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Ýlgili Makaleler
Warm H2O and OH Disk Emission in V1331 Cyg
We present high-resolution (R = 24, 000) L-band spectra of the youngintermediate-mass star V1331 Cyg obtained with NIRSPEC on the Keck IItelescope. The spectra show strong, rich emission from water and OH thatlikely arises from the warm surface region of the circumstellar disk. Weexplore the use of the new BT2 water line list in fitting the spectra,and we find that it does a much better job than the well-known HITRANwater line list in the observed wavelength range and for the warmtemperatures probed by our data. By comparing the observed spectra withsynthetic disk emission models, we find that the water and OH emissionlines have similar widths (FWHM ~= 18 km s-1). If the linewidths are set by disk rotation, the OH and water emission lines probe asimilar range of disk radii in this source. The water and OH emissionare consistent with thermal emission for both components at atemperature ~1500 K. The column densities of the emitting water and OHare large, ~1021 cm-2 and ~1020cm-2, respectively. Such a high column density of water ismore than adequate to shield the disk midplane from external UVirradiation in the event of complete dust settling out of the diskatmosphere, enabling chemical synthesis to continue in the midplanedespite a harsh external UV environment. The large OH-to-water ratio issimilar to expectations for UV irradiated disks, although the large OHcolumn density is less easily accounted for.Data presented herein were obtained at the W. M. Keck Observatory fromtelescope time allocated to the National Aeronautics and SpaceAdministration through the agency's scientific partnership with theCalifornia Institute of Technology and the University of California. TheObservatory was made possible by the generous financial support of theW. M. Keck Foundation.
| Simultaneous X-Ray and Radio Observations of Young Stellar Objects in NGC 1333 and IC 348
Young stellar objects (YSOs) and in particular protostars are known toshow a variety of high-energy processes. Observations in the X-ray andcentimetric radio wavelength ranges are thought to constrain some ofthese processes, e.g., coronal-type magnetic activity. There is awell-known empirical correlation of radio and X-ray luminosities inactive stars, the so-called Güdel-Benz (GB) relation. Previousevidence of whether YSOs are compatible with this relation remainsinconclusive for the earliest evolutionary stages. The main difficultyis that due to the extreme variability of these sources, simultaneousobservations are essential. Until now, only a few YSOs and only ahandful of protostars have been observed simultaneously in the X-ray andradio range. To expand the sample, we have obtained such observations oftwo young clusters rich in protostars, NGC 1333 and IC 348. While theabsolute sensitivity is lower for these regions than for more nearbyclusters like CrA, we find that even in deep continuum observationscarried out with the NRAO Very Large Array (VLA), the radio detectionfraction for protostars in these clusters is much lower than the X-raydetection fraction. Very few YSOs are detected in both bands, and wefind the radio and X-ray populations among YSOs to be largely distinct.We combine these new results with previous simultaneous Chandra and VLAobservations of star-forming regions and find that YSOs with detectionsin both bands appear to be offset toward higher radio luminosities forgiven X-ray luminosities when compared with the GB relation, althougheven in this sensitive data set most sources are too weak for the radiodetections to provide information on the emission processes. Theconsiderably improved sensitivity of the Expanded VLA will provide abetter census of the YSO radio population as well as better constraintson the emission mechanisms.
| PTF10nvg: An Outbursting Class I Protostar in the Pelican/North American Nebula
During a synoptic survey of the North American Nebula region, thePalomar Transient Factory (PTF) detected an optical outburst (dubbedPTF10nvg) associated with the previously unstudied flat or risingspectrum infrared source IRAS 20496+4354. The PTF R-band light curvereveals that PTF10nvg brightened by more than 5 mag during the currentoutburst, rising to a peak magnitude of R PTF ? 13.5 in2010 September. Follow-up observations indicate that PTF10nvg hasundergone a similar ~5 mag brightening in the K band and possesses arich emission-line spectrum, including numerous lines commonly assumedto trace mass accretion and outflows. Many of these lines areblueshifted by ~175 km s-1 from the North American Nebula'srest velocity, suggesting that PTF10nvg is driving an outflow. Opticalspectra of PTF10nvg show several TiO/VO band heads fully in emission,indicating the presence of an unusual amount of dense(>1010 cm-3), warm (1500-4000 K) circumstellarmaterial. Near-infrared spectra of PTF10nvg appear quite similar to aspectrum of McNeil's Nebula/V1647 Ori, a young star which has undergoneseveral brightenings in recent decades, and 06297+1021W, a Class Iprotostar with a similarly reached near-infrared emission line spectrum.While further monitoring is required to fully understand this event, weconclude that the brightening of PTF10nvg is indicative of enhancedaccretion and outflow in this Class-I-type protostellar object, similarto the behavior of V1647 Ori in 2004-2005.
| Spitzer Observations of Supernova Remnants. II. Physical Conditions and Comparison with HH7 and HH54
We have studied the shock-excited molecular regions associated with foursupernova remnants (SNRs)—IC443C, W28, W44, and 3C391—andtwo Herbig-Haro objects—HH7 and HH54—using Spitzer'sInfrared Spectrograph (IRS). The physical conditions within the observedareas (roughly ~1' × 1' in size) are inferred from spectroscopicdata obtained from IRS and from the Short and Long WavelengthSpectrometers on board the Infrared Space Observatory (ISO), togetherwith photometric data from Spitzer's Infrared Array Camera. Adopting apower-law distribution for the gas temperature in the observed region,with the mass of gas at temperature T to T+dT assumed proportional to T-b dT, the H2 S(0) to S(7) spectral line mapsobtained with IRS were used to constrain the gas density, yieldingestimated densities n(H2) in the range of ~(2-4)×103 cm-3. The excitation ofH2 S(9) to S(12) and high-J CO pure rotational lines,however, require environments several times denser. The inconsistencyamong the best-fit densities estimated from different species can beexplained by density fluctuations within the observed regions. Thebest-fit power-law index b is smaller than the value 3.8 predicted for aparaboloidal C-type bow shock, suggesting that the shock front has a"flatter" shape than that of a paraboloid. The best-fit parameters forSNRs and Herbig-Haro objects do not differ significantly between the twoclasses of sources, except that for the SNRs the ortho-to-para ratio(OPR) of hot gas (T> 1000 K) is close to the local thermalequilibrium value 3, while for HH7 and HH54 even the hottest gasexhibits an OPR smaller than 3; we interpret this difference asresulting from environmental differences between these classes ofsources, molecular material near SNRs being subject to strongerphotodissociation that results in faster para-to-ortho conversion.Finally, we mapped the physical parameters within the regions observedwith IRS and found that the mid-lying H2 emissions—S(3)to S(5)—tend to trace the hot component of the gas, while theintensities of S(6) and S(7) are more sensitive to the density of thegas compared to S(3) to S(5).
| Outflow-Core Interaction in Barnard 1
In order to study how outflows from protostars influence the physicaland chemical conditions of the parent molecular cloud, we have observedthe Barnard 1 (B1) main core, which harbors four Class 0 and three ClassI sources, in the CO (J = 1 - 0), CH3OH (JK =2 K - 1 K ), and the SiO (J = 1 - 0) lines usingthe Nobeyama 45 m telescope. We have identified three CO outflows inthis region: one is an elongated (~0.3 pc) bipolar outflow from a Class0 protostar B1-c in the submillimeter clump SMM 2, another is a rathercompact (~0.1 pc) outflow from a Class I protostar B1 IRS in the clumpSMM 6, and the other is an extended outflow from a Class I protostar inSMM 11. In the western lobe of the SMM 2 outflow, both the SiO andCH3OH lines show broad redshifted wings with the terminalvelocities of 25 km s-1 and 13 km s-1,respectively. It is likely that the shocks caused by the interactionbetween the outflow and ambient gas enhance the abundance of SiO andCH3OH in the gas phase. The total energy input rate by theoutflows (1.1 × 10-3 L sun) is smaller thanthe energy-loss rate (8.5 × 10-3 L sun)through the turbulence decay in the B1 main core, which suggests thatthe outflows cannot sustain the turbulence in this region. Since theoutflows are energetic enough to compensate the dissipating turbulenceenergy in the neighboring, more evolved star-forming region NGC 1333, wesuggest that the turbulence energy balance depends on the evolutionarystate of the star formation in molecular clouds.
| Spitzer Mapping of Molecular Hydrogen Pure Rotational Lines in NGC 1333: A Detailed Study of Feedback in Star Formation
We present mid-infrared spectral maps of the NGC 1333 star-formingregion, obtained with the infrared spectrometer on board the SpitzerSpace Telescope. Eight pure H2 rotational lines, from S(0) toS(7), are detected and mapped. The H2 emission appears to beassociated with the warm gas shocked by the multiple outflows present inthe region. A comparison between the observed intensities and thepredictions of detailed shock models indicates that the emission arisesin both slow (12-24 km s-1) and fast (36-53 kms-1) C-type shocks with an initial ortho-to-para ratio (opr)lsim1. The present H2 opr exhibits a large degree of spatialvariations. In the postshocked gas, it is usually about 2, i.e., closeto the equilibrium value (~3). However, around at least two outflows, weobserve a region with a much lower (~0.5) opr. This region probablycorresponds to gas which has been heated up recently by the passage of ashock front, but whose ortho-to-para has not reached equilibrium yet.This, together with the low initial opr needed to reproduce the observedemission, provide strong evidence that H2 is mostly in paraform in cold molecular clouds. The H2 lines are found tocontribute to 25%-50% of the total outflow luminosity, and thus can beused to ascertain the importance of star formation feedback on the natalcloud. From these lines, we determine the outflow mass loss rate and,indirectly, the stellar infall rate, the outflow momentum and thekinetic energy injected into the cloud over the embedded phase. Thelatter is found to exceed the binding energy of individual cores,suggesting that outflows could be the main mechanism for coredisruption.
| High Angular Resolution Radio Observations of the HL/XZ Tau Region: Mapping the 50 AU Protoplanetary Disk Around HL Tau and Resolving XZ Tau S Into a 13 AU Binary
We present new 7 mm and archive 1.3 cm high angular resolutionobservations of the HL/XZ Tau region made with the Very Large Array. At7 mm, the emission from HL Tau seems to arise in a clumpy disk withradius of the order of 25 AU. The 1.3 cm emission from XZ Tau shows theemission from a binary system with 0farcs3 (42 AU) separation, knownfrom previous optical/IR observations. However, at 7 mm, the southernradio component resolves into a binary with 0farcs09 (13 AU) separation,suggesting that XZ Tau is actually a triple star system. We suggest thatthe remarkable ejection of gas from the XZ Tau system observed with theHubble Space Telescope may be related to a periastron passage of thisnewly discovered close binary system.
| Near-Infrared Spectroscopic Monitoring of EXor Variables: First Results
We present low-resolution (R ˜ 250) spectroscopy in the near-IR(0.8-2.5 ?m) of the EXor variables. These are the initial results(obtained during the period 2007-2008) from a long-term photometric andspectroscopic program aimed to study the variability in the accretionprocesses of pre-main-sequence stars, by correlating the continuumfluctuations with the spectroscopic properties. Eight sources have beenobserved in different epochs, for a total of 25 acquired spectra. EXorspectra show a wide variety of emission features dominated by H Irecombination (Paschen and Brackett series). We have investigatedwhether line and continuum variability could be due to a variableextinction, but such a hypothesis is applicable only to the peculiarsource PV Cep. By comparing the observed spectra with a wind model, massloss rates in the range (2-10) × 10-8 M sunyr-1 are derived, along with other wind parameters.Consistent results are also obtained by assuming that H I lines are dueto accretion. A CO overtone is also detected in the majority of thesources both in absorption and in emission. It appears to come fromregions more compact than winds, likely the stellar photosphere (when inabsorption) and the circumstellar disk (when in emission). Na I and Ca IIR lines behave as the CO does, thus they are thought to arise in thesame locations. For some targets multiple spectra correspond todifferent activity stages of the source. Those exhibiting the largestcontinuum variation at 2 ?m (?K gsim 1 mag) present asignificant line flux fading during the continuum declining phases. Inparticular, CO absorption (emission) appears associated with inactive(active) stages, respectively.Based on observations collected at the AZT-24 telescope (CampoImperatore, Italy).
| BAV-Results of observations - Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| New absolute magnitude calibrations for W Ursa Majoris type binaries
Parallaxes of W UMa stars in the Hipparcos catalogue have been analyzed.31 W UMa stars, which have the most accurate parallaxes(σπ/π<0.15) which are neither associated with aphotometric tertiary nor with evidence of a visual companion, wereselected for re-calibrating the Period-Luminosity-Color (PLC) relationof W UMa stars. Using the Lutz-Kelker (LK) bias corrected (mostprobable) parallaxes, periods ({0.26< P< 0.87}, P in days), andcolors ({0.04<(B-V)0<1.28}) of the 31 selected W UMa,the PLC relation have been revised and re-calibrated. The differencebetween the old (revised but not bias corrected) and the new (LK biascorrected) relations are almost negligible in predicting the distancesof W UMa stars up to about 100 pc. But, it increases and may becomeintolerable as distances of stars increase. Additionally, using(J-H)0 and (H-K_s)0 colors from 2MASS (Two MicronAll Sky Survey) data, a PLC relation working with infrared data wasderived. It can be used with infrared colors in the range-0.01<(J-H)0<0.58, and{-0.10<(H-K_s)0<0.18}. Despite of the fact that the2MASS data refer to single epoch observations which are not guaranteedto be taken at maximum brightness of the W UMa stars, the establishedrelation has been found surprisingly consistent and reliable inpredicting LK corrected distances of W UMa stars.
| GSC 4181-0713 - A new W UMa type eclipsing binary.
Not Available
| Proper Motions of Thermal Radio Sources Near HH 7-11 in the NGC 1333 Star-Forming Region
Star-forming regions are expected to show linear proper motions due tothe relative motion of the Sun with respect to the region. These propermotions appear superposed to the proper motions expected in featuresassociated with mass ejection from the young stellar objects embedded inthem. Therefore, it is necessary to have good knowledge of the propermotion of the region as a whole in order to correctly interpret themotions associated with mass ejection. In this paper, we present thefirst direct measurement of proper motions of the NGC 1333 star-formingregion. This region harbors one of the most studied Herbig-Haro systems,HH 7-11, whose exciting source remains unclear. Using Very Large Array Aconfiguration data at 3.6 cm taken over 10 years, we have been able tomeasure the absolute proper motions of four thermal sources embedded inNGC 1333. From our results we have derived the mean proper motions ofthe NGC 1333 star-forming region to be ??cos ?= 9 ± 1 mas yr-1 and ?? = -10± 2 mas yr-1. In this paper, we also discuss thepossible implications of our results in the identification of theoutflow exciting sources.
| B.R.N.O. Times of minima
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| Angular momentum and mass evolution of contact binaries
Various scenarios of contact binary evolution have been proposed in thepast, giving hints of (sometimes contradictory) evolutionary sequencesconnecting A- and W-type systems. As the components of close detachedbinaries approach each other and contact binaries are formed, followingevolutionary paths transforms them into systems of two categories:A-type and W-type. The systems evolve in a similar way but underslightly different circumstances. The mass/energy transfer rate isdifferent, leading to quite different evolutionary results. Analternative scenario of evolution in contact is presented and discussed,based on the observational data of over one hundred low-temperaturecontact binaries. It results from the observed correlations amongcontact binary physical and orbital parameters. Theoretical tracks arecomputed assuming angular momentum loss from a system via stellar wind,accompanied by mass transfer from an advanced evolutionary secondary tothe main-sequence primary. A good agreement is seen between the tracksand the observed graphs. Independently of details of the evolution incontact and a relation between A- and W-type systems, the ultimate fateof contact binaries involves the coalescence of both components into asingle fast rotating star.
| The evolutionary status of W Ursae Majoris-type systems
Well-determined physical parameters of 130 W Ursae Majoris (W UMa)systems were collected from the literature. Based on these data, theevolutionary status and dynamical evolution of W UMa systems areinvestigated. It is found that there is no evolutionary differencebetween W- and A-type systems in the M-J diagram, which is consistentwith the results derived from the analysis of observed spectral type andof M-R and M-L diagrams of W UMa systems. M-R and M-L diagrams of W- andA-type systems indicate that a large amount of energy should betransferred from the more massive to the less massive component, so thatthey are not in thermal equilibrium and undergo thermal relaxationoscillation. Moreover, the distribution of angular momentum, togetherwith the distribution of the mass ratio, suggests that the mass ratio ofthe observed W UMa systems decreases with decreasing total mass. Thiscould be the result of the dynamical evolution of W UMa systems, whichsuffer angular momentum loss and mass loss as a result of the magneticstellar wind. Consequently, the tidal instability forces these systemstowards lower q values and finally to rapidly rotating single stars.
| B.R.N.O. Contributions #34
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| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| New Minima Times of Selected Eclipsing Binaries
We present 169 CCD and photoelectric times of minima of selectedeclipsing binaries obtained from 2005 to 2007 at observatories inSlovakia
| Formation and Evolution of W Ursae Majoris Contact Binaries
The origin and evolution of W UMa systems are discussed based on All SkyAutomated Survey (ASAS) data and the mean kinematic ages of foursubgroups of 97 field contact binaries (FCBs). The period distributionof eclipsing binaries discovered by ASAS suggests that a period limit totidal locking for the close binaries is about 2.24 days, so that most WUMa systems might be formed from detached binaries with periodsP<~2.24 days, and a maximum advanced time from a detached system to aW UMa is about 3.23 Gyr. Moreover, the secular evolution of the angularmomentum (AM), the system mass, and the orbital period of 97 FCBs wereinvestigated according to the mean kinematic ages, which were setaccording to AM bins. AMs, systemic masses, and orbital periods wereshown to be decreasing with kinematic age. Their first-order decreasingrates have been determined as J˙/J=1.86×10-10yr-1, M˙/M=0.95×10-10 yr-1,and P˙/P=1.24×10-10 yr-1, and theaverage amplification (A¯=dlnJ/dlnM) is derived to be 1.96. Theseare lower than those derived from detached chromospherically activebinaries (CABs). This suggests that the magnetic activity level of FCBsis indeed weaker than that of CABs. Meanwhile, the decreasing rate of AMof FCBs is found to be equal to an average value in a cycle of a cyclicmodel of contact binaries. This might suggest that the evolution of FCBsundergoes thermal relaxation oscillation (TRO) and that the coalescenceof W UMa systems is a very long process, which is also indicated by thedynamical evolution of FCBs.
| CCD Minima for Selected Eclipsing Binaries in 2007
Not Available
| Dynamical evolution of active detached binaries on the logJo-logM diagram and contact binary formation
Orbital angular momentum (OAM, Jo), systemic mass (M) andorbital period (P) distributions of chromospherically active binaries(CAB) and W Ursae Majoris (W UMa) systems were investigated. Thediagrams of and logJo-logM were formed from 119 CAB and 102 WUMa stars. The logJo-logM diagram is found to be mostmeaningful in demonstrating dynamical evolution of binary star orbits. Aslightly curved borderline (contact border) separating the detached andthe contact systems was discovered on the logJo-logM diagram.Since the orbital size (a) and period (P) of binaries are determined bytheir current Jo, M and mass ratio, q, the rates of OAM loss(dlogJo/dt) and mass loss (dlogM/dt) are primary parametersto determine the direction and the speed of the dynamical evolution. Adetached system becomes a contact system if its own dynamical evolutionenables it to pass the contact border on the logJo-logMdiagram. The evolution of q for a mass-losing detached system is unknownunless the mass-loss rate for each component is known. Assuming q isconstant in the first approximation and using the mean decreasing ratesof Jo and M from the kinematical ages of CAB stars, it hasbeen predicted that 11, 23 and 39 per cent of current CAB stars wouldtransform to W UMa systems if their nuclear evolution permits them tolive 2, 4 and 6 Gyr, respectively.
| A Photometric Study of the Contact Binary System FU Dra
This paper reports new four-filter CCD observations of the contactbinary FU Dra. The Wilson and Devinney model was used to simultaneouslyfit these light curves and published radial velocity data. The stellarmasses, sizes, and densities were calculated. Five additional modelsinvolving dark spots, hot spots, and accretion heating were consideredas explanations for the light curve asymmetry known as the "O'Connelleffect" in FU Dra. No conclusive spot model choice could be made but theLiu and Yang model for accretion heating is an unlikely explanation forthe O'Connell effect in FU Dra.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Contact Binaries with Additional Components. II. A Spectroscopic Search for Faint Tertiaries
It is unclear how very close binary stars form, given that during thepre-main-sequence phase the component stars would have been inside eachother. One hypothesis is that they formed farther apart but were broughtin closer after formation by gravitational interaction with a thirdmember of the system. If so, all close binaries should be members oftriple (or higher order) systems. As a test of this prediction, wepresent a search for the signature of third components in archivalspectra of close binaries. In our sample of 75 objects, 23 show evidencefor the presence of a third component, down to a detection limit oftertiary flux contributions of about 0.8% at 5200 Å (consideringonly contact and semidetached binaries, we find 20 out of 66). In ahomogeneous subset of 59 contact binaries, we are fairly confident thatthe 15 tertiaries we have detected are all tertiaries present with massratios 0.28<~M3/M12<~0.75 and implied outerperiods P<~106 days. We find that if the frequency oftertiaries were the same as that of binary companions to solar-typestars, one would expect to detect about 12 tertiaries. In contrast, ifall contact binaries were in triple systems, one would expect about 20.Thus, our results are not conclusive but are sufficiently suggestive towarrant further studies.
| 165. List of Timings of Minima Eclipsing Binaries by BBSAG Observers
Not Available
| A catalogue of eclipsing variables
A new catalogue of 6330 eclipsing variable stars is presented. Thecatalogue was developed from the General Catalogue of Variable Stars(GCVS) and its textual remarks by including recently publishedinformation about classification of 843 systems and making correspondingcorrections of GCVS data. The catalogue1 represents thelargest list of eclipsing binaries classified from observations.
| A Catalog of 1022 Bright Contact Binary Stars
In this work we describe a large new sample of contact binary starsextracted in a uniform manner from sky patrol data taken by the ROTSE-Itelescope. Extensive ROTSE-I light-curve data are combined with J-, H-,and K-band near-infrared data taken from the Two Micron All Sky Surveyto add color information. Contact binary candidates are selected usingthe observed period-color relation. Candidates are confirmed by visualexamination of the light curves. To enhance the utility of this catalog,we derive a new J-H period-color-luminosity relation and use this toestimate distances for the entire catalog. From these distance estimateswe derive an estimated contact binary space density of(1.7+/-0.6)×10-5 pc-3.
| New Minima of Selected Eclipsing Close Binaries
We present 180 CCD and photoelectric times of minima of selected closeeclipsing binaries.
| Physical Parameters of Components in Close Binary Systems. V
The paper presents combined spectroscopic and photometric orbitalsolutions for ten close binary systems: CN And, V776 Cas, FU Dra, UVLyn, BB Peg, V592 Per, OU Ser, EQ Tau, HN UMa and HT Vir. Thephotometric data consist of new multicolor light curves, while thespectroscopy has been recently obtained within the radial velocityprogram at the David Dunlap Observatory (DDO). Absolute parameters ofthe components for these binary systems are derived. Our results confirmthat CN And is not a contact system. Its configuration is semi-detachedwith the secondary component filling its Roche lobe. The configurationof nine other systems is contact. Three systems (V776 Cas, V592 Per andOU Ser) have high (44-77%) and six (FU Dra, UV Lyn, BB Peg, EQ Tau, HNUMa and HT Vir) low or intermediate (8-32%) fill-out factors. Theabsolute physical parameters are derived.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
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| Takýmyýldýz: | Ejderha |
| Sað Açýklýk: | 15h34m45.22s |
| Yükselim: | +62°16'44.2" |
| Görünürdeki Parlaklýk: | 10.485 |
| özdevim Sað Açýklýk: | -252.9 |
| özdevim Yükselim: | 13.2 |
| B-T magnitude: | 11.206 |
| V-T magnitude: | 10.545 |
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