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1.
We performed a multiwavelength study towards the infrared dark cloud(IRDC) G31.23+0.05 with new CO observations from Purple Mountain Observatory and archival data(the GLIMPSE,MIPSGAL,HERSCHEL,ATLASGAL,BGPS and NVSS surveys).From these observations,we identified three IRDCs with systemic velocities of 108.36 ± 0.06(cloud A),104.22 ± 0.11(cloud B) and75.73 ± 0.07 km s~(-1)(cloud C) in the line of sight towards IRDC G31.23.Analyses of the molecular and dust emission suggest that cloud A is a filamentary structure containing a young stellar object;clouds B and C both include a starless core.Clouds A and B are gravitationally bound and have a chance to form stars.In addition,the velocity information and the position-velocity diagram suggest that clouds A and B are adjacent in space and provide a clue hinting at a possible cloud-cloud collision.Additionally,the distribution of dust temperature shows a temperature bubble.The compact core in cloud A is associated with an UCHII region,an IRAS source,H_2O masers,CH_3OH masers and OH masers,suggesting that massive star formation is active there.We estimate the age of the HII region to be(0.03–0.09) Myr,indicating that the star inside is young.  相似文献   

2.
The discovery of silicate carbon star poses a challenge to the theory of stellar evolution in the late stage, hence it is important to look for more silicate carbon stars. To this end we have carried out cross-identifications between the new IRAS Low-Resolution Spectrum (LRS) database and the new carbon star catalog, CGCS3. We have found nine new silicate carbon stars with silicate features around 10μm and/or 18μm. These newly identified stars are located in the Regions IIIa and VII in the IRAS two-color diagram, which means they indeed have typical far infrared colors of silicate carbon stars. The infrared properties of each of these sources are discussed.  相似文献   

3.
We compare the performance of Bayesian Belief Networks (BBN), Multilayer Perception (MLP) networks and Alternating Decision Trees (ADtree) on separating quasars from stars with the database from the 2MASS and FIRST survey catalogs. Having a train- ing sample of sources of known object types, the classifiers are trained to separate quasars from stars. By the statistical properties of the sample, the features important for classifica- tion are selected. We compare the classification results with and without feature selection. Experiments show that the results with feature selection are better than those without feature selection. From the high accuracy found, it is concluded that these automated methods are robust and effective for classifying point sources. They may all be applied to large survey projects (e.g. selecting input catalogs) and for other astronomical issues, such as the parame- ter measurement of stars and the redshift estimation of galaxies and quasars.  相似文献   

4.
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   

5.
We present long term optical variability studies of bright X-ray sources in four nearby elliptical galaxies with the Chandra Advanced CCD Imaging Spectrometer array(ACIS-S) and observations from the Hubble Space Telescope(HST) Advanced Camera for Surveys.Out of the 46 bright(X-ray counts 60)sources that are in the common field of view of the Chandra and HST observations,34 of them have potential optical counterparts,while the rest of them are optically dark.After taking into account systematic errors,estimated using optical sources in the field as a reference,we find that four of the X-ray sources(three in NGC 1399 and one in NGC 1427) have variable optical counterparts at a high level of significance.The X-ray luminosities of these sources are ~ 10~(38) erg s~(-1) and are also variable on similar time scales.The optical variability implies that the optical emission is associated with the X-ray source itself rather than being the integrated light from a host globular cluster.For one source,the change in optical magnitude is 0.3,which is one of the highest reported for this class of X-ray sources and this suggests that the optical variability is induced by the X-ray activity.However,the optically variable sources in NGC 1399 have been reported to have blue colors(g- z 1).All four sources have been detected in the infrared(IR) by Spitzer as point sources,and their ratios of 5.8 to 3.6 μm flux are 0.63,indicating that their IR spectra are like those of Active Galactic Nuclei(AGNs).While spectroscopic confirmation is required,it is likely that all four sources are background AGNs.We find none of the X-ray sources having optical/IR colors different from AGNs to be optically variable.  相似文献   

6.
Radio stars have attracted astronomers' attention for several decades. To better understand the physics behind stellar radio emissions, it is important to study their optical behaviors. The LAMOST survey provides a large database for researching stellar spectroscopic properties of radio stars. In this work, we concentrate on their spectroscopic properties and infer physical properties from their spectra,such as stellar activity and variability. We mined big data from the LAMOST spectral survey Data Release 2(DR2), published on 2016 June 30, by cross-matching them with radio stars from FIRST and other surveys. We obtained 783 good stellar spectra with high signal to noise ratio for 659 stars. The criteria for selection were positional coincidence within 1.5′′and LAMOST objects classified as stars.We calculated the equivalent widths(EWs) of the Ca II HK, Hδ, Hγ, Hβ, Hα and Ca II IRT lines by integrating the line profiles. Using the EWs of the Hα line, we detected 147 active stellar spectra of 89 objects having emissions above the Hα continuum. There were also 36 objects with repeated spectra,28 of which showed chromospheric activity variability. Furthermore, we found 14 radio stars emitting noticeably in the Ca II IRT lines. The low value of the EW8542/EW8498 ratio for these 14 radio stars possibly alludes to chromospheric plage regions.  相似文献   

7.
The first mapping observations of the bipolar HII region S106 in HCN J = 3 - 2 line were made by KOSMA submillimeter telescope in April, 2004. The results show that there is a bipolar outflow centered on the high-mass star S106 IRS4 and that the flat structure of molecular cloud core is perpendicular to the axis of the outflow. This image roughly corresponds to the optical image where a dark lane bisects the bipolar HII region. Together with the optical, infrared and radio data, we conclude that the central UC HII region and molecular outflow formed before the  相似文献   

8.
Infrared Characteristics of Associated Sources of Water Masers   总被引：2，自引：0，他引：2  
We present an analysis of the infrared properties of 1417 water masers collected from the literature published by December 2004. The associated infrared sources of the water masers were identified with IRAS and MSX (Midcourse Space Experiment) catalogues. There are 1252 water masers associated with IRAS sources within 1', which include 700 interstellar and 552 stellar sources. For 382 sources, the IRAS counterpart identification and the maser classification are new. We found the colors of the interstellar maser sources are much redder than those of the stellar ones at IRAS wavelength bands; 99% of the interstellar maser sources are above black body line, while 95% of the stellar masers are below. The distribution difference of the two kinds of masers shown in the color-color diagram is due to their different optical depths and temperature distributions of dust regions. There are 743 water masers with MSX counterparts, of which 552 are interstellar masers and 191 are stellar masers. MSX colors of the associated sources of water masers are here analyzed for the first time. The color differences among the MSX bands are small and the interstellar masers are redder than the stellar masers. There is a correlation between the intensity of the stellar water maser emission and that of the 12μm and 25μm emissions, while there is no correlation between the water maser emission and the 8 μm emission. The infrared intensity increases with increasing wavelength for the interstellar masers, while it is the opposite for stellar masers. These results may provide clues for the pumping of water maser and for the properties of the two kinds of maser emission regions.  相似文献   

9.
The property of dark energy and the physical reason for the acceleration of the present universe are two of the most difficult problems in modern cosmology. The dark energy contributes about two-thirds of the critical density of the present universe from the observations of type-la supemovae (SNe Ia) and anisotropy of cosmic microwave background (CMB). The SN Ia observations also suggest that the universe expanded from a deceleration to an acceleration phase at some redshift, implying the existence of a nearly uniform component of dark energy with negative pressure. We use the "Gold" sample containing 157 SNe Ia and two recent well-measured additions, SNe Ia 1994ae and 1998aq to explore the properties of dark energy and the transition redshift. For a flat universe with the cosmological constant, we measureΩM = 0.28-0.05 0.04, which is consistent with Riess et al. The transition redshift is ZT = 0.60-0.08 0.06. We also discuss several dark energy models that define w(z) of the parameterized equation of state of dark energy including one parameter and two parameters (w(z) being the ratio of the pressure to energy density). Our calculations show that the accurately calculated transition redshift varies from ZT = 0.29-0.06 0.07 to zT = 0.60-0.08 0.06 across these models. We also calculate the minimum redshift zc at which the current observations need the universe to accelerate.  相似文献   

10.
We report our detailed data analysis of 39 γ-ray sources selected from the 992 unassociated sources in the third Fermi Large Area Telescope Third Source Catalog.The selection criteria,which were set for finding candidate millisecond pulsars(MSPs),are non-variables with curved spectra and 5?Galactic latitudes.From our analysis,24 sources were found to be point-like sources not contaminated by background or nearby unknown sources.Three of them,J1544.6-1125,J1625.1-0021 and J1653.6-0158,have been previously studied,indicating that they are likely MSPs.The spectra of J0318.1+0252 and J2053.9+2922 do not have properties similar to known γ-ray MSPs,and we thus suggest that they are not MSPs.Analysis of archival X-ray data for most of the 24 sources was also conducted.Four sources were found with X-ray objects in their error circles,and 16 with no detection.The ratios between the γ-ray fluxes and X-ray fluxes or flux upper limits are generally lower than those of known γ-ray MSPs,suggesting that if the γ-ray sources are MSPs,none of the X-ray objects are their counterparts.Deep X-ray or radio observations of these sources are needed in order to identify their MSP nature.  相似文献   

11.
The equations of state for degenerate electron and neutron gases are studied in the presence of magnetic fields. After including quantum effects in the investigation of the structural properties of these systems, it is found that some hypermagnetized stars can be unstable according to the criterion of stability of pressures. Highly magnetized white dwarfs should collapse producing a supernova type Ia, while superstrong magnetized neutron stars cannot stand their own magnetic field and must implode, too. A comparison of our results with a set of the available observational data of some compact stars is also presented, and the agreement between this theory and observations is verified.  相似文献   

12.
We conducted photometric and spectroscopic observations of Ross 15 in order to further study the flare properties of this less observed flare star.A total of 28 B-band flares are detected in 128 hr of photometric observations,leading to a total flare rate of 0.22-0.040.04 h-1,more accurate than that provided by previous work.We give the energy range of the B-band flare(1029.5-1031.5 erg) and the flare frequency distribution(FFD) for the star.Within the same energy range,the FFD is lower than that of GJ 1243(M4)and YZ CMi(M4.5),roughly in the middle of those of three M5-type stars and higher than the average FFDs of spectral types> M6.We performed,for the first time for Ross 15,simultaneous high-cadence spectroscopic and photometric observations,resulting in detection of the most energetic flare in our sample.The intensity enhancements of the continuum and Balmer lines with significant correlations between them are detected during the flare,which is the same as those of other deeply studied flare stars with similar spectral type.  相似文献   

13.
We compiled a catalog of Faraday rotation measures(RMs) for 4553 extragalactic radio point sources published in literature. These RMs were derived from multi-frequency polarization observations. The RM data are compared to those in the NRAO VLA Sky Survey(NVSS) RM catalog. We reveal a systematic uncertainty of about 10.0 ± 1.5 rad m-2in the NVSS RM catalog. The Galactic foreground RM is calculated through a weighted averaging method by using the compiled RM catalog together with the NVSS RM catalog,with careful consideration of uncertainties in the RM data. The data from the catalog and the interface for the Galactic foreground RM calculations are publicly available on the webpage: http://zmtt.bao.ac.cn/RM/.  相似文献   

14.
On the basis of the properties of known γ-ray millisecond pulsars(MSPs), we have selected 77un-associated sources from the Fermi Large Area Telescope(LAT) third source catalog for the purpose of finding likely candidate MSPs. Previously, detailed LAT data analysis for 39 of them was reported,and here we report the analysis for the remaining 38 sources. We identify that among the 38 sources, 28 of them are single point-like sources with clean background and their spectra show significant curvature.We also conduct an analysis of archival X-ray data available for 24 of the 28 sources. In the fields of10 sources, there is at least one X-ray object, and in those of the other 14 sources, no X-ray object is detected but this is probably due to the X-ray observations being short. We discuss the possible MSP nature for these sources. Six of them(J0514.6-4406, J1035.7-6720, J1624.2-4041, J1744.1-7619,J1946.4-5403 and J2039.6-5618) are most likely associated with pulsars because of multi-wavelength identifications including direct radio or γ-ray detection of pulsations. To firmly establish the associations or verify the MSP nature for other sources, deep X-ray and/or optical observations are needed.  相似文献   

15.
Near-infrared images and K-band spectroscopy of the massive star-forming region IRAS 23151+5912 are presented. The JHK' images reveal an embed-ded infrared cluster associated with infrared nebula, and the H_2 (2.12μm) narrow-band image provides for the first time evidence of outflow activity associated withthe cluster. That the cluster is young can be shown by the high percentage ofinfrared excess sources and the outflow activity. We suggest an age of the clus-ter of ～ 10~6yr. Eight young stars are found in the bright nebular core aroundIRAS 23151+5912. By the color-magnitude diagrams of the cluster, we found fivehigh--mass YSOs and four intermediate-mass YSOs in the cluster. Eight H_2 emissionfeatures are discovered in the region with a scattered and non-axisymmetric distri-bution, indicating the existence of multiple outflows driven by the cluster. DiffuseH_2 emission detected to the north and to the west of the cluster may result fromUV leakage of the cluster. Brγ, H_2, and CIV emission lines are  相似文献   

16.
We calculate the properties of static strange stars using a quark model with chiral mass scaling.The results are characterized by a large maximum mass (～ 1.6 M) and radius (～10 km).Together with a broad collection of modern neutron star models,we discuss some recent astrophysical observational data that could shed new light on the possible presence of strange quark matter in compact stars.We conclude that none of the present astrophysical observations can prove or confute the existence of strange stars.  相似文献   

17.
Learning Vector Quantization for Classifying Astronomical Objects   总被引：2，自引：0，他引：2  
The sizes of astronomical surveys in different wavebands are increasing rapidly. Therefore, automatic classification of objects is becoming ever more important. We explore the performance of learning vector quantization (LVQ) in classifying multi-wavelength data. Our analysis concentrates on separating active sources from non-active ones. Different classes of X-ray emitters populate distinct regions of a multidimensional parameter space. In order to explore the distribution of various objects in a multidimensional parameter space, we positionally cross-correlate the data of quasars, BL Lacs, active galaxies, stars and normal galaxies in the optical, X-ray and infrared bands. We then apply LVQ to classify them with the obtained data. Our results show that LVQ is an effective method for separating AGNs from stars and normal galaxies with multi-wavelength data.  相似文献   

18.
We investigate the masses of glitching pulsars in order to constrain their equation of state(EOS). The observations of glitches(sudden jumps in rotational frequency) may provide information on the interior physics of neutron stars. With the assumption that glitches are triggered by superfluid neutrons, the masses of glitching neutron stars can be estimated using observations of maximum glitches.Together with the observations of thermal emission from glitching pulsars Vela and J1709–4429, the slope of symmetry energy and incompressibility of nuclear matter at saturation density can be constrained.The slope of symmetry energy L should be larger than 67 MeV while the lower limit of incompressibility for symmetric nuclear matter K_0 is 215 MeV. We also obtain a relationship between L and K_0:6.173 MeV + 0.283 K_0≤ L ≤ 7.729 MeV + 0.291 K_0. The restricted EOSs are consistent with the observations of 2-solar-mass neutron stars and gravitational waves from a binary neutron star inspiral.  相似文献   

19.
Active galactic nuclei(AGNs) can be divided into two major classes,namely radio-loud and radio-quiet AGNs.A small subset of the radio-loud AGNs is called blazars,which are believed to be unified with Fanaroff-Riley type Ⅰ and type Ⅱ(FRIⅡ) radio galaxies.Following our previous work,we present a latest sample of 966 sources with measured radio flux densities of the core and extended components.The sample includes 83 BL Lacs,473 flat spectrum radio quasars,101 Seyferts,245 galaxies,52 FRIsⅡs and12 unidentified sources.We then calculate the radio core-dominance parameters and spectral indices and study their relationship.Our analysis shows that the core-dominance parameters and spectral indices are quite different for different types of sources.We also confirm that the correlation between core-dominance parameter and radio spectral index extends over all the sources in a large sample presented.  相似文献   

20.
As we now know, there are at least two major difficulties with general rel- ativity （GR）. The first one is related to its incompatibility with quantum mechanics, in the absence of a consistent, widely accepted theory that combines the two theo- ries. The second problem is related to the requirement of the dark sectors-inflaton, dark matter and dark energy by the energy-stress tensor, which are needed to explain a variety of astronomical and cosmological observations. Research has indicated that the dark sectors themselves do not have any non-gravitational or laboratory evidence. Moreover, the dark energy poses, in addition, a serious confrontation between funda- mental physics and cosmology. Guided by theoretical and observational evidences, we are led to an idea that the source of gravitation and its manifestation in GR should be modified. The result is in striking agreement with not only the theory, but also the ob- servations, without requiring the dark sectors of the standard approach. Additionally, it provides natural explanations to some unexplained puzzles.  相似文献   

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