Using long-term optical, ultraviolet(UV) and X-ray data, we present a study of a classical T Tauri star CV Cha. The V-band light curve obtained from the All Sky Automated Survey(ASAS) shows short as well as long-term ...Using long-term optical, ultraviolet(UV) and X-ray data, we present a study of a classical T Tauri star CV Cha. The V-band light curve obtained from the All Sky Automated Survey(ASAS) shows short as well as long-term variability. The short-term variability could be due to rotational modulation of CV Cha. We derive the rotational period of 3.714 ± 0.001 d for CV Cha. UV light curves obtained from Swift also show the variations. X-ray light curves from XMM-Newton and Swift do not show any significant short as well as long-term variability. However, the light curve from Chandra appears to be variable, which could be due to the emergence of flaring activities. X-ray spectra from all observations are explained well by the single temperature plasma of 0.95 keV with X-ray luminosity of 1030.4erg s-1in the 0.5–7.5 keV energy band. It appears that variability in optical and UV bands could be due to the presence of both hot and cool spots on the surface, while X-ray emission is dominated by magnetic processes.展开更多
A high angular resolution near-infrared image that shows the intensity of polarization for the GG Tau A binary system was obtained with the Subaru Telescope. The image shows a circumbinary disk scattering the light fr...A high angular resolution near-infrared image that shows the intensity of polarization for the GG Tau A binary system was obtained with the Subaru Telescope. The image shows a circumbinary disk scattering the light from the central binary. The azimuthal profile of the intensity of polarization for the circumbinary disk is roughly reproduced by a simple disk model with the Henyey-Greenstein phase function and the Rayleigh function, indicating there are small dust grains at the surface of the disk. Combined with a previous observation of the circumbinary disk, our image indicates that the gap structure in the circumbinary disk orbits counterclockwise, but material in the disk orbits clockwise. We propose that there is a shadow caused by material located between the central binary and the circumbinary disk. The separations and position angles of the stellar components of the binary in the past 20 yr are consistent with the binary orbit with a = 33.4 AU and e = 0.34.展开更多
We report the results of optical spectroscopic monitoring observations of a T Tauri star, V409 Tau. A previous photometric study indicated that this star experienced dimming events due to the obscuration of light from...We report the results of optical spectroscopic monitoring observations of a T Tauri star, V409 Tau. A previous photometric study indicated that this star experienced dimming events due to the obscuration of light from the central star with a distorted circumstellar disk. We conducted medium-resolution (R ~10,000) spectroscopic observations with 2-m Nayuta telescope at Nishi-Harima Astronomical Observatory. Spectra were obtained in 18 nights between November 2015 and March 2016. Several absorption lines such as Ca I and Li, and the Hαemission line were confirmed in the spectra. The Ic-band magnitudes of V409 Tau changed by approximately 1 magnitude during the observation epoch. The equivalent widths of the five absorption lines are roughly constant despite changes in the Ic-band magnitudes. We conclude that the light variation of the star is caused by the obscuration of light from the central star with a distorted circumstellar disk, based on the relationship between the equivalent widths of the absorption lines and the Ic-band magnitudes. The blue component of the Hαemission line was dominant during the observation epoch, and an inverse P Cygni profile was observed in eight of the spectra. The time-variable inverse P Cygni profile of the Hαemission line indicates unsteady mass accretion from the circumstellar disk to the central star.展开更多
We present a comprehensive mid-infrared spectroscopic survey of 124 Herbig Ae/Be stars using newly processed Spitzer/IRS spectra from the newly released CASSISjuice database.Based on prominent dust and molecular signa...We present a comprehensive mid-infrared spectroscopic survey of 124 Herbig Ae/Be stars using newly processed Spitzer/IRS spectra from the newly released CASSISjuice database.Based on prominent dust and molecular signatures(polycyclic aromatic hydrocarbons(PAHs),silicates,and hydrogenated amorphous carbons),we classify the stars into five groups.Our analysis reveals that 64%of the spectra show PAH emission,with detections peaking in the stellar effective temperature range 7000–11,000 K(B9–A5).Silicate features appear in 50%of the sample and likewise diminish at higher temperatures.Additionally,we find that future PAH studies can focus on Herbig Ae/Be stars with a spectral index n_(2−24)>−1 and flared morphologies to maximize PAH detections.The 6.2μm PAH band is the most frequently observed in our sample,shifting blueward with increasing stellar temperature,and this is the largest sample yet used to test that peak shift.The weaker 6.0μm feature does not shift with 6.2μm,implying a distinct origin of C=O(carbonyl)or olefinic C=C stretching relative to C–C vibrations.We examined the 11.0/11.2μm PAH ratio using high-resolution Spitzer spectra for the first time in a sample of Herbig Ae/Be stars,finding a range of ionization conditions.This study provides a strong foundation for future JWST observations of intermediate-mass pre-main-sequence stars.展开更多
Classical T Tauri stars (hereinafter CTTS) are protostars formed by collapse of molecular clouds. As they evolve towards the main sequence, CCTS accrete from the circumstellar matter and contract due to self-gravitati...Classical T Tauri stars (hereinafter CTTS) are protostars formed by collapse of molecular clouds. As they evolve towards the main sequence, CCTS accrete from the circumstellar matter and contract due to self-gravitation. Mass accretion and gravitational contraction can accelerate the spin velocities of CTTS up to break-up (～300—400km·s)展开更多
We present the results of a variable star search in a field next to the edge-on galaxies NGC 4565 from the archive data of Beijing-Arizona-Taibei-Connecticut Multicolor Sky Survey. Three new variable stars were discov...We present the results of a variable star search in a field next to the edge-on galaxies NGC 4565 from the archive data of Beijing-Arizona-Taibei-Connecticut Multicolor Sky Survey. Three new variable stars were discovered. Based on spectra obtained from the 2.16m NAOC telescope, we identify two of these as RR Lyr stars and one as a special T Tauri star.展开更多
This paper reports results from the first long-term BV(RI)c photometric CCD observations of three variable pre-main-sequence stars collected during the period from February 2007 to January 2020. The investigated stars...This paper reports results from the first long-term BV(RI)c photometric CCD observations of three variable pre-main-sequence stars collected during the period from February 2007 to January 2020. The investigated stars are located in the field of the PMS star V733 Cep within the Cepheus OB3 association. All stars from our study show rapid photometric variability in all-optical passbands. In this paper, we describe and discuss the photometric behavior of these stars and the possible reasons for their variability. In the light variation of two of the stars, we found periodicity.展开更多
In our previous papers we have improved the value of the orbital period of the binary Herbig Be star HD 200775 and showed that the [O I] and Si II 6347 and 6371 ?A emission lines displayed variations which correlate w...In our previous papers we have improved the value of the orbital period of the binary Herbig Be star HD 200775 and showed that the [O I] and Si II 6347 and 6371 ?A emission lines displayed variations which correlate with the orbital period. In this paper we provide evidences that other broad emission lines of metals in the spectra of HD 200775 also exhibit variability, which is probably related to the orbital cycle of the binary. Analysis was performed based on the high-resolution spectral data collected over a time span of 6 years at the Kourovka Astronomical Observatory of the Ural Federal University(Russia) and the Three College Observatory of the University of North Carolina at Greensboro(USA) as well as archival spectral data compiled since 1994. We report new data points in the radial velocity curve of the He I 5876 ?A line near the extremal values of the radial velocity.展开更多
Results from UBVRI optical photometric observations of the pre-main se- quence star V350 Cep during the period 2004-2014 are presented. The star was dis- covered in 1977 due to its remarkable increase in brightness by...Results from UBVRI optical photometric observations of the pre-main se- quence star V350 Cep during the period 2004-2014 are presented. The star was dis- covered in 1977 due to its remarkable increase in brightness by more than 5 mag （R）. In previous studies, V350 Cep was considered to be a potential FUor or EXor eruptive variable. Our data suggest that during the period of observations the star maintains its maximum brightness with low amplitude photometric variations. Our conclusion is that V350 Cep was probably an intermediate object between FUors and EXors, similar to V1647 Ori.展开更多
This paper reports results from the multicolor photometric observations of 15 pre-main sequence stars collected in the period September 2010-October 2017. The stars from our study are located in the star-forming HII r...This paper reports results from the multicolor photometric observations of 15 pre-main sequence stars collected in the period September 2010-October 2017. The stars from our study are located in the star-forming HII region IC 5070. These objects were previously detected as either emission line stars, flare stars, T Tauri variables or Herbig Ae/Be stars. Photometric observations, especially concerning the long-term behavior of the objects, are missing in the literature. We present the first photometric monitoring for all stars from our study. The analysis of the obtained BV RI photometric data allows us to draw the conclusion that all investigated objects are variable stars. In the case of LkHα 146,we identified previously unknown periodicity in its photometric variability.展开更多
In this paper results from the optical photometric observations of the pre-main sequence star V1180 Cas are reported.The star is a young variable associated with the dark cloud Lynds 1340,located at a distance of 600 ...In this paper results from the optical photometric observations of the pre-main sequence star V1180 Cas are reported.The star is a young variable associated with the dark cloud Lynds 1340,located at a distance of 600 pc from the Sun in the star-forming region in Cassiopeia.V1180 Cas shows large amplitude variability,interpreted as a combination of accretion-induced and extinction-driven effects.Our data from VRI CCD photometric observations of the star were collected from September 2011 to February 2022.During our monitoring,we recorded several brightness dips with large amplitudes of up to 5 mag(I band).At the same time,increases in brightness over periods of several weeks have also been recorded.In this paper,we compare the photometric data obtained for V1180 Cas with observations of other low-mass pre-main sequence objects.展开更多
Long-term BVRI photometric light curves of the pre-main sequence stars V977 Cep and V982 Cep during the period from 2000 October to 2016 August are presented. The stars are located in the vicinity of the reflection ne...Long-term BVRI photometric light curves of the pre-main sequence stars V977 Cep and V982 Cep during the period from 2000 October to 2016 August are presented. The stars are located in the vicinity of the reflection nebula NGC 7129. Our photometric data show that both stars exhibit strong photometric variability in all optical passbands, which is typical for Classical T Tauri stars. Using our observational data we analyze the reasons for the observed brightness variations. In the case of V977 Cep we identify previously unknown periodicity in its light curve.展开更多
We present an analysis of the optical observations of Herbig Ae/Be(HAeBe)star V1686 Cyg,which is associated with a small isolated star-forming region around HAeBe star BD+40?4124.We observed this star as a part of our...We present an analysis of the optical observations of Herbig Ae/Be(HAeBe)star V1686 Cyg,which is associated with a small isolated star-forming region around HAeBe star BD+40?4124.We observed this star as a part of our project investigating young eruptive stars.Observations were conducted on the 2.6-m telescope of Byurakan Observatory from 2015 to 2017.In this period,we obtained direct images of V1686 Cyg and 14 medium-and low-resolution spectra.In the course of observations,we noticed that this star underwent an atypical brightness outburst.After data reduction,we found that the full rise and decline in the brightness of V1686 Cyg had an amplitude of almost 3 magnitudes and lasted about 3 months.We were also able to track changes in the stellar spectrum during the outburst,which are correlated with the photometric variations.展开更多
Results from optical CCD photometric observations of 13 pre-main-sequence stars collected during the period from February 2007 to November 2020 are presented.These stars are located in the association Cepheus OB3,in t...Results from optical CCD photometric observations of 13 pre-main-sequence stars collected during the period from February 2007 to November 2020 are presented.These stars are located in the association Cepheus OB3,in the field of the young star V733 Cephei.Photometric observations,especially concerning the long-term variability of the stars,are missing in the literature.We present the first longterm V(RI)c monitoring for them,that cover 13 years.Results from our study indicate that all of the investigated stars manifest strong photometric variability.The presented paper is a part of our program for the photometric study of pre-main-sequence stars located in active star-forming regions.展开更多
基金the Italian CNAA and MURST (COFIN) grantsthe DST-RFBR project INT/RUS/RFBR/P271BRICS grant number DST/IMRCD/BRICS/PilotCall1/ProFCheap/2017(G) for part of the present work
文摘Using long-term optical, ultraviolet(UV) and X-ray data, we present a study of a classical T Tauri star CV Cha. The V-band light curve obtained from the All Sky Automated Survey(ASAS) shows short as well as long-term variability. The short-term variability could be due to rotational modulation of CV Cha. We derive the rotational period of 3.714 ± 0.001 d for CV Cha. UV light curves obtained from Swift also show the variations. X-ray light curves from XMM-Newton and Swift do not show any significant short as well as long-term variability. However, the light curve from Chandra appears to be variable, which could be due to the emergence of flaring activities. X-ray spectra from all observations are explained well by the single temperature plasma of 0.95 keV with X-ray luminosity of 1030.4erg s-1in the 0.5–7.5 keV energy band. It appears that variability in optical and UV bands could be due to the presence of both hot and cool spots on the surface, while X-ray emission is dominated by magnetic processes.
基金supported by a Grant-in-Aid for Scientific Research (No. 24540231)supported by the U.S. National Science Foundation under Award (No. 1009203)
文摘A high angular resolution near-infrared image that shows the intensity of polarization for the GG Tau A binary system was obtained with the Subaru Telescope. The image shows a circumbinary disk scattering the light from the central binary. The azimuthal profile of the intensity of polarization for the circumbinary disk is roughly reproduced by a simple disk model with the Henyey-Greenstein phase function and the Rayleigh function, indicating there are small dust grains at the surface of the disk. Combined with a previous observation of the circumbinary disk, our image indicates that the gap structure in the circumbinary disk orbits counterclockwise, but material in the disk orbits clockwise. We propose that there is a shadow caused by material located between the central binary and the circumbinary disk. The separations and position angles of the stellar components of the binary in the past 20 yr are consistent with the binary orbit with a = 33.4 AU and e = 0.34.
文摘We report the results of optical spectroscopic monitoring observations of a T Tauri star, V409 Tau. A previous photometric study indicated that this star experienced dimming events due to the obscuration of light from the central star with a distorted circumstellar disk. We conducted medium-resolution (R ~10,000) spectroscopic observations with 2-m Nayuta telescope at Nishi-Harima Astronomical Observatory. Spectra were obtained in 18 nights between November 2015 and March 2016. Several absorption lines such as Ca I and Li, and the Hαemission line were confirmed in the spectra. The Ic-band magnitudes of V409 Tau changed by approximately 1 magnitude during the observation epoch. The equivalent widths of the five absorption lines are roughly constant despite changes in the Ic-band magnitudes. We conclude that the light variation of the star is caused by the obscuration of light from the central star with a distorted circumstellar disk, based on the relationship between the equivalent widths of the absorption lines and the Ic-band magnitudes. The blue component of the Hαemission line was dominant during the observation epoch, and an inverse P Cygni profile was observed in eight of the spectra. The time-variable inverse P Cygni profile of the Hαemission line indicates unsteady mass accretion from the circumstellar disk to the central star.
基金financial support from CHRIST(Deemed to be University,Bangalore)through the SEED money projects(No:SMSS-2335,11/2023&SMSS-2220,12/2022)by the SERB project(CRG/2023/005271).
文摘We present a comprehensive mid-infrared spectroscopic survey of 124 Herbig Ae/Be stars using newly processed Spitzer/IRS spectra from the newly released CASSISjuice database.Based on prominent dust and molecular signatures(polycyclic aromatic hydrocarbons(PAHs),silicates,and hydrogenated amorphous carbons),we classify the stars into five groups.Our analysis reveals that 64%of the spectra show PAH emission,with detections peaking in the stellar effective temperature range 7000–11,000 K(B9–A5).Silicate features appear in 50%of the sample and likewise diminish at higher temperatures.Additionally,we find that future PAH studies can focus on Herbig Ae/Be stars with a spectral index n_(2−24)>−1 and flared morphologies to maximize PAH detections.The 6.2μm PAH band is the most frequently observed in our sample,shifting blueward with increasing stellar temperature,and this is the largest sample yet used to test that peak shift.The weaker 6.0μm feature does not shift with 6.2μm,implying a distinct origin of C=O(carbonyl)or olefinic C=C stretching relative to C–C vibrations.We examined the 11.0/11.2μm PAH ratio using high-resolution Spitzer spectra for the first time in a sample of Herbig Ae/Be stars,finding a range of ionization conditions.This study provides a strong foundation for future JWST observations of intermediate-mass pre-main-sequence stars.
基金Project supported by the National Natural Science Foundation of China.
文摘Classical T Tauri stars (hereinafter CTTS) are protostars formed by collapse of molecular clouds. As they evolve towards the main sequence, CCTS accrete from the circumstellar matter and contract due to self-gravitation. Mass accretion and gravitational contraction can accelerate the spin velocities of CTTS up to break-up (～300—400km·s)
基金Supported by the National Natural Science Foundation of China.
文摘We present the results of a variable star search in a field next to the edge-on galaxies NGC 4565 from the archive data of Beijing-Arizona-Taibei-Connecticut Multicolor Sky Survey. Three new variable stars were discovered. Based on spectra obtained from the 2.16m NAOC telescope, we identify two of these as RR Lyr stars and one as a special T Tauri star.
基金partly supported by the Bulgarian Ministry of Education and Science under the National Program for Research“Young Scientists and Postdoctoral Students”partial support by grant DN 18-13/2017 from the Bulgarian National Science Fund。
文摘This paper reports results from the first long-term BV(RI)c photometric CCD observations of three variable pre-main-sequence stars collected during the period from February 2007 to January 2020. The investigated stars are located in the field of the PMS star V733 Cep within the Cepheus OB3 association. All stars from our study show rapid photometric variability in all-optical passbands. In this paper, we describe and discuss the photometric behavior of these stars and the possible reasons for their variability. In the light variation of two of the stars, we found periodicity.
基金supported by the Ministry of Education and Science (the basic part of theState assignment, RK No. AAAA-A17-117030310283-7)and by Act No. 211 of the Government of the Russian Federation, agreement 02.A03.21.0006
文摘In our previous papers we have improved the value of the orbital period of the binary Herbig Be star HD 200775 and showed that the [O I] and Si II 6347 and 6371 ?A emission lines displayed variations which correlate with the orbital period. In this paper we provide evidences that other broad emission lines of metals in the spectra of HD 200775 also exhibit variability, which is probably related to the orbital cycle of the binary. Analysis was performed based on the high-resolution spectral data collected over a time span of 6 years at the Kourovka Astronomical Observatory of the Ural Federal University(Russia) and the Three College Observatory of the University of North Carolina at Greensboro(USA) as well as archival spectral data compiled since 1994. We report new data points in the radial velocity curve of the He I 5876 ?A line near the extremal values of the radial velocity.
基金supported by ESF and the Bulgarian Ministry of Education and Science under the contract BG051PO001-3.3.06-0047
文摘Results from UBVRI optical photometric observations of the pre-main se- quence star V350 Cep during the period 2004-2014 are presented. The star was dis- covered in 1977 due to its remarkable increase in brightness by more than 5 mag （R）. In previous studies, V350 Cep was considered to be a potential FUor or EXor eruptive variable. Our data suggest that during the period of observations the star maintains its maximum brightness with low amplitude photometric variations. Our conclusion is that V350 Cep was probably an intermediate object between FUors and EXors, similar to V1647 Ori.
基金funded by the National Aeronautics and Space Administrationthe National Science Foundation+1 种基金partly supported by the National Science Fund of the Ministry of Education and Science of Bulgaria under grants DM 08-2/2016, DN 08-1/2016, DN 08-20/2016 and DN 18-13/2017funds of the project RD-08112/2018 of the University of Shumen
文摘This paper reports results from the multicolor photometric observations of 15 pre-main sequence stars collected in the period September 2010-October 2017. The stars from our study are located in the star-forming HII region IC 5070. These objects were previously detected as either emission line stars, flare stars, T Tauri variables or Herbig Ae/Be stars. Photometric observations, especially concerning the long-term behavior of the objects, are missing in the literature. We present the first photometric monitoring for all stars from our study. The analysis of the obtained BV RI photometric data allows us to draw the conclusion that all investigated objects are variable stars. In the case of LkHα 146,we identified previously unknown periodicity in its photometric variability.
基金partly supported by the National RI Roadmap Project(contracts D01-383/18.12.2020 and D01-176/29.07.2022)of the Ministry of Education and Science of the Republic of Bulgaria。
文摘In this paper results from the optical photometric observations of the pre-main sequence star V1180 Cas are reported.The star is a young variable associated with the dark cloud Lynds 1340,located at a distance of 600 pc from the Sun in the star-forming region in Cassiopeia.V1180 Cas shows large amplitude variability,interpreted as a combination of accretion-induced and extinction-driven effects.Our data from VRI CCD photometric observations of the star were collected from September 2011 to February 2022.During our monitoring,we recorded several brightness dips with large amplitudes of up to 5 mag(I band).At the same time,increases in brightness over periods of several weeks have also been recorded.In this paper,we compare the photometric data obtained for V1180 Cas with observations of other low-mass pre-main sequence objects.
基金supported partly by funds of the project‘Multicolor photometric study of Pre-main sequence stars from selected star-forming regions’financed by Fund for Scientific Research of the Bulgarian Ministry of Education and Scienceuse of NASA’s Astrophysics Data System Abstract Service+2 种基金the SIMBAD database and the Vizie R catalogue access tool,operated at CDS,Strasbourg,Francefunded by the National Aeronautics and Space Administration and the National Science Foundation(Skrutskie et al.2006)supported partly by funds from the project RD-08-81 at the University of Shumen
文摘Long-term BVRI photometric light curves of the pre-main sequence stars V977 Cep and V982 Cep during the period from 2000 October to 2016 August are presented. The stars are located in the vicinity of the reflection nebula NGC 7129. Our photometric data show that both stars exhibit strong photometric variability in all optical passbands, which is typical for Classical T Tauri stars. Using our observational data we analyze the reasons for the observed brightness variations. In the case of V977 Cep we identify previously unknown periodicity in its light curve.
基金supported by the RA MES State Committee of Science,in the frame of the research project number 18T-1C-329。
文摘We present an analysis of the optical observations of Herbig Ae/Be(HAeBe)star V1686 Cyg,which is associated with a small isolated star-forming region around HAeBe star BD+40?4124.We observed this star as a part of our project investigating young eruptive stars.Observations were conducted on the 2.6-m telescope of Byurakan Observatory from 2015 to 2017.In this period,we obtained direct images of V1686 Cyg and 14 medium-and low-resolution spectra.In the course of observations,we noticed that this star underwent an atypical brightness outburst.After data reduction,we found that the full rise and decline in the brightness of V1686 Cyg had an amplitude of almost 3 magnitudes and lasted about 3 months.We were also able to track changes in the stellar spectrum during the outburst,which are correlated with the photometric variations.
基金partly supported by the National Science Fund of the Ministry of Education and Science of Bulgaria under grant DN 18-10/2017funds of the project RD-08-125/2021 of the University of Shumen。
文摘Results from optical CCD photometric observations of 13 pre-main-sequence stars collected during the period from February 2007 to November 2020 are presented.These stars are located in the association Cepheus OB3,in the field of the young star V733 Cephei.Photometric observations,especially concerning the long-term variability of the stars,are missing in the literature.We present the first longterm V(RI)c monitoring for them,that cover 13 years.Results from our study indicate that all of the investigated stars manifest strong photometric variability.The presented paper is a part of our program for the photometric study of pre-main-sequence stars located in active star-forming regions.
