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1.
We carried out observations toward the giant molecular cloud W 37 with the J = 1- 0 transitions of~(12) CO,~(13)CO and C~(18)O using the 13.7 m single-dish telescope at the Delingha station of Purple Mountain Observatory. Based on these CO lines, we calculated the column densities and cloud masses for molecular clouds with radial velocities around +20 km s~(-1). The gas mass of W 37, calculated from~(13)CO emission,is 1.7 × 10~5M⊙, above the criterion to be considered a giant molecular cloud. The dense ridge of W 37 is a dense filament, which is supercritical in terms of linear mass ratio. Dense clumps found by C~(18)O emission are aligned along the dense ridge at regular intervals of about 2.8 pc, similar to the clump separation caused by large-scale ‘sausage instability'. We confirm the identification of the giant molecular filament(GMF)G 18.0–16.8 and find a new giant filament, G 16.5–15.8, located ~ 0.7?to the west of G 18.0–16.8. Both GMFs are not gravitationally bound, as indicated by their low linear mass ratio(~ 80 Mpc~(-1)⊙). We compared the gas temperature map with the dust temperature map from Herschel images, and found similar structures. The spatial distributions of class I objects and the dense clumps are reminiscent of triggered star formation occurring in the northwestern part of W 37, which is close to NGC 6611.  相似文献   

2.
We present results of a high resolution study of the filamentary infrared dark cloud G192.76+00.10 in the S254-S258 OB complex in several molecular species tracing different physical conditions. These include three isotopologues of carbon monoxide(CO), ammonia(NH3) and carbon monosulfide(CS). The aim of this work is to study the general structure and kinematics of the filamentary cloud, and its fragmentation and physical parameters. The gas temperature is derived from the NH3(J, K) =(1,1),(2, 2) and ~(12)CO(2-1) lines, and the ~(13)CO(1-0), ~(13)CO(2-1) emission is used to investigate the overall gas distribution and kinematics. Several dense clumps are identified from the CS(2-1)data. Values of the gas temperature lie in the range 10-35 K, and column density N(H2) reaches the value 5.1 x 10~(22) cm~(-2). The width of the filament is of order 1 pc. The masses of the dense clumps range from ～ 30 M_☉ to ～ 160 M_☉. They appear to be gravitationally unstable. The molecular emission shows a gas dynamical coherence along the filament. The velocity pattern may indicate longitudinal collapse.  相似文献   

3.
We identify 225 filaments from an H_2 column density map constructed using simultaneous ~(12)CO,~(13)CO and C~(18)O(J=1-0) observations carried out as a part of the Milky Way Imaging Scroll Painting(MWISP) project.We select 46 long filaments with lengths above 1.2 pc to analyze the filament column density profiles.We divide the selected filaments into 397 segments and calculate the column density profiles for each segment.The symmetries of the profiles are investigated.The proportion of intrinsically asymmetrical segments is 65.3%,and that of intrinsically symmetrical ones is 21.4%.The typical full width at half maximum(FWHM) of the intrinsically symmetrical filament segments is ～ 0.67 pc with the Plummer-like fitting,and ～ 0.50 pc with the Gaussian fitting,respectively.The median FWHMs derived from the second-moment method for intrinsically symmetrical and asymmetrical profiles are ～ 0.44 and 0.46 pc,respectively.Close association exists between the filamentary structures and the YSOs in the region.  相似文献   

4.
BH Cen is a short-period early-type binary with a period of 0.792 din the extremely young star-forming cluster IC 2944. New multi-color CCD photometric light curves in U, B, V, R and I bands are presented and are analyzed by using the Wilson-Devinney code. It is detected that BH Cen is a high-mass-ratio overcontact binary with a fill-out factor of 46.4% and a mass ratio of 0.89. The derived orbital inclination i is 88.9 degrees, indicating that it is a totally eclipsing binary and the photometric parameters can be determined reliably. By adding new eclipse times, the orbital period changes in the binary are analyzed. It is confirmed that the period of BH Cen shows a long-term increase while it undergoes a cyclic oscillation with an amplitude of A_3 = 0.024 d and a period of P_3 = 50.3 yr. The high mass ratio, overcontact configuration and long-term continuous increase in the orbital period all suggest that BH Cen is in the evolutionary state after the shortest-period stage of Case A mass transfer.The continuous increase in period can be explained by mass transfer from the secondary component to the primary one at a rate of˙M_2 = 2.8×10~(-6) M_⊙per year. The cyclic change can be plausibly explained by the presence of a third body because both components in the BH Cen system are early-type stars. Its mass is determined to be no less than 2.2 M_⊙at an orbital separation of about 32.5 AU. Since no third light was found during the photometric solution, it is possible that the third body may be a candidate for a compact object.  相似文献   

5.
Type Ia supernovae(SNe Ia) are believed to be thermonuclear explosions of carbon oxygen(CO) white dwarfs(WDs) with masses close to the Chandrasekhar mass limit. How a CO WD accretes matter and grows in mass to this limit is not well understood, hindering our understanding of SN Ia explosions and the reliability of using SNe Ia as a cosmological distance indicator. In this work, we employed the stellar evolution code MESA to simulate the accretion process of hydrogen-rich material onto a 1.0 M_⊙CO WD at a high rate(over the Eddington limit) of 4.3 × 10~(-7) M_⊙yr~(-1). The simulation demonstrates the characteristics of the double shell burning on top of the WD, with a hydrogen shell burning on top of a helium burning shell. The results show that helium shell burning is not steady(i.e.it flashes). Flashes from the helium shell are weaker than those in the case of accretion of helium-rich material onto a CO WD. The carbon to oxygen mass ratio resulting from the helium shell burning is higher than what was previously thought. Interestingly, the CO WD growing due to accretion has an outer part containing a small fraction of helium in addition to carbon and oxygen. The flashes become weaker and weaker as the accretion continues.  相似文献   

6.
Based on MaNGA integral field unit(IFU) spectroscopy we search 60 AGN candidates,which have stellar masses M_*≤5 × 10~9 M_⊙ and show AGN ionization signatures in the BPT diagram.For these AGN candidates,we derive the spatially resolved stellar population with the stellar population synthesis code STARLIGHT and measure the gradients of the mean stellar age and metallicity.We find that the gradients of mean stellar age(metallicity) of individual AGN-host dwarfs are diverse in 0-0.5 Re,0.5-1 Re and 0-1 Re.However,the overall behavior of the mean stellar age(metallicity) profiles tend to be flat,as the median values of the gradients are close to zero.We further study the overall behavior of the mean stellar age(metallicity) by plotting the co-added radial profiles for the AGN sample and compare with a control sample with similar stellar mass.We find that the median values of light-weighted mean stellar ages of the AGN sample are as old as 2-3 Gyr within 2 Re,which are about 4-7 times older than those of the control sample.Meanwhile,most of the AGN candidates are low-level AGNs,as only eight sources have L_([O)_(Ⅲ])10~(39.5) erg s~(-1).Hence,the AGNs in dwarf galaxies might accelerate the evolution of galaxies by accelerating the consumption of the gas,resulting in an overall quenching of the dwarf galaxies,and the AGNs also become weak due to the lack of gas.The median values of mass-weighted mean stellar age of both samples within 2 Re are similar and as old as about 10 Gyr,indicating that the stellar mass is mainly contributed by old stellar populations.The gradients of co-added mean stellar metallicity for both samples tend to be negative but close to zero,and the similar mean stellar metallicity profiles for both samples indicate that the chemical evolution of the host galaxy is not strongly influenced by the AGN.  相似文献   

7.
The emerging massive binary system associated with AFGL 961 signifies the latest generation of massive star and cluster formation in the Rosette Molecular Complex. We present the detection of a compact cluster of dusty cores toward the AFGL 961 region based on continuum imaging at 1.3 mm by the Submillimeter Array. The binary components of AFGL 961 are associated with the most intensive millimeter emission cores or envelopes, confirming that they are indeed in an early stage of evolution. The other massive cores, however, are found to congregate in the close vicinity of the central high-mass protostellar binary. They have no apparent infrared counterparts and are, in particular, well aligned transverse to the bipolar molecular outflows originating from AFGL 961. This provides evidence for a likely triggered origin of the massive cores. All 40 individual cores with masses ranging between 0.6 and 15 M⊙ were detected above a 3 σ level of 3.6 mJy beam-1 (or0.4 M⊙ ), based on which we derive a total core mass of 107 M⊙ in the AFGL 961 region. As compared to the stellar initial mass function, a shallow slope of 1.8 is, however, derived from the best fit to the mass spectrum of the millimeter cores with a prestellar and/or protostellar origin. The flatter core mass distribution in the AFGL 961 region is attributed here to dynamic perturbations from the massive molecular outflows that originated from the massive protostellar binary, which may have altered the otherwise more quiescent conditions of core or star formation, enhanced the formation of more massive cores and, as a result, influenced the core mass distribution in its close vicinity.  相似文献   

8.
We present a multi-transition study to investigate the physical properties of dust and molecular gas in the archetypical merger Arp 299 by using data including James Clerk Maxwell Telescope(JCMT)850 and 450 μm observations, Herschel 500, 350, 250, 160 and 70 μm continuum maps, as well as the CO(3–2), CO(4–3) low-J CO lines and CO(11–10), CO(13–12), CO(14–13) high-J CO lines. The CO(3–2) and CO(4–3) lines are observed by JCMT, and the CO(11–10), CO(13–12), CO(14–13) lines are available on the Herschel Science Archive. The resolution of the Herschel Spectral and Photometric Imaging Receiver(SPIRE) Fourier transform spectrometer(FTS) CO(11–10) data is similar to that of the JCMT CO(3–2) line, while the resolution of the SPIRE/FTS CO(13–12) and Photodetector Array Camera and Spectrometer(PACS) CO(14–13) data is similar to that of JCMT CO(4–3), allowing us to obtain accurate line ratios of I_(CO(11-10))/I_(CO(3-2)), I_(CO(13-12))/I_(CO(4-3))and I_(CO(14-13))/I_(CO(4-3)).By modeling the spectral energy distribution of the continuum data, we conclude that two components(cold and warm) exist in the dust, with the warm component occupying a small percent of the total dust mass. We further use a radiative transfer analysis code, RADEX, to calculate the density, temperature and column density of warm gas in the central region, which shows that the kinetic temperature Tkinis in the range 110 to 150 K and hydrogen density n(H_2) is in the range 10~(4.7)-10~(5.5)cm~(-3). We show that the hot dust is located in the central region of IC 694 with a radius of ~ 4′′and estimate that the warm gas mass is in the range 3.8 × 10~7M_⊙ to 7.7 × 10~7M_⊙, which contains 5.0%–15.0% of the total H_2 mass for the region of IC 694. We also calculate the star formation rate of the galaxy in particular,which is much higher than that of the Milky Way.  相似文献   

9.
We observed the line-of-sight magnetic field in the chromosphereand photosphere of a large quiescent filament on the solar disk on September 6, 2001 using the Solar Magnetic Field Telescope in Huairou Solar Observing Station. The chromospheric and photospheric magnetograms together with Hβ filtergrams of the filament were examined. The filament was located on the neutral line of the large scale longitudinal magnetic field in the photosphere and the chromosphere. The lateral feet of the filament were found to be related to magnetic structures with opposite polarities. Two small lateral feet are linked to weak parasitic polarity. There is a negative magnetic structure in the photosphere under a break of the filament. At the location corresponding to the filament in the chromospheric magnetograms, the magnetic strength is found to be about 40-70 Gauss (measuring error about 39 Gauss). The magnetic signal indicates the amplitude and orientation of the internal magnetic field in the filament. We discuss several possible causes which may produce such a measured signal. A twisted magnetic configuration inside the filament is suggested .  相似文献   

10.
New multi-color photometric observations of the previously unstudied contact binary QW Gem are presented. Completely covered BVRI band light curves were obtained, including four new times of light minima. The light curves were simultaneously analyzed with the 2013 version of the Wilson-Devinney method, assuming a third light. The photometric solutions confirm that QW Gem is a W-type W UMa system with a fill-out factor of f~17%. The absolute parameters of the components were determined to be M_p= 1.33 ± 0.03 M_☉,M_s = 0.44 ± 0.01 M_☉,R_p = 1.25 ± 0.01 R_☉,R_s = 0.77 ± 0.01 R_☉,Lp= 1.68 ± 0.03 L_☉ and L_s = 0.68 ± 0.01 L_☉. The orbital period change of QW Gem was investigated by the O-C method using all available data. The results show that this binary system could have undergone a continuous orbital period decrease during the past two decades at a rate of about dP/dt =-2.55 × 10~(-7) d yr~(-1). In addition, a small-amplitude oscillation was detected to be superimposed on a long-term decrease.  相似文献   

11.
Photometric observations of AH Cnc,a W UMa-type system in the open cluster M67,were carried out by using the 50 BiN telescope.About 100 h of time-series B- and V-band data were taken,based on which eight new times of light minima were determined.By applying the Wilson-Devinney method,the light curves were modeled and a revised photometric solution of the binary system was derived.We confirmed that AH Cnc is a deep contact(f= 51%),low mass-ratio(q = 0.156) system.Adopting the distance modulus derived from study of the host cluster,we have re-calculated the physical parameters of the binary system,namely the masses and radii.The masses and radii of the two components were estimated to be respectively 1.188(±0.061) M_☉,1.332(±0.063) R_☉ for the primary component and 0.185(±0.032) M_☉,0.592(±0.051) R_☉ for the secondary.By adding the newly derived minimum timings to all the available data,the period variations of AH Cnc were studied.This shows that the orbital period of the binary is continuously increasing at a rate of dp/dt = 4.29×10~(-10)dyr~(-1).In addition to the long-term period increase,a cyclic variation with a period of 35.26 yr was determined,which could be attributed to an unresolved tertiary component of the system.  相似文献   

12.
We present the first photometric analysis of three totally-eclipsing W UMa binaries,NS VS2443858,NSVS 780649 and V1098 Her.The absolute astrophysical parameters of the stellar components were determined by means of Gaia distances and light curve solutions.The results show that:(ⅰ) Two of the systems,NSVS 2443858 and V1098 Her,are of A subtype while the obtained temperature of the secondary component of NSVS 780649 indicates that it is a W-subtype system;(ⅱ) The estimated mass ratios approach the lower limit of the mass ratio assumed by researchers in recent years so our targets could be classified as extreme mass ratio binary(EMRB) systems;(ⅲ) All the systems have deep contact configurations,so they also are deep low mass ratio(DLMR) systems;(ⅳ) The components of our systems are stars of F and G spectral type and undergo total eclipses;(ⅴ) The sum 0.871 M_⊙ of the component masses of NSVS 780649 is below the mass limit of 1.0-1.2 M_⊙ assumed for the known contact binary stars.  相似文献   

13.
Thirty massive clumps associated with bright infrared sources were observed to detect the infall signatures and characterize infall properties in the envelope of the massive clumps by APEX telescope in CO(4-3)and C17O(3-2)lines.Eighteen objects exhibit a"blue profile"in the CO(4-3)line with virial parameters less than 2,suggesting that global collapse is taking place in these massive clumps.The CO(4-3)lines were fitted via the two-layer model in order to obtain infall velocities and mass infall rates.Derived mass infall rates range from 10-3 to 10-1 M☉yr*(-1).A positive relationship between clump mass and infall rate appears to indicate that gravity plays a dominant role in the collapsing process.Higher luminosity clumps have a larger mass infall rate,implying that those clumps with higher mass infall rates possess a higher star formation rate.  相似文献   

14.
New light curves and photometric solutions of FP Lyn, FV CVn and V354 UMa are presented.We found that these three systems are W-subtype shallow contact binaries. In addition, it is obvious that the light curves of FP Lyn and V354 UMa are asymmetric. Therefore, a hot spot was added on the primary star of FP Lyn and a dark spot was added on the secondary star of V354 UMa. At the same time, we added a third light to the photometric solution of FP Lyn for the final result. The obtained mass ratios and fill-out factors are q = 1.153 and f = 13.4% for FP Lyn, q = 1.075 and f = 4.6% for FV CVn, and q = 3.623 and f = 10.7% for V354 UMa respectively. The investigations of orbital period for these three systems indicate that the periods are variable. FP Lyn and V354 UMa were discovered to have secularly increasing components with rates of dp/dt = 4.19 × 10~(-7) d yr~(-1) and dp/dt = 7.70 × 10~(-7) d yr~(-1) respectively,which are feasibly caused by conservative mass transfer from the less massive component to the more massive component. In addition, some variable components were discovered for FV CVn, including a rate of dp/dt =~(-1).13 × 10~(-6) d yr~(-1) accompanied by a cyclic oscillation with amplitude and period of 0.0069 d and 10.65 yr respectively. The most likely explanation for the long-term decrease is angular momentum loss.The existence of an additional star is the most plausible explanation for the periodic variation.  相似文献   

15.
We carry out a re-analysis of the photometric data in R_cI_c bands which were taken during the Nainital Microlensing Survey from 1998 to 2002 with the aim to detect gravitational microlensing events in the direction of M31. Here, we do photometric analysis of a faint W UMa binary CSS_J004259.3 +410629 identified in the target field. The orbital period of this star is found to be 0.266402±0.000018 d.The photometric mass ratio, q,is found to be 0.28 ± 0.01. The photometric light curves are investigated using the Wilson-Devinney(WD) code and absolute parameters are determined using empirical relations which provide masses and radii of the binary as M_1 = 1.19 ± 0.09 M_☉,M_2 = 0.33 ± 0.02 M_⊙ and R_1=1.02±0.04 R_⊙,R_2 = 0.58 ±0.08 R_⊙ respectively based on R_c band data. Quite similar values are found by analyzing I_c band data. From the photometric light curve examination, the star is understood to be a low mass-ratio overcontact binary of A-subtype with a high fill-out factor of about 47%. The binary system is found to be located approximately at a distance of 2.64 ± 0.03 kpc having a separation of 2.01 ± 0.05 R_⊙ between the two components.  相似文献   

16.
We apply the jet-powered ILOT scenario to two recently studied intermediate luminosity optical transients(ILOTs),and find the relevant shell mass and jets' energy that might account for the outbursts of these ILOTs.In the jet-powered ILOT scenario,an accretion disk around one of the stars of a binary system launches jets.The interaction of the jets with a previously ejected slow shell converts kinetic energy to thermal energy,part of which is radiated away.We apply two models of the jet-powered ILOT scenario.In the spherical shell model,the jets accelerate a spherical shell,while in the cocoon toy model the jets penetrate into the shell and inflate hot bubbles,the cocoons.We find consistent results.For the ILOT(ILRT:intermediate luminosity red transient) SNhunt120 we find the shell mass and jets' energy to be Ms■0.5-1 M_☉ and E_(2 j)■5×10~(47) erg,respectively.The jets' half opening angle is α_j■30°-60°.For the second peak of the ILOT(luminous red nova) AT 2014 ej we find these quantities to be M_s1-2 M_☉ and E_(2 j)1.5×10~(48) erg,with αj■20°-30°.The models cannot tell whether these ILOTs were powered by a stellar merger that leaves one star,or by mass transfer where both stars survived.In both cases the masses of the shells and energies of the jets suggest that the binary progenitor system was massive,with a combined mass of M_1+M_210 ■M_☉.  相似文献   

17.
We present radio images of NRAO 530 on scales ranging from pc to kpc. The observations include the EVN at 5 GHz, the VLBA at 1.6, 8.6 and 15 GHz, the MERLIN at 1.6 and 5 GHz, and the VLA at 5, 8.4, 15, 22, and 43 GHz. The VLBI images show a core-jet structure with an oscillating trajectory on a scale of about 30 mas north of the strongest compact component (core). Superluminal motions are detected in five of the jet compo-nents with apparent velocities in the range of 13.6 to 25.2c. A new component is detected at 15 GHz with the VLBA observations, which appears to be associated with the outburst in 2002. Significant polarized emission is detected around the core with the VLBA observationsat 15 GHz. Rapid variations of the polarization intensity and angle are found between the epochs in 2002 and 2004. On the kpc-scale, a distant component (labelled as WL) located 11 arcsec west (PA=-86°) of the core is detected beyond the core-jet structure which ex-tended to several hundreds of mas in the north-west direction (-50°). A significant emission between the core-jet structure and the WL is revealed. A clump of diffuse emission (labelled EL, 12 arcsec long) at PA 70° to the core, is also detected in the VLA observations, suggest-ing the presence of double lobes in the source. The core component shows a flat spectrum,while the distant components WL and EL have steep spectra. The steep spectra of the distantcomponents and the detection of the arched emission suggest that the distant components are lobes or hot-spots powered by the core of NRAO 530. The morphologies from pc-to kpc- scales and the bending of jets are investigated. The observed radio morphology from pc to kcp appears to favor the model in which precession or wobbling of the nuclear disk drives the helical motion of the radio plasma and produces the S-shaped structure on kpc scale.  相似文献   

18.
A filament is a cool, dense structure suspended in the solar corona. The eruption of a filament is often associated with a coronal mass ejection(CME), which has an adverse effect on space weather. Hence,research on filaments has attracted much attention in the recent past. The tilt angle of active region(AR)magnetic bipoles is a crucial parameter in the context of the solar dynamo, which governs the conversion efficiency of the toroidal magnetic field to poloidal magnetic field. Filaments always form over polarity inversion lines(PILs), so the study of tilt angles for these filaments can provide valuable information about generation of a magnetic field in the Sun. We investigate the tilt angles of filaments and other properties using McIntosh Archive data. We fit a straight line to each filament to estimate its tilt angle. We examine the variation of mean tilt angle with time. The latitude distribution of positive tilt angle filaments and negative tilt angle filaments reveals that there is a dominance of positive tilt angle filaments in the southern hemisphere and negative tilt angle filaments dominate in the northern hemisphere. We study the variation of the mean tilt angle for low and high latitudes separately. Investigations of temporal variation with filament number indicate that total filament number and low latitude filament number vary cyclically, in phase with the solar cycle. There are fewer filaments at high latitudes and they also show a cyclic pattern in temporal variation. We also study the north-south asymmetry of filaments with different latitude criteria.  相似文献   

19.
The local standard of rest(LSR) provides a reference framework for studies of Galactic kinematics. Determination of the LSR corresponds to the measurement of solar peculiar motion, which is under debate due to the fact that different methods and samples have been used. Adopting the astrometric data and line-of-sight velocities of main sequence stars from Gaia DR2, we present a detailed analytical study of stellar kinematics in the solar neighborhood. Based on an improved version of the Stromberg relation, we obtain a robust estimation of the solar peculiar motion, which is given by(U☉,V☉,W☉)=(8.63 ± 0.64, 4.76 ± 0.49, 7.26 ± 0.36) km s-1. The corresponding radial scalelength is yielded as Rd ～ 2.5 kpc. The radial and vertical components of solar peculiar motion are basically consistent with the classical values, while the tangential component is a few km s-1 smaller than most estimates in literature.  相似文献   

20.
Multi-color light curves of V1197 Her were obtained with the 2.4 meter optical telescope at the Thai National Observatory and the Wilson-Devinney(W-D) program was used to model the observational light curves. The photometric solutions reveal that V1197 Her is a W-subtype shallow contact binary system with a mass ratio of q = 2.61 and a fill-out factor of f = 15.7%. The temperature difference between the primary star and secondary star is only 140 K in spite of the low degree of contact, which means that V1197 Her is not only in geometrical contact configuration but is also already under thermal contact status.The orbital inclination of V1197 Her is as high as i = 82.7?, and the primary star is completely eclipsed at the primary minimum. The totally eclipsing characteristic implies that the determined physical parameters are highly reliable. The masses, radii and luminosities of the primary star(star 1) and secondary star(star2) are estimated to be M1 = 0.30(1) M_⊙, M2 = 0.77(2) M_⊙, R1 = 0.54(1) R_⊙, R2 = 0.83(1) R_⊙,L1 = 0.18(1) L_⊙and L2 = 0.38(1) L_⊙. The evolutionary statuses of the two component stars are drawn in the Hertzsprung-Russell diagram, showing that the less massive but hotter primary star is more evolved than the secondary star. The period of V1197 Her is decreasing continuously at a rate of d P/dt =-2.58 ×10-7 day · year-1, which can be explained by mass transfer from the more massive star to the less massive one at a rate of dM_2/dt=-1.61 × 10~(-7) M_⊙year~(-1). The light curves of V1197 Her are reported to show the O'Connell effect. Thus, a cool spot is added to the more massive star to model the asymmetry in the light curves.  相似文献   

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