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Journal articles on the topic 'Variable stars'

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Author: Grafiati

Published: 4 June 2021

Last updated: 29 July 2024

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1

Szeidl, B., M. Breger, A. N. Cox, R. E. Gershberg, M. Jerzykiewicz, L. N. Mavridis, L. N. Mirzoyan, et al. "27. Variable Stars (Etoiles Variables)." Transactions of the International Astronomical Union 20, no. 1 (1988): 257–92. http://dx.doi.org/10.1017/s0251107x00007197.

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The field of variable star research has become so broad and the amount of research to be reported on has grown so rapidly that it is a vain hope that a report of this kind, in a very limited space, could cover the whole field of research and could mention all the papers that have been published in the last three years. It is only hoped that this report presents the significant results achieved in the field of the most important aspects of variable star research. Some important subjects (e.g. cataclysmic variables) relevant to the variable star research are reviewed in the reports of other commissions. This is a consequence of the fact that the research has become very complex and the phenomena producing light variability belong to the field of interest of other commissions, too.

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2

Percy, J. R., L. Szabados, K. Oláh, N. N. Samus, Luis A. Balona, D. W. Kurtz, Nancy Remage Evans, et al. "27. Variable Stars (Etoiles Variables)." Transactions of the International Astronomical Union 22, no. 1 (1994): 243–76. http://dx.doi.org/10.1017/s0251107x00008051.

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3

Jerzykiewicz, M., L. A. Baiona, E. F. Guinan, Y. Kondo, D. W. Kurtz, M. Rodono, and J. Sahade. "Division V: Variable Stars: (Etoiles Variables)." Transactions of the International Astronomical Union 24, no. 1 (2000): 251–54. http://dx.doi.org/10.1017/s0251107x0000314x.

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This report covers the period July 1, 1996 (the closing date of the reports in the IAU Trans. 23A) through August 31, 1999. Since the reports of Commissions 27 and 42 that follow highlight the research made in the triennium, we limit ourselves here to organizational activities of the Division. The first three sections are devoted to the General Catalogue of Variable Stars (GCVS), the Information Bulletin on Variable Stars (IBVS), and the Archives of Unpublished Observations of Variable Stars, the important projects that serve us all. I am indebted to the authors, listed in the sections headings, for providing these summaries. The problems of naming and classifying variable stars, implicit in Sect. 2, are taken up in Sect. 5. The last section lists meetings sponsored by the Division.

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4

Guinan, Edward F., S. Balona, J. Christensen-Dalgaard, M. Jerzykiewicz, D. Kurtz, J. Sahade, and P. Szkody. "Division V: Variable Stars: (Etoiles Variables)." Transactions of the International Astronomical Union 25, no. 1 (2002): 265–67. http://dx.doi.org/10.1017/s0251107x00001528.

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5

Christensen-Dalsgaard, Jørgen, Conny Aerts, Carla Cacciari, Peter Cottrell, Ed Guinan, Petr Harmanec, Don Kurtz, et al. "Commission 27: Variable Stars: (Etoiles Variables)." Transactions of the International Astronomical Union 25, no. 1 (2002): 271–76. http://dx.doi.org/10.1017/s0251107x00001553.

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6

Percyy, John R. "Variable stars." Physics Teacher 31, no. 9 (December 1993): 541–43. http://dx.doi.org/10.1119/1.2343874.

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7

Kurtz, D. W., J. Christensen-Dalsgaard, C. Cacciari, P. Cottrell, P. Harmanec, M. Jerzykiewicz, J. Matthews, P. Moskalik, D. Sasselov, and D. Welch. "Commission 27: Variable Stars: (Les Etoiles Variables)." Transactions of the International Astronomical Union 24, no. 1 (2000): 255–58. http://dx.doi.org/10.1017/s0251107x00003151.

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For Commission 27 these triennial reports have traditionally been very compact literature reviews of all the fields relevant to our commission. For several triennia we have been discussing the relevance of them, and asking just who their readership is. It seems that only a few people read them, and fewer use them as introductions to the subject – supposedly one of their prime purposes. The major beneficiaries have been the writers, who have been forced to do three-year reviews of their subjects. The IAU EC gave us the option this triennium of a shorter, four-page report to which the majority of the SOC agreed.

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8

Christensen-Dalsgaard, Jørgen. "Commission 27: Variable Stars (Les Étoiles Variables)." Transactions of the International Astronomical Union 25, no. 2 (2007): 149–50. http://dx.doi.org/10.1017/s0251107x00026705.

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9

Warner, Brian. "Cataclysmic Variable Stars." Highlights of Astronomy 11, no. 1 (1998): 16–27. http://dx.doi.org/10.1017/s1539299600019924.

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The evolution of single stars on and away from the main sequence is well understood. A degenerate core is formed in a star as the star leaves the main sequence and expands to a giant with a radius typically 50 - 500 Ro . Observationally it is known that most stars are members of binary systems, and among these many have orbital periods less than 100 y. It can happen, therefore, that the expanding envelope of the primary of a binary system can reach to the secondary. As this happens, the primary fills its Roche tidal lobe and transfers matter to the secondary; if the primary has a radiative envelope the rate at which this occurs exceeds the Eddington limit of the secondary, which therefore repels the incoming gas, forming a common envelope around the two stars. Friction within the envelope causes the stars to spiral towards each other until the energy and angular momentum extracted from the binary orbit and transferred to the envelope are sufficient to eject the common envelope as a planetary nebula, leaving a short period binary comprising a white dwarf and a main sequence star.This mechanism of producing short period binaries containing white dwarfs, proposed by Ostriker and by Paczynski (1976), is the probable origin of the class of objects known as Cataclysmic Variable Stars (CVs), which encompass the classical novae, dwarf novae, novalike variables and a variety of related objects. Evidence has been accumulating for forty years (Crawford & Kraft 1956, Warner 1995a) that every CV consists of a secondary star (usually a dwarf, but a few systems contain giants) filling its Roche lobe and transferring mass to a white dwarf primary. In systems of normal chemical composition the orbital periods lie between 75 mins and ~250 d, with the majority having . A few hydrogen-free systems are known for which 17 mins < Porb < 50 mins. It should be noted that CVs are very compact binary systems: for h such a binary would fit inside the Sun.

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10

Baker, N., B. Szeidl, M. Breger, A. N. Cox, J. D. Fernie, A. M. van Genderen, R. E. Gershberg, et al. "27. Variable Stars." Transactions of the International Astronomical Union 19, no. 1 (1985): 277–311. http://dx.doi.org/10.1017/s0251107x00006398.

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The field of variable-star research is so broad that no report of this nature could possibly mention all the papers that have appeared in the last three years. It is hoped, however, that the reviews below include the most important work and identify the most significant trends. This report comprises ten sections on as many different research topics, each written by a different member of Commission 27. In addition there are (in Section 12) three short reports about ongoing activities of the commission. The commission president is very grateful to the authors of the individual contributions who have worked so conscientously.

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11

Warner, Brian, and Scott Kenyon. "Cataclysmic Variable Stars." Physics Today 49, no. 11 (November 1996): 88–89. http://dx.doi.org/10.1063/1.881529.

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12

Kudashkina, L. S. "Semiregular Variable Stars." Astrophysics 62, no. 4 (November 28, 2019): 556–72. http://dx.doi.org/10.1007/s10511-019-09604-4.

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13

Burnashev, V. I., and B. A. Burnasheva. "Edward Schoenfeld: Visual photometry of variable stars. 2. Variable stars." Bulletin of the Crimean Astrophysical Observatory 105, no. 1 (June 2009): 78–81. http://dx.doi.org/10.3103/s0190271709010100.

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14

Zhou, Ai-Ying. "Identifying SuperWASP Detected Candidate Variables with TESS*." Research Notes of the AAS 7, no. 10 (October 27, 2023): 227. http://dx.doi.org/10.3847/2515-5172/ad06b9.

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Abstract Using Transiting Exoplanet Survey Satellite light curves, I have identified more than 1200 new pulsating variable stars from the SuperWASP-detected but unclassified candidate variables. These include a variety of types of pulsating variable stars, including 125 δ Scuti stars, 235 γ Doradus stars, 302 RR Lyrae stars, and 450+ Mira/SR/IR/LPV variables. I also identified 1300+ rotating variable stars. Additionally, I revealed that 16 of 91 newly identified eclipsing binary systems have pulsating components. These findings will help us to better understand the properties and evolution of pulsating variable stars.

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15

Morris, S. L. "The ellipsoidal variable stars." Astrophysical Journal 295 (August 1985): 143. http://dx.doi.org/10.1086/163359.

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16

Christensen-Dalsgaard, Jørgen, Alvaro Giménez, Edward F. Guinan, Conny Aerts, Luis A. Balona, and Jorge Sahade. "DIVISION V: VARIABLE STARS." Proceedings of the International Astronomical Union 3, T26B (December 2007): 165–67. http://dx.doi.org/10.1017/s1743921308023946.

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Division V provides a joint forum for the study of stellar variability in all its manifestations, whether due to pulsation, surface inhomogeneities, evolutionary changes, or to eclipses and other phenomena specifically related to double and multiple stars.

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17

Aerts, Conny, Steven D. Kawaler, Jørgen Christensen-Dalsgaard, Timothy R. Bedding, Carla Cacciari, Peter L. Cottrell, Margarida Cunha, et al. "COMMISSION 27: VARIABLE STARS." Proceedings of the International Astronomical Union 3, T26B (December 2007): 168–70. http://dx.doi.org/10.1017/s1743921308023958.

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The meeting started at 16h00. The president welcomed the 24 participants to the business meeting of Commission 27. After the approval of the agenda, she gave an overview of the activities of Commission 27 of the past three years.

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18

Giménez, Alvaro, Steven D. Kawaler, Conny Aerts, Jørgen Christensen-Dalsgaard, Michael Breger, Edward F. Guinan, Donald W. Kurtz, and Slavek M. Rucinski. "DIVISION V: VARIABLE STARS." Proceedings of the International Astronomical Union 4, T27A (December 2008): 251–53. http://dx.doi.org/10.1017/s1743921308025623.

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Division V deals with all aspects of stellar variability, either intrinsic or due to eclipses by its companion in a binary system. In the case of intrinsic stellar variability the analysis of pulsating stars, surface inhomogeneities, stellar activity and oscillations are considered. For close binaries, classical detached eclipsing binaries are studied as well as more interacting systems, like contact and semi-detached binaries, or those with compact components, like cataclysmic variables and X-ray binaries, including the physics of accretion processes.

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19

Kawaler, Steven D., Gerald Handler, Conny Aerts, Timothy R. Bedding, Márcio Catelán, Margarida Cunha, Laurent Eyer, et al. "COMMISSION 27: VARIABLE STARS." Proceedings of the International Astronomical Union 4, T27A (December 2008): 254–59. http://dx.doi.org/10.1017/s1743921308025635.

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The Organizing Committee of Commission 27 has decided to again provide a somewhat abbreviated bibliography as part of this triennial report, as astronomy-centered search engines and on-line publications continue to blossom. We focus on selected highlights in variable star research over the past three years. Further results can be found in numerous proceedings of conferences held in the time frame covered by this report.

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20

Christensen-Dalsgaard, Jørgen, Conny Aerts, Alvaro Giménez, Edward F. Guinan, Luis A. Balona, and Jorge Sahade. "Division V: Variable Stars." Proceedings of the International Astronomical Union 1, T26A (December 2005): 245. http://dx.doi.org/10.1017/s1743921306004637.

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Division V, “Variable Stars”, consists of Commission 27, also called “Variable Stars” and Commission 42, “Close Binaries”. Thus the former deals with stars whose variations are intrinsic, whereas in the latter the variations are caused by the interactions between the components in the binary. It is evident that the definition of the Division is predominantly observational, and there may be cases where the assignment of an object to one of the two commissions might be in doubt (a recent somewhat related example was the first detection of an extra-solar planet, in 54 Pegasi, where intrinsic variability of the star in the form of high-order g modes was also initially suspected).

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21

Aerts, Conny, Steven Kawaler, Tim Bedding, Carla Cacciari, Jørgen Christensen-Dalsgaard, Peter Cottrell, Margarida Cunha, et al. "Commission C27: Variable Stars†." Proceedings of the International Astronomical Union 1, T26A (December 2005): 247–58. http://dx.doi.org/10.1017/s1743921306004649.

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AbstractWe report the major highlights of variable star research within the past three years. This overview is limited to intrinsically variable stars, because the achievements in variable star research stemming from binarity, or multiplicity in general, is covered by the summary report of Commissions 26 and 42.

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22

Gimenez, Alvaro, Steven Kawaler, Jørgen Christensen-Dalsgaard, Michel Breger, Edward Guinan, and Slavek Rucinski. "DIVISION V: VARIABLE STARS." Proceedings of the International Astronomical Union 6, T27B (May 14, 2010): 207–8. http://dx.doi.org/10.1017/s1743921310005107.

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Division V organized a brief Business meeting during the XXVIIth General Assembly, prior to Business meetings (reported separately) of Commissions 27 and 42. The Division V Business Meeting began at 11:00 on 5 August 2009.

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23

Kawaler, Steven D., Gerald Handler, Conny Aerts, Tim Bedding, Márcio Catelan, Margarida Cunha, Laurent Eyer, et al. "COMMISSION 27: VARIABLE STARS." Proceedings of the International Astronomical Union 6, T27B (May 14, 2010): 209–10. http://dx.doi.org/10.1017/s1743921310005119.

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The meeting started at 14h00. The president welcomed the participants to the business meeting of C27, and acknowledged the members of the Organizing Committee. Special thanks were expressed to the outgoing members: Conny Aerts, Peter Martinez, and Seetha Somasundaram.

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24

Kawaler, Steven D., Ignasi Ribas, Alvaro Gimenez, Michel Breger, Edward F. Guinan, Gerald Handler, and Slavek M. Rucinski. "DIVISION V: VARIABLE STARS." Proceedings of the International Astronomical Union 7, T28A (December 2011): 211–12. http://dx.doi.org/10.1017/s1743921312002839.

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25

Handler, Gerald, Karen R. Pollard, Steven Kawaler, Margarida S. Cunha, Katalin Olah, Katrien Kolenberg, C. Simon Jeffery, et al. "COMMISSION 27: VARIABLE STARS." Proceedings of the International Astronomical Union 7, T28A (December 2011): 213–18. http://dx.doi.org/10.1017/s1743921312002840.

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26

Eyer, Laurent, Berry Holl, and Nami Mowlavi. "Gaia and variable stars." Proceedings of the International Astronomical Union 9, S298 (May 2013): 265–68. http://dx.doi.org/10.1017/s1743921313006455.

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AbstractThe study of variable phenomena (periodic, irregular or transient) provides a unique way to acquire knowledge about objects in our Universe. Currently, we are going through a rapid expansion of time-domain astrophysics. One reason for this expansion is the technological developments materialised in small to medium size observational projects such as HAT, OGLE, Catalina, PTF and upcoming very large projects such as Gaia or LSST.In this article, we are focusing on the ESA cornerstone mission Gaia. This spacecraft will provide astrometric, photometric and spectroscopic measurements for one billion stars. Among the existing and planned multi-epoch projects Gaia is unique because it will provide exquisite astrometric measurements for all objects it observes. We provide a brief overview of the literature concerning this mission and its expected contribution to variability studies.

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27

Ahmad Dar, Ajaz, Padmakar Singh Parihar, Parvej Saleh, and Manzoor Ahmad Malik. "Variable stars in M37." Research in Astronomy and Astrophysics 18, no. 12 (December 2018): 155. http://dx.doi.org/10.1088/1674-4527/18/12/155.

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28

Kazarian, M. A., and G. V. Petrosian. "Three New Variable Stars." Astrophysics 46, no. 4 (October 2003): 502–5. http://dx.doi.org/10.1023/b:asys.0000003266.19893.37.

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29

Michalska, Gabriela. "Variable stars in young open cluster NGC 2244." Monthly Notices of the Royal Astronomical Society 487, no. 3 (June 3, 2019): 3505–22. http://dx.doi.org/10.1093/mnras/stz1500.

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ABSTRACT We present results of a UBVIC variability survey in the young open cluster NGC 2244. In total, we found 245 variable stars. Most of them, 211 stars, are variables with irregular variations. Furthermore, 23 periodic variables were found. We also detected four candidates for δ Scuti stars and seven eclipsing binaries. Based on the mid-infrared Spitzer and WISE photometry and near infrared JHKS 2MASS photometry, we classified 104 young stellar sources among our variables: 1 Class I object, 1 Class I/flat spectrum object, 4 flat spectrum objects, 91 Class II objects, and 7 transition disc objects. This classification, together with r′i′Hα IPHAS photometry and JHK UKIDSS photometry, were used for identification of pre-main sequence stars among irregular and periodic variables. In this way, 97 CTTS candidates (96 irregular and one periodic variable), 68 WTTS candidates (54 irregular and 14 periodic variables), and 6 Herbig Ae/Be stars were found. For 223 variable stars we calculated membership probability based on proper motions from Gaia DR2 catalogue. Majority of them, 143 stars, are cluster members with probability greater than 70 per cent. For only 36 variable stars the membership probability is smaller than 20 per cent.

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30

Maurya, Jayanand, Y. C. Joshi, A. Panchal, and A. S. Gour. "Investigating Stellar Variability in the Open Cluster Region NGC 381." Astronomical Journal 165, no. 3 (February 8, 2023): 90. http://dx.doi.org/10.3847/1538-3881/acad7e.

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Abstract We study variable stars in the field of the open cluster NGC 381 using photometric data observed over 27 nights and identify a total of 57 variable stars, six of which are member stars. The variable stars are classified based on their periods, amplitudes, light-curve shapes, and locations in the H-R diagram. We found a rich variety of variable stars in the cluster. We identified a total of 10 eclipsing binaries, of which two are of Algol type while eight are of W UMa type (EW). The estimated ages of these EW binaries are greater than 0.6 Gyr, which is in agreement with the formation time constraint of ≥0.6 Gyr on short-period eclipsing binaries. The physical parameters of the two EW-type binaries are estimated using PHOEBE model-fitting software. The pulsating variable stars include one each from the δ Scuti and γ Dor variability classes. We determined the pulsation modes of pulsating variables with the help of the FAMIAS package. We obtained 15 rotational variable stars comprising four dwarf stars identified on the basis of their log(g) versus log(T eff) diagram. These dwarf stars are found to have generally longer periods than the remaining rotational variables.

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31

Goldsmith, C. G. "Variable Stars in the Sculptor Dwarf Galaxy." International Astronomical Union Colloquium 139 (1993): 358. http://dx.doi.org/10.1017/s025292110011783x.

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This project was initiated in 1985 by James Nemec (University of Washington) and Nicholas Suntzeff (C.T.I.O.). The goal was to study the system of ∼600 variable stars in the Sculptor dwarf galaxy. In 1987 the author became the recipient of the plate collection, which formed the basis for his Ph.D. dissertation. In this paper preliminary results are presented. Briefly, 612 stars were studied, of which 432 are van Agt (1978) stars and 180 are newly discovered variable stars. A total of 381 stars are confirmed variables. Most of these are RR Lyraes, but many anomalous Cepheids and some candidate eclipsing variables were also found. Several candidate double-mode RR Lyrae stars were also identified. The mean period of the ab-type RR Lyrae stars is 0.60±0.08 day, and the mean period of the c-type stars is 0.35±0.03 day, not unlike the mean periods of other nearby dwarf galaxies.

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32

Wang, Hong, Yu Zhang, Xiangyun Zeng, Qingshun Hu, Jinzhong Liu, Mingfeng Qin, and Guoliang Lü. "Searching for Variable Stars in the Open Cluster NGC 2355 and Its Surrounding Region." Astronomical Journal 164, no. 2 (July 7, 2022): 40. http://dx.doi.org/10.3847/1538-3881/ac755a.

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Abstract We have investigated the variable stars in the field surrounding NGC 2355 based on the time-series photometric observation data. More than 3000 CCD frames were obtained in the V band spread over 13 nights with the Nanshan One-meter Wide-field Telescope. We have detected 88 variable stars, containing 72 new variable stars and 16 known variable stars. By analyzing these light curves, we classified the variable stars as follows: 26 eclipsing binaries, 52 pulsating stars, four rotating variables, and six unclear type-variable stars for which their periods are much longer than the time baseline chosen. Employing Gaia DR2 parallax, kinematics, and photometry, the cluster memberships of these variable stars were also analyzed for NGC 2355. In addition to the 11 variable members reported by Cantat-Gaudin et al. (2018), we identify four more variable member candidates located at the outer region of NGC 2355 and showed homogeneity in space positions and kinematic properties with the cluster members. The main physical parameters of NGC 2355 estimated from the two-color and color–magnitude diagrams are log(age/yr) = 8.9, E(B − V) = 0.24 mag, and [Fe/H] = −0.07 dex.

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33

Shipman, H. L. "Variable white dwarfs." Proceedings of the International Astronomical Union 15, S357 (October 2019): 107–9. http://dx.doi.org/10.1017/s1743921320001386.

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AbstractAsteroseismology of white dwarf stars has led to a number of interesting results pertaining to the long term evolution and present state of white dwarf interiors. I will review recent results and will give a not necessarily comprehensive view of the prospects for further progress in this area. Two – but only two white dwarf stars - have shown the expected cooling as they age. Careful observations of a few white dwarfs with rich pulsational properties reveal interior compositions as well as the thickness of their surface layers. A few very well observed stars have revealed changes in their pulsational spectra which we don’t understand yet.

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34

Bernhard, Klaus, Stefan Hümmerich, Ernst Paunzen, and Johana Supíková. "New magnetic chemically peculiar stars and candidates in the ATLAS first catalogue of variable stars." Monthly Notices of the Royal Astronomical Society 506, no. 3 (July 20, 2021): 4561–77. http://dx.doi.org/10.1093/mnras/stab2065.

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ABSTRACT The number of known variable stars has increased by several magnitudes over the last decade, and automated classification routines are becoming increasingly important to cope with this development. Here we show that the ‘upside-down CBH variables’, which were proposed as a potentially new class of variable stars by Heinze et al. in the ATLAS First Catalogue of Variable Stars, are, at least to a high percentage, made up of α2 Canum Venaticorum (ACV) variables – that is, photometrically variable magnetic chemically peculiar (CP2/He-peculiar) stars – with distinct double-wave light curves. Using suitable selection criteria, we identified 264 candidate ACV variables in the ATLAS variable star catalogue. 62 of these objects were spectroscopically confirmed with spectra from the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (all new discoveries except for nine stars) and classified on the MK system. The other 202 stars are here presented as ACV star candidates that require spectroscopic confirmation. The vast majority of our sample of stars are main-sequence objects. Derived masses range from 1.4 M⊙ to 5 M⊙, with half our sample stars being situated in the range from 2 M⊙ to 2.4 M⊙, in good agreement with the spectral classifications. Most stars belong to the thin or thick disc; four objects, however, classify as members of the halo population. With a peak magnitude distribution at around 14th magnitude, the here presented stars are situated at the faint end of the known Galactic mCP star population. Our study highlights the need to consider rare variability classes, like ACV variables, in automated classification routines.

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35

Samus, Nikolay N., Elena V. Kazarovets, and Olga V. Durlevich. "Catalogs of variable stars, current and future." Proceedings of the International Astronomical Union 5, S264 (August 2009): 496–98. http://dx.doi.org/10.1017/s174392130999319x.

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AbstractTo study effects of stellar variability, it is necessary to have complete lists of variable stars with good coordinates, correct variability ranges, reliable classification. The General Catalogue of Variable Stars (GCVS) is one of the main sources of information of this kind. Recently, the flow of information on stellar variability has increased strongly, requiring new approaches to GCVS compilation. New classification schemes are needed for variable stars, taking into account the development of our knowledge. We present information on the current state of the GCVS, its web data base, new Name-Lists containing thousands of new variables. We also discuss the problems of developing a new classification system for variable stars, of implementing catalogs of variable stars based on automatic surveys into the GCVS, of cooperation and interaction between the GCVS and other important sources of information on variable stars.

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36

Sinha, Tirthendu, Saurabh Sharma, A. K. Pandey, R. K. Yadav, K. Ogura, N. Matsunaga, N. Kobayashi, P. S. Bisht, R. Pandey, and A. Ghosh. "Variable stars in the Sh 2-170 H ii region." Monthly Notices of the Royal Astronomical Society 493, no. 1 (January 25, 2020): 267–87. http://dx.doi.org/10.1093/mnras/staa206.

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ABSTRACT We present multi-epoch deep (∼20 mag) Ic-band photometric monitoring of the Sh 2-170 star-forming region to understand the variability properties of pre-main-sequence (PMS) stars. We report identification of 47 periodic and 24 non-periodic variable stars with periods and amplitudes ranging from ∼4 h to 18 d and from ∼0.1 to 2.0 mag, respectively. We have further classified 49 variables as PMS stars (17 Class ii and 32 Class iii) and 17 as main-sequence (MS)/field star variables. A larger fraction of MS/field variables (88 per cent) show periodic variability as compared to the PMS variables (59 per cent). The ages and masses of the PMS variable stars are found to be comparable with those of T-Tauri stars. Their variability amplitudes show an increasing trend with the near-IR/mid-IR excess. The period distribution of the PMS variables shows two peaks, one near ∼1.5 d and the other near ∼4.5 d. It is found that the younger stars with thicker discs and envelopes seem to rotate slower than their older counterparts. These properties of the PMS variables support the disc-locking mechanism. Both the period and amplitude of PMS stars show decrease with increasing mass probably due to the effective dispersal of circumstellar discs in massive stars. Our results favour the notion that cool spots on weak line T-Tauri stars are responsible for most of their variations, while hot spots on classical T-Tauri stars resulting from variable mass accretion from an inner disc contribute to their larger amplitudes and irregular behaviours.

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37

Paunzen, E., M. Zejda, Z. Mikulášek, J. Liška, J. Krtička, J. Janík, M. Netopil, L. Fossati, and B. Baumann. "Variable stars in open clusters." Proceedings of the International Astronomical Union 9, S301 (August 2013): 471–72. http://dx.doi.org/10.1017/s174392131301510x.

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AbstractWe present our joint efforts to study variable stars in open clusters. This includes a new catalogue, a photometric survey for new variables, and the database WEBDA. Our tools will shed more light on stellar variability in open clusters.

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Sowicka, P., G. Handler, R. Taubner, M. Brunner, V. M. Passegger, F. Bauer, and E. Paunzen. "Variable stars in the field of the young open cluster Roslund 2." Proceedings of the International Astronomical Union 9, S301 (August 2013): 495–96. http://dx.doi.org/10.1017/s1743921313015226.

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AbstractThe study of variable stars in open clusters via asteroseismology is a powerful tool for the study of stellar evolution and stars in general. That is because stars in clusters can be assumed to originate from the same interstellar cloud, so they share similar properties such as age and overall metallicity. We performed a search for variable stars in the field of the young open star cluster Roslund 2, with photoelectric and CCD photometry acquired at two different telescopes. Within the resulting light curves we have found 12 variable stars. Our measurements confirm three previously known variables.

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Feast, Michael, and Patricia A. Whitelock. "Variable Stars and Galactic Structure." Proceedings of the International Astronomical Union 9, S298 (May 2013): 40–52. http://dx.doi.org/10.1017/s1743921313006182.

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AbstractVariable stars have a unique part to play in Galactic astronomy. Among the most important of these variables are the Cepheids (types I and II), the RR Lyraes and the Miras (O- and C-rich). The current status of the basic calibration of these stars in their roles as distance, structure and population indicators is outlined and some examples of recent applications of these stars to Galactic and extragalactic problems are reviewed. The expected impact of Gaia on this type of work is discussed and the need for complementary ground based observations, particularly large scale near-infrared photometry, is stressed.

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Rudnitskij, Georgij M. "Molecular Masers in Variable Stars." Publications of the Astronomical Society of Australia 19, no. 4 (2002): 499–504. http://dx.doi.org/10.1071/as02018.

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AbstractWhen a star with a mass of one to a few solar masses enters the red giant stage of its evolution, the radius of its atmosphere reaches several astronomical units. Pulsational instability is typical for this stage. Most stars become Mira-type or semiregular variables with light cycles of a few hundred days. Red giants lose mass at a rate M = 10−7−10−5M⊙ yr−1. Extensive gas–dust circumstellar envelopes form. These envelopes contain various molecular species. Some of these molecules (OH, H2O, SiO, HCN) manifest themselves in maser radio emission. Data on the H2O maser variability and its connection with the stellar brightness variations are discussed. In the H2O line circumstellar masers can be divided into ‘stable’ (showing persistent emission — R Aql, U Her, S CrB, X Hya) and ‘transient’ (appearing in the H2O line once per 10–15 stellar light cycles — R Leo, R Cas, U Aur). Physical mechanisms of the maser variability are discussed. The most probable process explaining the observed visual–H2O correlation is the influence of shock waves on the masing region. Usually it is assumed that shocks in Mira atmospheres are driven by stellar pulsations. Here an alternative explanation is proposed. If a star during its main sequence life possessed a planetary system, similar to the solar system, the planets will be embedded in a rather dense and hot medium. Effects of a planet revolving around a red giant at a short distance (inside its circumstellar envelope) are discussed. A shock produced by the supersonic motion of a planet can account for the correlated variability of the Hα line emission and H2O maser. If the planetary orbit is highly eccentric, then the connected Hα–H2O flare episodes may be explained by the periastron passage of the planet. New tasks for the upgraded ATCA are discussed.

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Ruban, E. V., G. A. Alekseeva, A. A. Arkharov, E. I. Hagen-Thorn, V. D. Galkin, I. N. Nikanorova, V. V. Novikov, V. P. Pakhomov, and T. Yu Puzakova. "Spectrophotometric observations of variable stars." Astronomy Letters 32, no. 9 (September 2006): 604–7. http://dx.doi.org/10.1134/s1063773706090052.

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Valenzuela, Lucas, and Karim Pichara. "Unsupervised classification of variable stars." Monthly Notices of the Royal Astronomical Society 474, no. 3 (November 13, 2017): 3259–72. http://dx.doi.org/10.1093/mnras/stx2913.

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Sánchez-Bajo, F., and J. M. Vaquero. "Variable stars in the classroom." European Journal of Physics 27, no. 3 (April 21, 2006): 635–46. http://dx.doi.org/10.1088/0143-0807/27/3/016.

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BUCHLER, J. ROBERT. "Chaotic Behavior in Variable Stars." Annals of the New York Academy of Sciences 497, no. 1 Chaotic Pheno (May 1987): 37–54. http://dx.doi.org/10.1111/j.1749-6632.1987.tb48709.x.

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Antonello, E., L. Fossati, D. Fugazza, L. Mantegazza, and W. Gieren. "Variable stars in nearby galaxies." Astronomy & Astrophysics 445, no. 3 (January 2006): 901–6. http://dx.doi.org/10.1051/0004-6361:20053822.

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Pichara, Karim, Pavlos Protopapas, and Daniel León. "META-CLASSIFICATION FOR VARIABLE STARS." Astrophysical Journal 819, no. 1 (February 24, 2016): 18. http://dx.doi.org/10.3847/0004-637x/819/1/18.

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Raga, A. C., J. Cantó, A. Esquivel, A. Rodríguez-González, and P. F. Velázquez. "Variable jets from young stars." Proceedings of the International Astronomical Union 5, H15 (November 2009): 256–57. http://dx.doi.org/10.1017/s1743921310009105.

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AbstractIn this paper we discuss the fact that the observed “accelerations” (i. e., higher velocities at larger distances from the source) observed along some Herbig-Haro (HH) jets directly imply that the ejection velocity has to be time-dependent. Even though discussed in the early literature of the subject, this is an often forgotten fact.

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Mantegazza, L., E. Antonello, D. Fugazza, M. Bossi, and S. Covino. "Variable stars in nearby galaxies." Astronomy & Astrophysics 367, no. 3 (March 2001): 759–69. http://dx.doi.org/10.1051/0004-6361:20000235.

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Antonello, E., D. Fugazza, L. Mantegazza, M. Stefanon, and S. Covino. "Variable stars in nearby galaxies." Astronomy & Astrophysics 386, no. 3 (May 2002): 860–64. http://dx.doi.org/10.1051/0004-6361:20020320.

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Antonello, E., D. Fugazza, and L. Mantegazza. "Variable stars in nearby galaxies." Astronomy & Astrophysics 388, no. 2 (May 31, 2002): 477–82. http://dx.doi.org/10.1051/0004-6361:20020553.

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