erent coma regions and di erent comets, including comets that have been studied by space probes. Our aim is to retrieve physical properties of the dust particles and to characterize their evolution around perihelion passage. Methods. Recent imaging polarimetric observations have been conducted at Haute-Provence observatory (France) on 2009 March 17-19 at 35° phase angle and at IUCAA Girawali observatory (India) on 2008 December 25-27 at 36° phase angle and on 2009 April 30-May 1 at 29° phase angle. With the imaging technique, the intensity and linear polarization variations are studied through the various coma regions. These observations are compared to other cometary data (e.g.Jupiter family comets) and to numerical and experimental simulations. Results. The decrease in intensity as a function of the distance to nucleus in log-log scale is on average close to -1, although important variations with values down to -1.5 are noticed, in agreement with previous observations in 1982-83 and 1995-96. The intensity along the tailward direction decreases with a slope between -1.2 two months before perihelion (2009 February 28)to -1.0 two months after perihelion; the decrease is more pronounced in the sunward direction. Before perihelion, aperture polarization values are comparable to polarization values measured on other comets at similar phase angles. The sharp decrease in intensity and the feature in the tailward direction, without any di erence in polarization in the coma before perihelion, could suggest the presence of large dark particles. The post-perihelion increase in intensity and in polarization suggests that an outburst has occurred. The freshly ejected dust polarizes more the scattered light and is more sensitive to the solar radiation pressure, suggesting small micron- or submicron-sized grains. Conclusions. Polarization and intensity variations in the coma of 67P/Churyumov-Gerasimenko are reminiscent of those noticed for some comets such as comet 81P/Wild 2 and comet 9P/Tempel 1. The presence of rather large particles can thus be suggested before and just after perihelion and the ejection of smaller grains, eventually in ﬂu y aggregates post-perihelion. An important sea-sonal e ect related to the obliquity of the comet suggests that the di erent grains originate from di erent hemispheres of the nucleus.