Galaxies最新文献_第9页

Spiral Galaxies 螺旋星系

IF 2.5

Galaxies Pub Date : 2023-02-24 DOI: 10.1002/9781119818007.ch4

F. Combes

引用次数: 6

New Method to Detect and Characterize Active Be Star Candidates in Open Clusters 探测和表征开放星团中活跃Be星候选者的新方法

IF 2.5

Galaxies Pub Date : 2023-02-19 DOI: 10.3390/galaxies11010037

A. Granada, Maziar R. Ghoreyshi, Carol E. Jones, T. Eenmäe

引用次数: 0

Recent Progress in Finding Binary Systems with the B[e] Phenomenon 用B[e]现象寻找双星系统的新进展

IF 2.5

Galaxies Pub Date : 2023-02-17 DOI: 10.3390/galaxies11010036

A. Miroshnichenko, S. Zharikov, N. Manset, S. Khokhlov, A. S. Nodyarov, V. Klochkova, S. Danford, Aizhan K. Kuratova, R. Mennickent, S. Chojnowski, A. Raj, D. Bisht

{"title":"Recent Progress in Finding Binary Systems with the B[e] Phenomenon","authors":"A. Miroshnichenko, S. Zharikov, N. Manset, S. Khokhlov, A. S. Nodyarov, V. Klochkova, S. Danford, Aizhan K. Kuratova, R. Mennickent, S. Chojnowski, A. Raj, D. Bisht","doi":"10.3390/galaxies11010036","DOIUrl":"https://doi.org/10.3390/galaxies11010036","url":null,"abstract":"This paper describes recent studies of the FS CMa-type objects, a group of stars showing the B[e] phenomenon defined in 2007. The objects exhibit strong emission-line spectra with both permitted and forbidden lines suggesting the presence of a B-type star as well as strong IR excesses due to radiation of circumstellar dust. These properties are hard to explain in the framework of the evolution of single stars with luminosities between ~300 and ~30,000 L⊙ typical of most B-type stars. We explore the hypothesis that the gaseous-and-dusty envelopes of FS CMa objects are due to either earlier or ongoing mass transfer between the binary system components. It is hard to detect the secondary components in these systems because of veiling and distortions by the circumstellar matter because of the relative faintness of the companions. Nevertheless, we detected regular radial velocity variations of the spectral lines in MWC 728, 3 Pup, and AS 386 and we found absorption lines typical of cool stars in the spectra of MWC 645, AS 174, and several other objects. The diversity of the secondary components in FS CMa objects is discussed in the context of non-conservative binary evolution.","PeriodicalId":37570,"journal":{"name":"Galaxies","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2023-02-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44359209","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 2

Primordial Black Hole Formation in Non-Standard Post-Inflationary Epochs 非标准后暴胀时期的原始黑洞形成

IF 2.5

Galaxies Pub Date : 2023-02-16 DOI: 10.3390/galaxies11010035

S. Bhattacharya

{"title":"Primordial Black Hole Formation in Non-Standard Post-Inflationary Epochs","authors":"S. Bhattacharya","doi":"10.3390/galaxies11010035","DOIUrl":"https://doi.org/10.3390/galaxies11010035","url":null,"abstract":"When large overdensities gravitationally collapse in the early universe, they lead to primordial black holes (PBH). Depending on the exact model of inflation leading to necessary large perturbations at scales much smaller than scales probed at the Cosmic Microwave Background (CMB) surveys, PBHs of masses ≲103M⊙ are formed sometime between the end of inflation and nucleosynthesis. However, the lack of a direct probe for the exact expansion history of the universe in this duration introduces uncertainties in the PBH formation process. The presence of alternate cosmological evolution for some duration after inflation affects the relation between (i) PBH mass and the scale of the collapsing overdensity; and (ii) PBH abundance and amplitude of the overdensities. In this review, the non-standard cosmological epochs relevant for a difference in PBH production are motivated and discussed. The importance of developing the framework of PBH formation in non-standard epochs is discussed from a phenomenological point of view, with particular emphasis on the advances in gravitational wave (GW) phenomenology, since abundant PBHs are always accompanied by large induced GWs. PBH formation in general non-standard epochs is also reviewed including the mathematical formalism. Specific examples, such as PBH formation in a kinetic energy dominated epoch and an early matter dominated epoch, are discussed with figures showing higher PBH abundances as compared to the production in standard radiation domination.","PeriodicalId":37570,"journal":{"name":"Galaxies","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2023-02-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41412458","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 6

The Next Generation Event Horizon Telescope Collaboration: History, Philosophy, and Culture 下一代事件视界望远镜合作：历史、哲学和文化

IF 2.5

Galaxies Pub Date : 2023-02-15 DOI: 10.3390/galaxies11010032

P. Galison, Juliusz Doboszewski, Jamee Elder, N. C. Martens, A. Ashtekar, Jonas Enander, Marie Gueguen, Elizabeth A. Kessler, R. Lalli, Martin Lesourd, A. Marcoci, Sebastián Murgueitio Ramírez, P. Natarajan, James Nguyen, Luis Reyes-Galindo, Sophie Ritson, Mike D. Schneider, Emilie Skulberg, Helene Sorgner, M. Stanley, A. Thresher, J. van Dongen, J. Weatherall, Jingyi Wu, A. Wüthrich

引用次数: 4

Transverse Oscillations of the M87 Jet Revealed by KaVA Observations KaVA观测揭示M87喷流的横向振荡

IF 2.5

Galaxies Pub Date : 2023-02-15 DOI: 10.3390/galaxies11010033

H. Ro, K. -H. Yi, Yuzhu Cui, M. Kino, K. Hada, T. Kawashima, Y. Mizuno, B. Sohn, F. Tazaki

{"title":"Transverse Oscillations of the M87 Jet Revealed by KaVA Observations","authors":"H. Ro, K. -H. Yi, Yuzhu Cui, M. Kino, K. Hada, T. Kawashima, Y. Mizuno, B. Sohn, F. Tazaki","doi":"10.3390/galaxies11010033","DOIUrl":"https://doi.org/10.3390/galaxies11010033","url":null,"abstract":"Recent VLBI monitoring has found transverse motions of the M87 jet. However, due to the limited cadence of previous observations, details of the transverse motion have not been fully revealed yet. We have regularly monitored the M87 jet at KVN and VERA Array (KaVA) 22 GHz from December 2013 to June 2016. The average time interval of the observation is ∼0.1 year, which is suitable for tracking short-term structural changes. From these observations, the M87 jet is well represented by double ridge lines in the region 2–12 mas from the core. We found that the ridge lines exhibit transverse oscillations in all observed regions with an average period of 0.94±0.12 years. When the sinusoidal fit is performed, we found that the amplitude of this oscillation is an order of ∼0.1 mas, and the oscillations in the northern and southern limbs are almost in phase. Considering the amplitude, it does not originate from Earth’s parallax. We propose possible scenarios of the transverse oscillation, such as the propagation of jet instabilities or magneto-hydrodynamic (MHD) waves or perturbed mass injection around magnetically dominated accretion flows.","PeriodicalId":37570,"journal":{"name":"Galaxies","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2023-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46553272","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 1

Reddening-Free Q Parameters to Classify B-Type Stars with Emission Lines 重定自由Q参数对具有发射线的B型星进行分类

IF 2.5

Galaxies Pub Date : 2023-02-15 DOI: 10.3390/galaxies11010031

Y. Aidelman, L. Cidale

{"title":"Reddening-Free Q Parameters to Classify B-Type Stars with Emission Lines","authors":"Y. Aidelman, L. Cidale","doi":"10.3390/galaxies11010031","DOIUrl":"https://doi.org/10.3390/galaxies11010031","url":null,"abstract":"The emission-line B-type stars constitute a heterogeneous group. Many of these stars show similar optical spectroscopic features and color indices, making it difficult to classify them adequately by means of photometric and spectroscopic techniques. Thus, it is relevant to deal with appropriate classification criteria to avoid as many selection effects as possible. For this purpose, we analyzed different reddening-free Q parameters, taking advantage of the Gaia and 2MASS photometric surveys, for both main sequence and emission-line B-type stars. Along with this work, we provided various criteria to search for normal and emission-line B-type stars, using different color–color, Q–color, and Q–Q diagrams. It was also possible to identify stars in different transition phases (i.e., (Rp−J) vs. (J−Ks) diagrams) and to classify them according to their NIR radiation excesses (i.e., the (Bp−Rp) vs. (H−Ks) diagram). Other diagrams, such as the QJKHK vs. (H−Ks) or QBpJHK vs. (Bp−Ks), were very useful to search for and classify different classes of B-type stars with emission lines. These diagrams highlighted the presence of several stars, classified as CBe, with large color excesses that seemed to be caused by the presence of dust in their envelopes. Therefore, these stars would be misclassified. Three groups of HAeBe stars with different intrinsic dust properties were also distinguished. The amount of intrinsic dust emission in the diverse groups of emission-line stars was well-recognized via the QJHK vs. QBpRpHK diagram. The different selection criteria are very important tools for automated designs of machine learning and optimal search algorithms.","PeriodicalId":37570,"journal":{"name":"Galaxies","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2023-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42378709","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

HINOTORI and Its Perspectives in the Black-Hole Jet Study HINOTORI及其在黑洞喷流研究中的前景

IF 2.5

Galaxies Pub Date : 2023-02-13 DOI: 10.3390/galaxies11010030

Toshihisa Tsutsumi, K. Niinuma, H. Imai, Ryoko Amari, Y. Shimizu, H. Ogawa, Atsushi Nishimura, C. Miyazawa, T. Oyama, Hiroyuki Kaneko, K. Nakashima, S. Sawada-Satoh, T. Aoki

{"title":"HINOTORI and Its Perspectives in the Black-Hole Jet Study","authors":"Toshihisa Tsutsumi, K. Niinuma, H. Imai, Ryoko Amari, Y. Shimizu, H. Ogawa, Atsushi Nishimura, C. Miyazawa, T. Oyama, Hiroyuki Kaneko, K. Nakashima, S. Sawada-Satoh, T. Aoki","doi":"10.3390/galaxies11010030","DOIUrl":"https://doi.org/10.3390/galaxies11010030","url":null,"abstract":"Simultaneous multi-band very long baseline interferometry (VLBI) observations at millimeter wavelengths have huge potential for various science cases. However, there exist difficulties in expanding the scientific targets, as the sensitivity of radio telescopes at millimeter wavelengths is typically lower compared to that at centimeter wavelengths. In order to realize high-sensitivity mm-VLBI observations in the East Asia region, we are promoting the HINOTORI (Hybrid Installation project in NObeyama, Triple-band ORIented) project, which aims to launch the wide-band and simultaneous triple-band (22/43/86 GHz) VLBI system with the Nobeyama 45 m Radio Telescope (NRO45). The simultaneous 22/43 GHz observation mode has already been operated for the open-use program. We have recently completed the performance evaluation of the receiver and observing system at 86 GHz. In addition, a new wide-band VLBI back-end system has been installed on the NRO45 and the performance of this receiving system has been found to be sufficient to meet scientific requirements. Currently, we are performing commissioning observations to establish regular VLBI operation with simultaneous triple-band mode together with the Korean VLBI Network. The participation of the NRO45 is expected to strengthen the mm-VLBI observation network in the East Asia region and to be a very powerful addition with respect to the science of of black hole jets.","PeriodicalId":37570,"journal":{"name":"Galaxies","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2023-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47514223","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 1

Jet Feedback in Star-Forming Galaxies 恒星形成星系中的喷流反馈

IF 2.5

Galaxies Pub Date : 2023-02-12 DOI: 10.3390/galaxies11010029

M. Krause

引用次数: 1

Enabling Transformational ngEHT Science via the Inclusion of 86 GHz Capabilities 通过包含86 GHz功能实现变革性夜间科学

IF 2.5

Galaxies Pub Date : 2023-02-10 DOI: 10.3390/galaxies11010028

S. Issaoun, D. Pesce, F. Roelofs, A. Chael, R. Dodson, M. Rioja, K. Akiyama, Romy Aran, L. Blackburn, S. Doeleman, V. Fish, Garret Fitzpatrick, Michael D. Johnson, G. Narayanan, Alexander W. Raymond, R. Tilanus

{"title":"Enabling Transformational ngEHT Science via the Inclusion of 86 GHz Capabilities","authors":"S. Issaoun, D. Pesce, F. Roelofs, A. Chael, R. Dodson, M. Rioja, K. Akiyama, Romy Aran, L. Blackburn, S. Doeleman, V. Fish, Garret Fitzpatrick, Michael D. Johnson, G. Narayanan, Alexander W. Raymond, R. Tilanus","doi":"10.3390/galaxies11010028","DOIUrl":"https://doi.org/10.3390/galaxies11010028","url":null,"abstract":"We present a case for significantly enhancing the utility and efficiency of the ngEHT by incorporating an additional 86 GHz observing band. In contrast to 230 or 345 GHz, weather conditions at the ngEHT sites are reliably good enough for 86 GHz to enable year-round observations. Multi-frequency imaging that incorporates 86 GHz observations would sufficiently augment the (u,v) coverage at 230 and 345 GHz to permit detection of the M87 jet structure without requiring EHT stations to join the array. The general calibration and sensitivity of the ngEHT would also be enhanced by leveraging frequency phase transfer techniques, whereby simultaneous observations at 86 GHz and higher-frequency bands have the potential to increase the effective coherence times from a few seconds to tens of minutes. When observation at the higher frequencies is not possible, there are opportunities for standalone 86 GHz science, such as studies of black hole jets and spectral lines. Finally, the addition of 86 GHz capabilities to the ngEHT would enable it to integrate into a community of other VLBI facilities—such as the GMVA and ngVLA—that are expected to operate at 86 GHz but not at the higher ngEHT observing frequencies.","PeriodicalId":37570,"journal":{"name":"Galaxies","volume":" ","pages":""},"PeriodicalIF":2.5,"publicationDate":"2023-02-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44676053","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 5