This study assesses the implementation of energy conservation opportunities in four-star and five-star hotels in Nairobi. The Covid-19 pandemic had a significant impact on the Hospitality Industry. Currently, there is...This study assesses the implementation of energy conservation opportunities in four-star and five-star hotels in Nairobi. The Covid-19 pandemic had a significant impact on the Hospitality Industry. Currently, there is a growing inclination to furnish vips with superior and sustainable services in an energy-efficient and eco-friendly way. Comprehensive research was conducted from energy audits gathered from the establishments and contracted auditing companies, on top of this, hotel staff were given digital questionnaires. To add to the data, the researcher surveyed the hotels with engineering managers. The Energy Audits found that all 10 hotels had adopted Energy Conservation Opportunities (ECOs). After further analysis, the mean adoption rate of Energy Conservation Opportunities (ECOs) during the past three years was 55.83%, which was below the aim of 100%. According to studies, hotel staff manages energy to cut costs. The researcher found that hotels use up a lot of energy. However, they have conservation potential, depending on government policies, costs, ease of implementation, and management commitment to sustainable practices. Essentially, Energy Conservation Opportunities (ECOs) reduce energy expenditures and boost reliable revenues, especially during high energy prices and uncertainty.展开更多
SN 2014av is a type Ibn supernova(SN)characterized by the interaction between the SN ejecta and a helium-rich circumstellar medium(CSM).We use the^(56)Ni model,the ejecta-CSM interaction(CSI)model,and the CSI plus^(56...SN 2014av is a type Ibn supernova(SN)characterized by the interaction between the SN ejecta and a helium-rich circumstellar medium(CSM).We use the^(56)Ni model,the ejecta-CSM interaction(CSI)model,and the CSI plus^(56)Ni model to fit the multiband light curves(LCs)of SN 2014av.For the CSI and CSI plus^(56)Ni models,we assume that the CSM is a constant density shell(“shell”)or a steady-state stellar wind(“wind”)with density∝r-2.We find that both the^(56)Ni and CSI models fail to fit the multiband LCs of SN 2014av,while the CSI plus^(56)Ni model can account for the LCs.In the last scenario,the LCs around the peaks were mainly powered by the CSI,while the flattening of the LCs was mainly powered by the radioactive decay of^(56)Ni.For the wind case,the derived mass-loss rate of the progenitor is≈20.5-205.5 M_(⊙)yr^(-1),whose lower limit is significantly larger than the upper limit of normal stellar winds,and comparable the upper limit of hyper-winds.Hence,we suggest that the wind case is disfavored.For the shell case,the best-fitting values of the ejecta,^(56)Ni,and the CSM are2.29 M_(⊙),0.09 M_(⊙),and 5.00 M_(⊙),respectively.Provided the velocity of the CSM shell is 100-1000 km s^(-1),we infer that the shell might be expelled≈0.49-5.20 yr before the SN exploded.展开更多
The central compact object XMMU J173203.3-344518 in the supernova remnant HESS J1731-347 challenges conventional neutron star models due to its low mass M=0.77_(-0.17)^(+0.20)M■and high redshifted surface temperature...The central compact object XMMU J173203.3-344518 in the supernova remnant HESS J1731-347 challenges conventional neutron star models due to its low mass M=0.77_(-0.17)^(+0.20)M■and high redshifted surface temperature T_(s)^(∞)=156_(-6)^(+6)e V (1.81_(-0.07)^(+0.07)×10^(6)K).We investigate the observational properties of XMMU J173203.3-344518 within a color-flavor-locked(CFL) phase strange star model.We construct a thermal evolution model of the CFL phase strange star,along with heating due to the viscous dissipation of r-mode oscillations.Employing one of th most widely used quark matter equations of state,we characterize the star properties by the strange quark mas(ms),effective bag constant (Beff),perturbative QCD correction (a4),and pairing gap (Δ).Our analysi demonstrates that the observed properties of XMMU J173203.3344518 can be explained by r-mode heating with CFL strange star,provided that the initial spin period is shorter than 18 ms.We constrain the r-mode saturation amplitude to 8×10^(-3)–1.4×10^(-2)and predict a current spin period of 6–9 ms for an initial period of 1 ms.Thi rapid rotation is consistent with the absence of detected pulsations.The r-mode instability window remains robus across a wide range of pairing gap values (5–200 MeV),providing a reliable framework for interpretation regardless of microscopic uncertainties.Our results support the identification of XMMU J173203.3344518 as rapidly rotating,low-mass CFL phase strange star,demonstrating the importance of r-mode heating in the therma evolution of compact objects with exotic dense matter.展开更多
In this paper,we determine the photosphere evolution of PTF11rka which is a type Ic supernova (SN) by fitting its spectral energy distributions at different epochs.We find that the photosphere of PTF11rka expanded at ...In this paper,we determine the photosphere evolution of PTF11rka which is a type Ic supernova (SN) by fitting its spectral energy distributions at different epochs.We find that the photosphere of PTF11rka expanded at a constant velocity at early epochs,and the photosphere temperature increased slightly after reaching a minimum.These features are reminiscent of those of SN 2017dio.Based on the photosphere module that can describe the photosphere evolution of PTF11rka,we use the ^(56)Ni cascade decay model to fit its multiband light curves (LCs),finding that the model can well fit the photometric data.The derived ejecta mass and ^(56)Ni mass are respectively 8.76■ and 0.29-0.41■;the derived peak luminosity and the rise time of the theoretical bolometric LC of PTF11rka are ~8.24×10^(42)erg s^(-1) and ~35 days,respectively.Moreover,we find that the theoretical multiband LCs and the theoretical bolometric LC of PTF11rka do not show early-time excesses proposed in the literature.This indicates that additional energy sources (e.g.,the interaction between the ejecta and the circumstellar material)suggested to be responsible for the early-time excess can be neglected.展开更多
Type Ia supernovae(SNe Ia)are among the most extreme phenomena in the Universe and play a crucial role in the studies of stellar evolution,galactic chemical evolution and cosmology.However,the progenitors of SNe Ia ar...Type Ia supernovae(SNe Ia)are among the most extreme phenomena in the Universe and play a crucial role in the studies of stellar evolution,galactic chemical evolution and cosmology.However,the progenitors of SNe Ia are still under debate.It has been suggested that SNe Ia could be produced by helium(He)novae in the singledegenerate channel.Recently,a He nova named[HP99]159 was proposed to be a progenitor candidate for SNe Ia,in which the white dwarf(WD)has a mass of 1.2_(0.4)^(+0.18)M_(⊙),the He star’s mass ranges from 0.8M_(⊙)to 2.0M_(⊙)and the orbital period was suggested to be 2.33 or 1.16 days.In the present work,we evolved a large number of primordial binaries to the formation of WD+He star systems and investigated their future evolution.We provided a representative evolutionary track of[HP99]159 and found that[HP99]159 may originate from a primordial binary with a 6.16M_(⊙)primary and a 4.32M_(⊙)secondary with an initial orbital period of 5110 days.We also found that[HP99]159 might evolve to an SN Ia explosion as suggested by previous studies,or it may also form an accretion-induced collapse event or a wide double WD.Further detailed observations are needed in future studies to provide more information about the precise nature of[HP99]159.展开更多
We present multi-color photometric observations and a one-dimensional spectrum, acquired from March 2016 to May 2017, for the short-period eclipsing binary PS Vir, by using the 2.16-m, 85-cm and 60-cm telescopes at Xi...We present multi-color photometric observations and a one-dimensional spectrum, acquired from March 2016 to May 2017, for the short-period eclipsing binary PS Vir, by using the 2.16-m, 85-cm and 60-cm telescopes at Xinglong station, which is administered by National Astronomical Observatories, Chinese Academy of Sciences. The spectral type was determined as G2V from the one-dimensional spectrum. The photometric solution was reduced from BVRc light curves. The results imply that PS Vir is a W-subtype contact binary with a mass ratio of q - 0.305（zk0.008） and a fill-out factor of f = 14.4（＋1.8）%. The orbital period may be undergoing a cyclic oscillation with an ampli-tude of A = 0.0027（~0.0001）d and a modulated period of 11.7（4-0.2） yr, which may result from the light-time effect due to a third body. The lower limit on mass for the assumed component is 0.12 Me. Moreover, the more massive component of PS Vir may be a bit more evolved star as determined from the mass-luminosity diagram.展开更多
Based on long-term high-resolution spectroscopic observations obtained during five observing runs from 2001 to 2004, we study optical flare events and chromospheric activity variability of the very active RS CVn star ...Based on long-term high-resolution spectroscopic observations obtained during five observing runs from 2001 to 2004, we study optical flare events and chromospheric activity variability of the very active RS CVn star UX Ari. By means of the spectral subtraction technique, several optical chromospheric activity indicators （including the He IDa, Na I D1, D2 doublet, Ha and Ca II IRT lines） covered in our echelle spectra were analyzed. Four large optical flare events were detected on UX Ari during our observations, which show prominent He I D3 line emission together with great enhancement in emission of the Ha and Ca II IRT lines and strong filled-in or emission reversal features in the Na ! D1, D2 doublet lines. The newly detected flares are much more energetic than previous discoveries, especially for the flare identified during the 2002 December observing run. Optical flare events on UX Ari are more likely to be observed around two quadratures of the system, except for our optical flares detected during the 2004 November observing run. Moreover, we have found rotational modulation of chromospheric activity in the Ha and Ca II IRT lines, which suggests the presence of chromospherically active longitudes over the surface of UX Ari. The change in chromospherically active longitudes among our observing runs, as well as the variation in chromospheric activity level from 2001 to 2004, indicates a long-term evolution of active regions.展开更多
We present the first results of a time-resolved CCD photometric and time-series analysis of NSV 13601,a variable star in the constellation Pegasus.The 14′′Schmidt-Cassegrain telescope of Maharaja Krishnakumarsinhji ...We present the first results of a time-resolved CCD photometric and time-series analysis of NSV 13601,a variable star in the constellation Pegasus.The 14′′Schmidt-Cassegrain telescope of Maharaja Krishnakumarsinhji Bhavnagar University(MKBU)was used for observations.Analysis was performed both in VStar and Period04 software,and their results were compared.The main results are as follows:From data analysis,its has period^77.784 d(MKBU data V)(VStar),~77.632 d(MKBU data Ic)(VStar),~77.058 d(MKBU data V)(Period04)and^49.560 d(MKBU data Ic)(Period04).Its V and I mean magnitudes for MKBU data are 12.203(V)and 11.292(I)mag respectively.We confirm it to be a variable star.展开更多
A massive star is defined as one with mass greater than - 8-10.M⊙. Central to the on-going debate on how these objects [massive stars] come into being is the so-called Radiation Problem. For nearly forty years, it ha...A massive star is defined as one with mass greater than - 8-10.M⊙. Central to the on-going debate on how these objects [massive stars] come into being is the so-called Radiation Problem. For nearly forty years, it has been argued that the radiation field emanating from massive stars is high enough to cause a global re- versal of direct radial in-fall of material onto the nascent star. We argue that only in the case of a non-spinning isolated star does the gravitational field of the nascent star overcome the radiation field. An isolated non-spinning star is a non-spinning star without any circumstellar material around it, and the gravitational field beyond its surface is described exactly by Newton＇s inverse square law. The supposed fact that massive stars have a gravitational field that is much stronger than their radiation field is drawn from the analysis of an isolated massive star. In this case the gravitational field is much stronger than the radiation field. This conclusion has been erroneously extended to the case of massive stars enshrouded in gas and dust. We find that, for the case of a non- spinning gravitating body where we take into consideration the circumstellar material, at ,- 8-10M⊙, the radiation field will not reverse the radial in-fall of matter, but rather a stalemate between the radiation and gravitational field will be achieved, i.e. the infall is halted but not reversed. This picture is very different from the common picture that is projected and accepted in the popular literature where at -8-10 M⊙, all the circumstellar material, from the surface of the star right up to the edge of the molec- ular core, is expected to be swept away by the radiation field. We argue that massive stars should be able to start their normal stellar processes if the molecular core from which they form has some rotation, because a rotating core exhibits an Azimuthally Symmetric Gravitational Field which causes there to be an accretion disk and along this equatorial disk. The radiation field cannot be much stronger than the gravitational field, hence this equatorial accretion disk becomes the channel via which the nascent massive star accretes all of its material.展开更多
We analyze the frequencies of three known roAp stars,TIC 96315731,TIC 72392575,and TIC 318007796,using the light curves from the Transiting Exoplanet Survey Satellite.For TIC 96315731,the rotational and pulsational fr...We analyze the frequencies of three known roAp stars,TIC 96315731,TIC 72392575,and TIC 318007796,using the light curves from the Transiting Exoplanet Survey Satellite.For TIC 96315731,the rotational and pulsational frequencies are 0.1498360 day^(-1)and 165.2609 day^(-1),respectively.In the case of TIC 72392575,the rotational frequency is 0.25551 day^(-1).We detect a quintuplet of pulsation frequencies with a center frequency of135.9233 day^(-1),along with two signals within the second pair of rotational sidelobes of the quintuplet separated by the rotation frequency.These two signals may correspond to the frequencies of a dipole mode.In TIC318007796,the rotational and pulsational frequencies are 0.2475021 day^(-1),192.73995 day^(-1),and196.33065 day^(-1),respectively.Based on the oblique pulsator model,we calculate the rotation inclination(i)and magnetic obliquity angle(b)for the stars,which provide the geometry of the pulsation modes.Combining the phases of the frequency quintuplets,the pulsation amplitude and phase modulation curves,and the results of spherical harmonic decomposition,we conclude that the pulsation modes of frequency quintuplets in TIC96315731,TIC 72392575,and TIC 318007796 correspond to distorted dipole mode,distorted quadrupole mode,and distorted dipole mode,respectively.展开更多
KIC 10417986 is a short orbital period(0.0737 day)ellipsoidal variable star with aδSct andγDor hybrid pulsation component discovered by Kepler.The ground-based spectroscopic observations were carried out in the wint...KIC 10417986 is a short orbital period(0.0737 day)ellipsoidal variable star with aδSct andγDor hybrid pulsation component discovered by Kepler.The ground-based spectroscopic observations were carried out in the winters of 2020 and 2021 to investigate the binary nature of this star.We derive the orbital parameters using the rvfit code with a result of K_(1)=29.7±1.5 km s^(-1),γ=-18.7±1.7 km s^(-1),and confirm an orbital period of 0.84495 day instead of the result given by Kepler.The atmospheric parameters of the primary are determined by the synthetic spectral fitting technique with the estimated values of T_(eff)=7411±187 K,log g=4.2±0.3 dex,[M/H]=0.08±0.09 dex and vsini=52±11 km s^(-1).KIC 10417986 is a circular orbit binary system.From the single-lined nature and mass function of the star,the derived orbital inclination is 26°±6°,and the mass of the secondary is 0.52_(-0.09)^(+0.18)M_(⊙),which should be a late-K to early-M type star.Fourteen frequencies are extracted from Kepler light curves,of which six independent frequencies in the high-frequency region are identified as the p-mode pulsations ofδSct star,and one independent frequency in the low-frequency region(f_(2)=1.3033 cd^(-1))is probably the rotational frequency due to the starspots rather than the ellipsoidal effect.展开更多
The aim of this paper is to determinate the fundamental parameters of six exoplanet host （EH） stars and their planets. Because techniques for detecting exo- planets yield properties of the planet only as a function ...The aim of this paper is to determinate the fundamental parameters of six exoplanet host （EH） stars and their planets. Because techniques for detecting exo- planets yield properties of the planet only as a function of the properties of the host star, we must accurately determine the parameters of the EH stars first. For this rea- son, we constructed a grid of stellar models including diffusion and rotation-induced extra-mixing with given ranges of input parameters （i.e. mass, metallicity and initial rotation rate）. In addition to the commonly used observational constraints such as the effective temperature Tell, luminosity L and metallicity [Fe/H], we added two obser- vational constraints, the lithium abundance log N （Li） and the rotational period Prot. These two additional observed parameters can set further constraints on the model due to their correlations with mass, age and other stellar properties. Hence, our estimations of the fundamental parameters for these EH stars and their planets have a higher preci- sion than previous works. Therefore, the combination of rotational period and lithium helps us to obtain more accurate parameters for stars, leading to an improvement in knowledge about the physical state of EH stars and their planets.展开更多
IO Cnc was classified to be a new G-type(G0)W UMa-type eclipsing binary system.Our first multicolor photometric solutions show that IO Cnc is a new W-subtype shallow contact binary with a fill-out factor of f=16.1%and...IO Cnc was classified to be a new G-type(G0)W UMa-type eclipsing binary system.Our first multicolor photometric solutions show that IO Cnc is a new W-subtype shallow contact binary with a fill-out factor of f=16.1%and a low mass ratio of q=3.12(or 1/q=0.32).During orbital period investigations,a cyclic variation and a downward parabolic variation with a rate of(-1.28±0.43)×10^(-7) d yr^(-1) was discovered in the observed–calculated(O-C)curve.The cyclic variation was analyzed by the light travel time effect(LTTE)via a potential red dwarf companion star,an orbital semi-major axis shorter than 4.88±0.82 AU was obtained.Finally,we collect physical parameters of a sample of 50 G-type shallow contact binaries(f≤20%),it is suggested that most of the G-type shallow contact binaries are undergoing a longterm and periodic orbital period changes,especially more systems show long-term decreases.The long-term orbital period decrease indicates that IO Cnc is in a mass transferring from the more massive component to the less massive one.With the long-term decrease of the orbital period,this shallow contact binary will evolve into a deeper contact one.展开更多
文摘This study assesses the implementation of energy conservation opportunities in four-star and five-star hotels in Nairobi. The Covid-19 pandemic had a significant impact on the Hospitality Industry. Currently, there is a growing inclination to furnish vips with superior and sustainable services in an energy-efficient and eco-friendly way. Comprehensive research was conducted from energy audits gathered from the establishments and contracted auditing companies, on top of this, hotel staff were given digital questionnaires. To add to the data, the researcher surveyed the hotels with engineering managers. The Energy Audits found that all 10 hotels had adopted Energy Conservation Opportunities (ECOs). After further analysis, the mean adoption rate of Energy Conservation Opportunities (ECOs) during the past three years was 55.83%, which was below the aim of 100%. According to studies, hotel staff manages energy to cut costs. The researcher found that hotels use up a lot of energy. However, they have conservation potential, depending on government policies, costs, ease of implementation, and management commitment to sustainable practices. Essentially, Energy Conservation Opportunities (ECOs) reduce energy expenditures and boost reliable revenues, especially during high energy prices and uncertainty.
基金supported by the National Key R&D Program(2024YFA1611700)the National Natural Science Foundation of China(grant Nos.12133003,12494571 and 11963001)supported by the Guangxi Talent Program(“Highland of Innovation Talents”)and Program of Bagui Scholars(LHJ)。
文摘SN 2014av is a type Ibn supernova(SN)characterized by the interaction between the SN ejecta and a helium-rich circumstellar medium(CSM).We use the^(56)Ni model,the ejecta-CSM interaction(CSI)model,and the CSI plus^(56)Ni model to fit the multiband light curves(LCs)of SN 2014av.For the CSI and CSI plus^(56)Ni models,we assume that the CSM is a constant density shell(“shell”)or a steady-state stellar wind(“wind”)with density∝r-2.We find that both the^(56)Ni and CSI models fail to fit the multiband LCs of SN 2014av,while the CSI plus^(56)Ni model can account for the LCs.In the last scenario,the LCs around the peaks were mainly powered by the CSI,while the flattening of the LCs was mainly powered by the radioactive decay of^(56)Ni.For the wind case,the derived mass-loss rate of the progenitor is≈20.5-205.5 M_(⊙)yr^(-1),whose lower limit is significantly larger than the upper limit of normal stellar winds,and comparable the upper limit of hyper-winds.Hence,we suggest that the wind case is disfavored.For the shell case,the best-fitting values of the ejecta,^(56)Ni,and the CSM are2.29 M_(⊙),0.09 M_(⊙),and 5.00 M_(⊙),respectively.Provided the velocity of the CSM shell is 100-1000 km s^(-1),we infer that the shell might be expelled≈0.49-5.20 yr before the SN exploded.
基金supported in part by the Natural Science Foundation of Xinjiang Uygur Autonomous Region (No.2023D01E20)the National Key R&D Program of China (No.2022YFA1603104)+3 种基金the National Natural Science Foundation of China (Nos.12288102,12273028 and 12033001)the Tianshan talents program (2023TSYCTD0013)the Major Science and Technology Program of Xinjiang Uygur Autonomous Region (No.2022A03013-1)the Urumqi Nanshan Astronomy and Deep Space Exploration Observation and Research Station of Xinjiang (XJYWZ2303)。
文摘The central compact object XMMU J173203.3-344518 in the supernova remnant HESS J1731-347 challenges conventional neutron star models due to its low mass M=0.77_(-0.17)^(+0.20)M■and high redshifted surface temperature T_(s)^(∞)=156_(-6)^(+6)e V (1.81_(-0.07)^(+0.07)×10^(6)K).We investigate the observational properties of XMMU J173203.3-344518 within a color-flavor-locked(CFL) phase strange star model.We construct a thermal evolution model of the CFL phase strange star,along with heating due to the viscous dissipation of r-mode oscillations.Employing one of th most widely used quark matter equations of state,we characterize the star properties by the strange quark mas(ms),effective bag constant (Beff),perturbative QCD correction (a4),and pairing gap (Δ).Our analysi demonstrates that the observed properties of XMMU J173203.3344518 can be explained by r-mode heating with CFL strange star,provided that the initial spin period is shorter than 18 ms.We constrain the r-mode saturation amplitude to 8×10^(-3)–1.4×10^(-2)and predict a current spin period of 6–9 ms for an initial period of 1 ms.Thi rapid rotation is consistent with the absence of detected pulsations.The r-mode instability window remains robus across a wide range of pairing gap values (5–200 MeV),providing a reliable framework for interpretation regardless of microscopic uncertainties.Our results support the identification of XMMU J173203.3344518 as rapidly rotating,low-mass CFL phase strange star,demonstrating the importance of r-mode heating in the therma evolution of compact objects with exotic dense matter.
基金supported by the National Natural Science Foundation of China (NSFC,grant Nos.12494571,11963001 and 12133003)supported by the Program of Bagui Scholars (LHJ)。
文摘In this paper,we determine the photosphere evolution of PTF11rka which is a type Ic supernova (SN) by fitting its spectral energy distributions at different epochs.We find that the photosphere of PTF11rka expanded at a constant velocity at early epochs,and the photosphere temperature increased slightly after reaching a minimum.These features are reminiscent of those of SN 2017dio.Based on the photosphere module that can describe the photosphere evolution of PTF11rka,we use the ^(56)Ni cascade decay model to fit its multiband light curves (LCs),finding that the model can well fit the photometric data.The derived ejecta mass and ^(56)Ni mass are respectively 8.76■ and 0.29-0.41■;the derived peak luminosity and the rise time of the theoretical bolometric LC of PTF11rka are ~8.24×10^(42)erg s^(-1) and ~35 days,respectively.Moreover,we find that the theoretical multiband LCs and the theoretical bolometric LC of PTF11rka do not show early-time excesses proposed in the literature.This indicates that additional energy sources (e.g.,the interaction between the ejecta and the circumstellar material)suggested to be responsible for the early-time excess can be neglected.
基金supported by the National Natural Science Foundation of China(NSFC,grant Nos.12288102,12225304,and 12090040/12090043)the National Key R&D Program of China(No.2021YFA1600404)+3 种基金the Western Light Project of CAS(No.XBZG-ZDSYS-202117)the Yunnan Revitalization Talent Support Program(Yunling Scholar Project)the Yunnan Fundamental Research Project(No.202201BC070003)the International Centre of Supernovae,Yunnan Key Laboratory(No.202302AN360001).
文摘Type Ia supernovae(SNe Ia)are among the most extreme phenomena in the Universe and play a crucial role in the studies of stellar evolution,galactic chemical evolution and cosmology.However,the progenitors of SNe Ia are still under debate.It has been suggested that SNe Ia could be produced by helium(He)novae in the singledegenerate channel.Recently,a He nova named[HP99]159 was proposed to be a progenitor candidate for SNe Ia,in which the white dwarf(WD)has a mass of 1.2_(0.4)^(+0.18)M_(⊙),the He star’s mass ranges from 0.8M_(⊙)to 2.0M_(⊙)and the orbital period was suggested to be 2.33 or 1.16 days.In the present work,we evolved a large number of primordial binaries to the formation of WD+He star systems and investigated their future evolution.We provided a representative evolutionary track of[HP99]159 and found that[HP99]159 may originate from a primordial binary with a 6.16M_(⊙)primary and a 4.32M_(⊙)secondary with an initial orbital period of 5110 days.We also found that[HP99]159 might evolve to an SN Ia explosion as suggested by previous studies,or it may also form an accretion-induced collapse event or a wide double WD.Further detailed observations are needed in future studies to provide more information about the precise nature of[HP99]159.
基金funding from the National Natural Science Foundation of China(Nos.11473009 and U1231102)the Outstanding Young Talents Program of the Education Department of Anhui Province (No.gxyq2018161)supported by the Open Project Program of the Key Laboratory of Optical Astronomy,National Astronomical Observatories,Chinese Academy of Sciences
文摘We present multi-color photometric observations and a one-dimensional spectrum, acquired from March 2016 to May 2017, for the short-period eclipsing binary PS Vir, by using the 2.16-m, 85-cm and 60-cm telescopes at Xinglong station, which is administered by National Astronomical Observatories, Chinese Academy of Sciences. The spectral type was determined as G2V from the one-dimensional spectrum. The photometric solution was reduced from BVRc light curves. The results imply that PS Vir is a W-subtype contact binary with a mass ratio of q - 0.305（zk0.008） and a fill-out factor of f = 14.4（＋1.8）%. The orbital period may be undergoing a cyclic oscillation with an ampli-tude of A = 0.0027（~0.0001）d and a modulated period of 11.7（4-0.2） yr, which may result from the light-time effect due to a third body. The lower limit on mass for the assumed component is 0.12 Me. Moreover, the more massive component of PS Vir may be a bit more evolved star as determined from the mass-luminosity diagram.
基金partially supported by the Open Project Program of the Key Laboratory of Optical Astronomy,National Astronomical Observatories,Chinese Academy of SciencesThe present study is also supported by the National Natural Science Foundation of China(Grant Nos.10373023,10773027 and 11333006)Chinese Academy of Sciences project(No.KJCX2-YW-T24)
文摘Based on long-term high-resolution spectroscopic observations obtained during five observing runs from 2001 to 2004, we study optical flare events and chromospheric activity variability of the very active RS CVn star UX Ari. By means of the spectral subtraction technique, several optical chromospheric activity indicators （including the He IDa, Na I D1, D2 doublet, Ha and Ca II IRT lines） covered in our echelle spectra were analyzed. Four large optical flare events were detected on UX Ari during our observations, which show prominent He I D3 line emission together with great enhancement in emission of the Ha and Ca II IRT lines and strong filled-in or emission reversal features in the Na ! D1, D2 doublet lines. The newly detected flares are much more energetic than previous discoveries, especially for the flare identified during the 2002 December observing run. Optical flare events on UX Ari are more likely to be observed around two quadratures of the system, except for our optical flares detected during the 2004 November observing run. Moreover, we have found rotational modulation of chromospheric activity in the Ha and Ca II IRT lines, which suggests the presence of chromospherically active longitudes over the surface of UX Ari. The change in chromospherically active longitudes among our observing runs, as well as the variation in chromospheric activity level from 2001 to 2004, indicates a long-term evolution of active regions.
文摘We present the first results of a time-resolved CCD photometric and time-series analysis of NSV 13601,a variable star in the constellation Pegasus.The 14′′Schmidt-Cassegrain telescope of Maharaja Krishnakumarsinhji Bhavnagar University(MKBU)was used for observations.Analysis was performed both in VStar and Period04 software,and their results were compared.The main results are as follows:From data analysis,its has period^77.784 d(MKBU data V)(VStar),~77.632 d(MKBU data Ic)(VStar),~77.058 d(MKBU data V)(Period04)and^49.560 d(MKBU data Ic)(Period04).Its V and I mean magnitudes for MKBU data are 12.203(V)and 11.292(I)mag respectively.We confirm it to be a variable star.
基金supported by the Republic of South Africa's National Research Foundation
文摘A massive star is defined as one with mass greater than - 8-10.M⊙. Central to the on-going debate on how these objects [massive stars] come into being is the so-called Radiation Problem. For nearly forty years, it has been argued that the radiation field emanating from massive stars is high enough to cause a global re- versal of direct radial in-fall of material onto the nascent star. We argue that only in the case of a non-spinning isolated star does the gravitational field of the nascent star overcome the radiation field. An isolated non-spinning star is a non-spinning star without any circumstellar material around it, and the gravitational field beyond its surface is described exactly by Newton＇s inverse square law. The supposed fact that massive stars have a gravitational field that is much stronger than their radiation field is drawn from the analysis of an isolated massive star. In this case the gravitational field is much stronger than the radiation field. This conclusion has been erroneously extended to the case of massive stars enshrouded in gas and dust. We find that, for the case of a non- spinning gravitating body where we take into consideration the circumstellar material, at ,- 8-10M⊙, the radiation field will not reverse the radial in-fall of matter, but rather a stalemate between the radiation and gravitational field will be achieved, i.e. the infall is halted but not reversed. This picture is very different from the common picture that is projected and accepted in the popular literature where at -8-10 M⊙, all the circumstellar material, from the surface of the star right up to the edge of the molec- ular core, is expected to be swept away by the radiation field. We argue that massive stars should be able to start their normal stellar processes if the molecular core from which they form has some rotation, because a rotating core exhibits an Azimuthally Symmetric Gravitational Field which causes there to be an accretion disk and along this equatorial disk. The radiation field cannot be much stronger than the gravitational field, hence this equatorial accretion disk becomes the channel via which the nascent massive star accretes all of its material.
基金Funding for the TESS mission is provided by the NASA Explorer Programsupport of the National Natural Science Foundation of China(NSFC,grant Nos.U2031204,12373038,12163005,and 12288102)+1 种基金the science research grants from the China Manned Space Project with No.CMSCSST-2021-A10the Natural Science Foundation of Xinjiang Nos.2022D01D85 and 2022TSYCLJ0006。
文摘We analyze the frequencies of three known roAp stars,TIC 96315731,TIC 72392575,and TIC 318007796,using the light curves from the Transiting Exoplanet Survey Satellite.For TIC 96315731,the rotational and pulsational frequencies are 0.1498360 day^(-1)and 165.2609 day^(-1),respectively.In the case of TIC 72392575,the rotational frequency is 0.25551 day^(-1).We detect a quintuplet of pulsation frequencies with a center frequency of135.9233 day^(-1),along with two signals within the second pair of rotational sidelobes of the quintuplet separated by the rotation frequency.These two signals may correspond to the frequencies of a dipole mode.In TIC318007796,the rotational and pulsational frequencies are 0.2475021 day^(-1),192.73995 day^(-1),and196.33065 day^(-1),respectively.Based on the oblique pulsator model,we calculate the rotation inclination(i)and magnetic obliquity angle(b)for the stars,which provide the geometry of the pulsation modes.Combining the phases of the frequency quintuplets,the pulsation amplitude and phase modulation curves,and the results of spherical harmonic decomposition,we conclude that the pulsation modes of frequency quintuplets in TIC96315731,TIC 72392575,and TIC 318007796 correspond to distorted dipole mode,distorted quadrupole mode,and distorted dipole mode,respectively.
基金support from the National Natural Science Foundation of China(NSFC,Grant Nos.11403088,11873081,U2031209,11833002,12090040,12090042 and 12003020)partially supported by the Open Project Program of the Key Laboratory of Optical Astronomy,National Astronomical Observatories,Chinese Academy of Sciences。
文摘KIC 10417986 is a short orbital period(0.0737 day)ellipsoidal variable star with aδSct andγDor hybrid pulsation component discovered by Kepler.The ground-based spectroscopic observations were carried out in the winters of 2020 and 2021 to investigate the binary nature of this star.We derive the orbital parameters using the rvfit code with a result of K_(1)=29.7±1.5 km s^(-1),γ=-18.7±1.7 km s^(-1),and confirm an orbital period of 0.84495 day instead of the result given by Kepler.The atmospheric parameters of the primary are determined by the synthetic spectral fitting technique with the estimated values of T_(eff)=7411±187 K,log g=4.2±0.3 dex,[M/H]=0.08±0.09 dex and vsini=52±11 km s^(-1).KIC 10417986 is a circular orbit binary system.From the single-lined nature and mass function of the star,the derived orbital inclination is 26°±6°,and the mass of the secondary is 0.52_(-0.09)^(+0.18)M_(⊙),which should be a late-K to early-M type star.Fourteen frequencies are extracted from Kepler light curves,of which six independent frequencies in the high-frequency region are identified as the p-mode pulsations ofδSct star,and one independent frequency in the low-frequency region(f_(2)=1.3033 cd^(-1))is probably the rotational frequency due to the starspots rather than the ellipsoidal effect.
基金Supported by the National Natural Science Foundation of China
文摘The aim of this paper is to determinate the fundamental parameters of six exoplanet host （EH） stars and their planets. Because techniques for detecting exo- planets yield properties of the planet only as a function of the properties of the host star, we must accurately determine the parameters of the EH stars first. For this rea- son, we constructed a grid of stellar models including diffusion and rotation-induced extra-mixing with given ranges of input parameters （i.e. mass, metallicity and initial rotation rate）. In addition to the commonly used observational constraints such as the effective temperature Tell, luminosity L and metallicity [Fe/H], we added two obser- vational constraints, the lithium abundance log N （Li） and the rotational period Prot. These two additional observed parameters can set further constraints on the model due to their correlations with mass, age and other stellar properties. Hence, our estimations of the fundamental parameters for these EH stars and their planets have a higher preci- sion than previous works. Therefore, the combination of rotational period and lithium helps us to obtain more accurate parameters for stars, leading to an improvement in knowledge about the physical state of EH stars and their planets.
基金supported by the National Natural Science Foundation of China(Grant Nos.11873017 and 11933008)the Science and Technology Talents and Platform Plan of Yunnan province(2018HB070)+1 种基金the Yunnan Natural Science Foundation(No.2018FB006)partially supported by the Open Project Program of the Key Laboratory of Optical Astronomy,National Astronomical Observatories,Chinese Academy of Sciences。
文摘IO Cnc was classified to be a new G-type(G0)W UMa-type eclipsing binary system.Our first multicolor photometric solutions show that IO Cnc is a new W-subtype shallow contact binary with a fill-out factor of f=16.1%and a low mass ratio of q=3.12(or 1/q=0.32).During orbital period investigations,a cyclic variation and a downward parabolic variation with a rate of(-1.28±0.43)×10^(-7) d yr^(-1) was discovered in the observed–calculated(O-C)curve.The cyclic variation was analyzed by the light travel time effect(LTTE)via a potential red dwarf companion star,an orbital semi-major axis shorter than 4.88±0.82 AU was obtained.Finally,we collect physical parameters of a sample of 50 G-type shallow contact binaries(f≤20%),it is suggested that most of the G-type shallow contact binaries are undergoing a longterm and periodic orbital period changes,especially more systems show long-term decreases.The long-term orbital period decrease indicates that IO Cnc is in a mass transferring from the more massive component to the less massive one.With the long-term decrease of the orbital period,this shallow contact binary will evolve into a deeper contact one.
