Cooler Component Research Articles

The Photospheric Temperatures of Betelgeuse during the Great Dimming of 2019/2020: No New Dust Required

Abstract The processes that shape the extended atmospheres of red supergiants, heat their chromospheres, create molecular reservoirs, drive mass loss, and create dust remain poorly understood. Betelgeuse’s V-band “Great Dimming” event of 2019 September/2020 February and its subsequent rapid brightening provides a rare opportunity to study these phenomena. Two different explanations have emerged to explain the dimming; new dust appeared in our line of sight attenuating the photospheric light, or a large portion of the photosphere had cooled. Here we present five years of Wing three-filter (A, B, and C band) TiO and near-IR photometry obtained at the Wasatonic Observatory. These reveal that parts of the photosphere had a mean effective temperature (T eff) significantly lower than that found by Levesque & Massey. Synthetic photometry from MARCS-model photospheres and spectra reveal that the V band, TiO index, and C-band photometry, and previously reported 4000–6800 Å spectra can be quantitatively reproduced if there are multiple photospheric components, as hinted at by Very Large Telescope (VLT)-SPHERE images in Montargès et al. If the cooler component has ΔT eff ≥ 250 K cooler than 3650 K, then no new dust is required to explain the available empirical constraints. A coincidence of the dominant short- (∼430 days) and long-period (∼5.8 yr) V-band variations occurred near the time of deep minimum (Guinan et al. 2019a). This is in tandem with the strong correlation of V mag and photospheric radial velocities, recently reported by Dupree et al. (2020b). These suggest that the cooling of a large fraction of the visible star has a dynamic origin related to the photospheric motions, perhaps arising from pulsation or large-scale convective motions.

Global X-Ray Properties of the Vela and Puppis A Supernova Remnants

Abstract The Vela and Puppis A supernova remnants (SNRs) comprise a large emission region of ∼8° diameter in the soft X-ray sky. The HaloSat CubeSat mission provides the first soft X-ray (0.4–7 keV) observation of the entire Vela SNR and Puppis A SNR region with a single pointing and moderate spectral resolution. HaloSat observations of the Vela SNR are best fit with a two-temperature thermal plasma model consisting of a cooler component with keV in collisional ionization equilibrium and a hotter component with keV in nonequilibrium ionization. Observations of the Puppis A SNR are best fit with a single-component plane-parallel shocked plasma model with keV in nonequilibrium ionization. For the first time, we find the total X-ray luminosities of both components of the Vela SNR spectrum in the 0.5–7 keV energy band to be erg s−1 for the cooler component and erg s−1 for the hotter component. We find the total X-ray luminosities of the Vela and Puppis A SNRs to be erg s−1 and erg s−1.

A survey of extended matter around chromospherically active binary systems

AbstractWe present an analysis of colour excess(CE)observations for 13 chromospherically active binary systems, together with 27 inactive reference stars of similar spectral types and luminosity classes of the components of these 13 binaries. We used the observations which were made by Johnson-Cousins${BVR}_{c}\mathrm{I}_{c}$,2MASS, andWISEphotometric systems. Our new photometric${BVR}_{c}\mathrm{I}_{c}$observations were obtained by means of 1 m telescope at TÜBİTAK National Observatory and 40 cm telescope at Ankara University Kreiken Observatory. To check the existence of extended matter around an active binary component(s) of these 13 binary systems, we examined theCEvalues at around primary/secondary minima and outside eclipses. The comparison of theseCEs, obtained relative to those of reference stars of the same${(B-V)_\circ}$colours, especially during primary minima with those of secondary minima and outside eclipses, showed that these systems have greater excess radiation in primary minima than in both secondary minima and outside eclipses. We observed that the colour excesses, in general, most likely arise from the extended matter around the cooler component of a binary system. The comparison ofCEvalues also showed that the extended matter of some of these systems was most likely covered or affected both of their components. Since no observational data were obtained during primary minimum ofRW UMa, by excluding this binary system, an examination of the locations of cool and active components of the remaining 12 systems of this study on Hertzsprung-Russell diagram, together with corresponding evolutionary tracks, showed that most of the active binary systems have an extended matter not only caused from stellar activity but also more likely caused from evolutionary processes.

Analysis of Quiescent Corona X-ray Spectra from SphinX During the 2009 Solar Minimum

The SphinX X-ray spectrophotometer on the {\em CORONAS-PHOTON}\/ mission observed the 1~--~15\,keV X-ray spectrum of the spatially integrated solar corona during the deep minimum of 2009, when solar activity was exceptionally low. Its sensitivity for energies $> 1.2$\,keV was higher than that of any other solar X-ray spectrometer in orbit at the time, including the detectors on GOES. Using much improved instrumental data than was used previously, we analyzed SphinX spectra in 576 intervals for which there was no discernible activity (NA), 40 intervals when there were X-ray brightenings (B), and sixteen intervals when there were micro-flares with peak emission less than GOES A1 (F). An instrumental background spectrum, formed over 34 hours of spacecraft night-time periods and including electronic noise and particle radiation, was subtracted from the solar spectra. Theoretical spectra were used to deduce temperatures on an isothermal assumption for the NA, B, and F intervals (1.69, 1.81, and 1.86\,MK respectively). Differential emission measure (DEM) analysis for the same spectra revealed a "cooler" component (log\,$T = 6.2$ or $T \approx 1.6$\,MK) in each case, but with a second hotter component having a less well-defined peak temperature varying from $\approx 2.5$ to $\approx 3.5$\,MK (log\,$T = 6.4$ and 6.55) and an emission measure between two and three orders smaller than that of the cooler component. These results are similar to those obtained at times just after solar minimum with the EVE instrument. A very hot component that might indicate the signature of nano-flare heating of the corona is not evident in SphinX data.

COS Observations of the Cosmic Web: A Search for the Cooler Components of a Hot, X-Ray Identified Filament

Abstract In the local universe, a large fraction of the baryon content is believed to exist as diffuse gas in filaments. While this gas is directly observable in X-ray emission around clusters of galaxies, it is primarily studied through its UV absorption. Recently, X-ray observations of large-scale filaments connecting to the cosmic web around the nearby (z = 0.05584) cluster A133 were reported. One of these filaments is intersected by the sightline to quasar [VV98] J010250.2−220929, allowing for a first-ever census of cold, cool, and warm gas in a filament of the cosmic web where hot gas has been seen in X-ray emission. Here, we present UV observations with the Cosmic Origins Spectrograph and optical observations with the Magellan Echellette spectrograph of [VV98] J010250.2−220929. We find no evidence of cold, cool, or warm gas associated with the filament. In particular, we set a 2σ upper limit on Lyα absorption of log(N H i /cm−2) < 13.7, assuming a Doppler parameter of b = 20 km s−1. As this sightline is ∼1100 pkpc (0.7R vir) from the center of A133, we suggest that all gas in the filament is hot at this location, or that any warm, cool, or cold components are small and clumpy. A broader census of this system—combining more UV sightlines, deeper X-ray observations, and a larger redshift catalog of cluster members—is needed to better understand the roles of filaments around clusters.

Absolute properties of RU Cnc revisited: an active RS CVn-type eclipsing binary with red giant branch and main-sequence components

ABSTRACT We present observations and analysis of an RS CVn-type double-lined eclipsing binary system, RU Cnc. The system has been observed for over a century. High-quality long-cadence observations, newly obtained from the Kepler K2 C5 and C18 campaigns, and two radial velocity curves were combined and analysed simultaneously, assuming a multispot model. The masses, radii and luminosities of the component stars have been precisely obtained as $M_\textrm{c} = 1.386\pm 0.044\, \mathrm{M}_{\odot }$, $M_\textrm{h} = 1.437 \pm 0.046\, \mathrm{M}_{\odot }$, $R_\textrm{h} = 2.39\pm 0.07\, \mathrm{R}_{\odot }$, $R_\textrm{c} = 5.02 \pm 0.08\, \mathrm{R}_{\odot }$, $L_\textrm{h} = 11.4\pm 1.2\, \mathrm{L}_{\odot }$ and$L_\textrm{c} = 12.0 \pm 1.0\, \mathrm{L}_{\odot }$, with a separation of $a = 27.914 \pm 0.016\, \mathrm{R}_{\odot }$. The distance of the system is determined to be $380\pm 57\,$ pc, which is consistent with the Gaia Data Release 2 result. Long-term detailed period variation analysis of the system indicates a period decrease of 7.9 × 10−7 d yr–1. The results suggest that the cooler component is on the red giant branch (RGB) and the hotter component is still on the main sequence.

Orbital and physical parameters of eclipsing binaries from the All-Sky Automated Survey catalogue

Aims. We present results of the combined photometric and spectroscopic analysis of three detached eclipsing binaries, the secondary components of which are not visible or are very hard to identify in the optical spectra – ASAS J052743–0359.7, ASAS J065134–2211.5, and ASAS J073507–0905.7. The first one is the known visual binary ADS 4022, and we found that it is a quadruple system composed of two spectroscopic binaries, one of which shows eclipses. None of the systems have previously been recognized as a spectroscopic binary.Methods. We used the following telescopes/spectrographs to collect a number of high-resolution optical and IR spectra: Subaru/IRCS, CTIO-1.5 m/CHIRON,Euler/CORALIE, MPG-2.2 m/FEROS, OAO-188/HIDES, and TNG/HARPS-N. We used these data to calculate radial velocities (RVs) and later combined them with MITSuME and ASAS photometry. The Subaru/IRCS IR spectra were crucial for secure identification of the lines of the cooler components. Radial velocity measurements were made with the TODCOR technique, and RV curves were modelled with our own procedure V2FIT. Light-curve modelling was performed with JKTEBOP and PHOEBE codes. Temperatures and metallicities of two systems were estimated from spectra. For the ADS 4022 system we also used the archival WDS data and new SOAR observations in order to derive the orbit of the visual pair for the first time. Ages were estimated by comparing our results with PARSEC isochrones.Results. The eclipsing pair ASAS J052743–0359.7 A (P = 5.27 d) is composed of a 1.03(6)M⊙, 1.03(2)R⊙primary and a 0.60(2)M⊙, 0.59(2)R⊙secondary. The components of theP = 21.57 d non-eclipsing pair B likely have masses in between the two eclipsing components, and both pairs are on a ∼188 yr orbit around their common centre of mass. The system ASAS J065134-2211.5 (P = 8.22 d) consists of a 0.956(12)M⊙, 0.997(4)R⊙primary and a 0.674(5)M⊙, 0.690(7)R⊙secondary. Finally, ASAS J073507-0905.7 (P = 1.45 d), which consists of a 1.452(34)M⊙, 1.635(12)R⊙primary and a 0.808(13)M⊙, 0.819(11)R⊙secondary, is likely a pre-main sequence system. In all cases secondary eclipses are total.

Interstellar Matters: Neutral Hydrogen and the Galactic Magnetic Field

Abstract A very long and nearly straight H i filament at about −60 km s−1 in the southern Galactic hemisphere, seen nearly normal to the line of sight and well separated from low-velocity gas, has been studied in several ways in order to understand its physics, structure, and morphology. Gaussian analysis of 1800 profiles and examination of 140 declination–velocity cross sections shows that an underlying H i component, which is at least 15° long and about 1° wide, has a typical line width of 21 km s−1. It does not appear to be in thermal pressure equilibrium with its surroundings; rather, it may be confined by a magnetic field of 18 μG. Narrow, elongated features (threads), probably unresolved in the 4′ H i observations, have been identified within the boundaries of the filament. In general, each of these threads has two emission components, with line widths of the order of 8 and 3 km s−1, which may wind around each other. Analysis suggests that these cooler components have an average density of 29 cm−3 and may be confined by a magnetic field of 5 μG. These results, taken together, can be explained if this southern filament has magnetic substructure.

Multiscaled Experimental Investigations of Corrosion and Precipitation Processes After Loss-of-Coolant Accidents in Pressurized Water Reactors

In a joint research project of the Zittau/Goerlitz University of Applied Sciences, the Technische Universität Dresden, and the Helmholtz-Zentrum Dresden-Rossendorf, the main emphasis is the time-related assignment of simultaneous and interacting mechanisms at zinc sources and zinc sinks at boundary conditions of a loss-of-coolant accident (LOCA) in German pressurized water reactors (PWRs). The required experiments are carried out at semitechnical and laboratory scales.Zinc is used as a protective coating, e.g., for gratings in the containment, showing high corrosion resistance due to a gradual formation of passivating layers. In contrast, its long-term behavior during LOCA changes significantly under the influence of the coolant chemistry of German PWRs. As a consequence, installations in the containment act as zinc sources. Released zinc ions change the chemical properties of the coolant and could, e.g., lead to layer-forming depositions of zinc borates in the core, which increases the possibility of a hindered heat dissipation. For experimental and methodical investigations of these phenomena, the test rig Zittau flow tray, a scaled sump model of a German PWR, was equipped with a full-length 3 × 3 fuel assembly dummy acting as core model, a preheater, and a cooler component. Nine 4.4-m-long fuel rod dummies simulate the decay heat by internal heating cartridges. This rig design enables experimental investigation of physicochemical mechanisms considering coolant containing boric acid and zinc and their influence on the thermohydraulic processes in the reactor core at post-LOCA boundary conditions. Additional zinc corrosion and zinc borate precipitation studies to elucidate chemical zinc corrosion mechanisms and dependencies of those processes on typical LOCA parameters were carried out using lab-scale corrosion/precipitation test facilities.The time-dependent zinc release at hot-dip galvanized gratings (HGGs) was investigated regarding their position (e.g., inside or near the leaking jet, freely suspended, or submerged in the coolant) and their surface area as well as the temperature and flow rate of the coolant. The experimental database allows the approximation of corrosion rates in dependence of HGG position and the accident-specific coolant leakage rate as well as first mathematical approaches for the modeling of zinc sources.

Dust around the Cool Component of D-Type Symbiotic Binaries

D type symbiotic binaries are an excellent astrophysical laboratory for investigation of the dust properties and dust formation under the influence of theMira stellar wind and nova activity and of the mass loss and mass transfer between components in such a widely separated system. We present a study of the properties of circumstellar dust in symbiotic Miras by use of long-term near-IR photometry and colour indices. The published JHKL magnitudes of o Ceti, RX Pup, KM Vel, V366 Car, V835 Cen, RR Tel, HM Sge and R Aqr have been collected, analyzed and corrected for short-term variations caused by Mira pulsations. Assuming spherical temperature distribution of the dust in the close neighbourhood of the Mira, the DUSTY code was used to solve the radiative transfer in order to determine the dust temperature and its properties in each particular case. Common dust properties of the symbiotic Miras have been found, suggesting similar conditions in the condensation region of the studied symbiotic Miras. Silicate dust with the inner dust shell radius determined by the dust condensation and with the dust temperature of 900−1200 K can fully explain the observed colour indices. R Aqr is an exception and showed lower dust temperature of 650 K. Obscuration events visible in light curves can be explained by variable dust optical depth with minimal variations of other dust properties. More active symbioticMiras that underwent recent nova outbursts showed higher dust optical depths and larger maximum grain sizes of the order of μm, which means that the post-nova activity could stimulate the dust formation and the grain growth. Optically thicker dust shells and higher dust condensation temperatures have been found in symbiotic Miras compared to their single counterparts, suggesting different conditions for dust production.

On a Solar Blowout Jet: Driving Mechanism and the Formation of Cool and Hot Components

Abstract We present observations of a blowout jet that experienced two distinct ejection stages. The first stage started from the emergence of a small positive magnetic polarity, which was cancelled by the nearby negative magnetic field and caused the rising of a mini-filament and its confining loops. This further resulted in a small jet due to the magnetic reconnection between the rising confining loops and the overlying open field. The second ejection stage was mainly due to successive removal of the confining field by reconnection: the filament erupted, and the erupting cool filament material directly combined with the hot jet that originated form the reconnection region and therefore formed the cool and hot components of the blowout jet. During the two ejection stages, cool Hα jets are also observed cospatial with their coronal counterparts, but their appearance times are earlier by a few minutes than those of the hot coronal jets. The hot coronal jets are therefor possibly caused by the heating of the cool Hα jets or the rising of the reconnection height from the chromosphere to the corona. The scenario that magnetic reconnection occurred between the confining loops and the overlying open loops is supported by many observational facts, including the bright patches on both sides of the mini-filament, hot plasma blobs along the jet body, and periodic metric radio type III bursts at the very beginnings of the two stages. The evolution and characteristics of these features show the detailed nonlinear process in magnetic reconnection.

Performance analysis of a new ejector expansion refrigeration cycle (NEERC) for power and cold: Exergy and energy points of view

In the present work, a new CO2 refrigeration cycle, with the ejector expansion cycle serving as a harvesting tool of gas cooler wasted heat, is investigated. An attempt has been made to harvest and utilize the low-grade wasted energy, in the gas cooler component of the refrigeration basic cycle, through a transcritical carbon dioxide Rankine cycle. The work produced by the new cycle is used to drive the compressor and the feed pump, hence reducing the consumption work input and, as a result, it will enhance the performance characteristics of the whole system. The system operating and performance characteristics are investigated theoretically by energetic and exergetic methods. The simulation results were obtained by a computer FORTRAN program, where REFPROP 9 database was used to get the refrigerant thermodynamic properties. The simulation results showed that the proposed new refrigeration ejector expansion cycle (NEERC) had higher coefficient of performance and higher system second law efficiency in compare to the basic ejector expansion refrigeration cycle (BEERC). An enhancement of 12% in the COP and exergy efficiency of NEERC was found in comparison with BEERC when the cooling capacity and operating conditions of the two systems were the same. The increase of COP of NEERC and its efficiency along with the reduction of power consumption make it more practical for the use in residential air conditioning and cooling applications. A techno-economic analysis to compare ORC with Rankine cycle is provided. The results indicated that Rankine cycle for transcritical CO2 refrigeration cycle is more appropriate and has an advantage over the use of ORC. In addition, the small scale Rankine cycle combined with BEERC is economically viable for countries where the electricity price is above 15 c€/kWh.

Very High Excitation Lines of H2 in the Orion Molecular Cloud Outflow

Abstract Vibration–rotation lines of H2 from highly excited levels approaching the dissociation limit have been detected at a number of locations in the shocked gas of the Orion Molecular Cloud (OMC-1), including in a Herbig–Haro object near the tip of one of the OMC-1 “fingers.” Population diagrams show that, while the excited H2 is almost entirely at a kinetic temperature of ∼1800 K (typical for vibrationally shock-excited H2), as in the previously reported case of Herbig–Haro object HH 7 up to a few percent of the H2 is at a kinetic temperature of ∼5000 K. The location with the largest fraction of hot H2 is the Herbig–Haro object, where the outflowing material is moving at a higher speed than at the other locations. Although theoretical work is required for a better understanding of the 5000 K H2 (including how it cools), its existence and the apparent dependence of its abundance relative to that of the cooler component on the relative velocities of the outflow and the surrounding ambient gas appear broadly consistent with it having recently reformed. The existence of this high-temperature H2 appears to be a common characteristic of shock-excited molecular gas.

Energetic and exergetic performance investigation of a cement facility for clinker production

In this study, the energetic and exergetic analyses of a cement plant for clinker production are investigated. The exergy destruction rate, energy and exergy efficiency of process components are presented by using the thermodynamic balance equations. The energetic and exergetic efficiencies of cement plant are calculated as 60.78%, and 46.11%, respectively. The rotary kiln, raw mill and cooler component have the maximum exergy destruction rate among the other process components. The exergy efficiency of rotary kiln, raw mill and cooler component are calculated as 57.36%, 33.52% and 49.46%, respectively. Also, to analyse the cement plant performance more comprehensively, the parametric studies are conducted to determine the impacts of different design variables, such as rotary kiln temperature and raw material mass flow rate, and feedstock coal chemical properties and varying of ambient temperature on the energy efficiency, exergy efficiency and exergy destruction rate of plant components.

The Light Curve and the Orbital Period Variations of Binary System TT Andromedae

The first photoelectric light curve analysis of the TT And system in a broad band filter (400 - 700 nm) was carried out using the PHOEBE program. The absolute dimensions of the system are determined and its evolution is discussed. The most distinct feature of the system is a comparatively very low mass of the cooler component i.e. M2 = 0.26M⊙. Moreover, using the Observed-minus-Calculated data, the period changes of the system are studied, which reveal the presence of a third body orbiting the system with a period P3 = 63.89 yr, superimposed on which is a secular period increase, which is ascribed to mass transfer with a rate −7.60 × 10−12 M⊙ yr−1 from the cooler secondary component.

A HOT COMPANION TO A BLUE STRAGGLER IN NGC 188 AS REVEALED BY THE ULTRA-VIOLET IMAGING TELESCOPE (UVIT) ON ASTROSAT

ABSTRACT We present early results from the Ultra-Violet Imaging Telescope (UVIT) on board the ASTROSAT observatory. We report the discovery of a hot companion associated with one of the blue straggler stars (BSSs) in the old open cluster, NGC 188. Using fluxes measured in four filters in UVIT’s far-UV (FUV) channel, and two filters in the near-UV (NUV) channel, we have constructed the spectral energy distribution (SED) of the star WOCS-5885, after combining with flux measurements from GALEX, Ultraviolet Imaging Telescope, Ultraviolet Optical Telescope, SPITZER, WISE, and several ground-based facilities. The resulting SED spans a wavelength range of 0.15 μm to 7.8 μm. This object is found to be one of the brightest FUV sources in the cluster. An analysis of the SED reveals the presence of two components. The cooler component is found to have a temperature of 6000 ± 150 K, confirming that it is a BSS. Assuming it to be a main-sequence star, we estimate its mass to be ∼1.1–1.2 M ⊙. The hotter component, with an estimated temperature of 17,000 ± 500 K, has a radius of ∼ 0.6 R ⊙ and L ∼30 L ⊙. Bigger and more luminous than a white dwarf, yet cooler than a sub-dwarf, we speculate that it is a post-AGB/HB star that has recently transferred its mass to the BSS, which is known to be a rapid rotator. This binary system, which is the first BSS with a post-AGB/HB companion identified in an open cluster, is an ideal laboratory to study the process of BSS formation via mass transfer.

Two W-subtype contact binaries: GQ Boo and V1367 Tau

Two contact binaries, GQ Boo and V1367 Tau, were observed and analysed with a new method to obtain the absolute parameters. The light-curve analysis shows that both of them are obvious W-subtype contact binaries, with much more massive but apparently cooler components (M-2/M-1 similar or equal to 2 and 4, T-2/T-1 similar or equal to 0.95 and 0.94). The orbital periods were studied using the O-C diagrams, and it is thought that the minima timings were heavily affected by the long-standing magnetic activities on the star surface, so the minima timings cannot represent the real period changes. The mass-radius relationships were proposed by the light-curve analysis alone, which is equivalent to the mean density. The density and temperature can determine the other absolute parameters in most of the time. With the almost complete star parameter space provided by PARSEC, approximate masses and radii were obtained (0.52 +/- 0.08M(circle dot) and 1.01 +/- 0.15M(circle dot) for GQ Boo, and 0.22 +/- 0.01M(circle dot) and 0.92 +/- 0.06M(circle dot) for V1367 Tau). The mass-radius relationship is a neglected useful tool to calculate the mass and radius, especially for the detached binaries.

A solar twin in the eclipsing binary LL Aquarii

In the course of a project to study eclipsing binary stars in vinicity of the Sun, we found that the cooler component of LL Aqr is a solar twin candidate. This is the first known star with properties of a solar twin existing in a non-interacting eclipsing binary, offering an excellent opportunity to fully characterise its physical properties with very high precision. We used extensive multi-band, archival photometry and the Super-WASP project and high-resolution spectroscopy obtained from the HARPS and CORALIE spectrographs. The spectra of both components were decomposed and a detailed LTE abundance analysis was performed. The light and radial velocity curves were simultanously analysed with the Wilson-Devinney code. The resulting highly precise stellar parameters were used for a detailed comparison with PARSEC, MESA, and GARSTEC stellar evolution models. LL Aqr consists of two main-sequence stars (F9 V + G3 V) with masses of M1 = 1.1949$\pm$0.0007 and M2=1.0337$\pm$0.0007 $M_\odot$, radii R1 = 1.321$\pm$0.006 and R2 = 1.002$\pm$0.005 $R_\odot$, temperatures T1=6080$\pm$45 K and T2=5703$\pm$50 K and solar chemical composition [M/H]=0.02$\pm$0.05 dex. The absolute dimensions, radiative and photometric properties, and atmospheric abundances of the secondary are all fully consistent with being a solar twin. Both stars are cooler by about 3.5 $\sigma$ or less metal abundant by 5$\sigma$ than predicted by standard sets of stellar evolution models. When advanced modelling was performed, we found that full agreement with observations can only be obtained for values of the mixing length and envelope overshooting parameters that are hard to accept. The most reasonable and physically justified model fits found with MESA and GARSTEC codes still have discrepancies with observations but only at the level of 1$\sigma$.

ABSOLUTE PARAMETERS AND PHYSICAL NATURE OF THE LOW-AMPLITUDE CONTACT BINARY HI DRACONIS

We present a detailed investigation of the low-amplitude contact binary HI Dra based on the new VRcIc CCD photometric light curves (LCs) combined with published radial velocity (RV) curves. Our completely covered LCs were analyzed using PHOEBE and revealed that HI Dra is an overcontact binary with low fill-out factor f = 24 ± 4(%) and temperature difference between the components of 330 K. Two spotted models are proposed to explain the LC asymmetry, between which the A subtype of W UMa type eclipsing systems, with a cool spot on the less massive and cooler component, proves to be more plausible on evolutionary grounds. The results and stability of the solutions were explored by heuristic scan and parameter perturbation to provide a consistent and reliable set of parameters and their errors. Our photometric modeling and RV curve solution give the following absolute parameters of the hot and cool components, respectively: Mh = 1.72 ± 0.08 and Mc = 0.43 ± 0.02 , Rh = 1.98 ± 0.03 and Rc = 1.08 ± 0.02 , and Lh = 9.6 ± 0.1 and Lc = 2.4 ± 0.1 . Based on these results the initial masses of the progenitors (1.11 ± 0.03 and 2.25 ± 0.07 , respectively) and a rough estimate of the age of the system of 2.4 Gyr are discussed.

MAPPING THE SURFACE OF THE MAGNETAR 1E 1048.1–5937 IN OUTBURST AND QUIESCENCE THROUGH PHASE-RESOLVED X-RAY SPECTROSCOPY

We model the pulse profiles and the phase resolved spectra of the anomalous X-ray pulsar 1E 1048.1-5937 obtained with XMM-Newton to map its surface temperature distribution during an active and a quiescent epoch. We develop and apply a model that takes into account the relevant physical and geometrical effects on the neutron star surface, magnetosphere, and spacetime. Using this model, we determine the observables at infinity as a function of pulse phase for different numbers and sizes of hot spots on the surface. We show that the pulse profiles extracted from both observations can be modeled with a single hot spot and an antipodal cool component. The size of the hot spot changes from $\approx 80^{\circ}$ in 2007, 3 months after the onset of a dramatic flux increase, to $\approx 30^{\circ}$ during the quiescent observation in 2011, when the pulsed fraction returned to the pre-outburst $\approx$ 65\% level. For the 2007 observation, we also find that a model consisting of a single 0.4 keV hot spot with a magnetic field strength of $1.8 \times 10^{14}$ G accounts for the spectra obtained at three different pulse phases but under predicts the flux at the pulse minimum, where the contribution to the emission from the cooler component is non-negligible. The inferred temperature of the spot stays approximately constant between different pulse phases, in agreement with a uniform temperature, single hot spot model. These results suggest that the emitting area grows significantly during outbursts but returns to its persistent and significantly smaller size within a few year timescale.