Going Forward to Unveil the Nature of γ Cas Analogs

[en] The star γ Cas and its analogs are a subset of Be stars that display particularly hard and bright thermal X-ray emission, which has no equivalent among other massive stars. Here, I will review their characteristics and present the latest results of our optical and X-ray monitoring campaigns, including an assessment of the links between the circumstellar environment and the high-energy properties. Possible scenarios to explain this phenomenon will be presented in light of these observational results.

Research Center/Unit :

STAR - Space sciences, Technologies and Astrophysics Research - ULiège

Disciplines :

Space science, astronomy & astrophysics

Author, co-author :

Nazé, Yaël ; Université de Liège - ULiège > Département d'astrophysique, géophysique et océanographie (AGO) > Groupe d'astrophysique des hautes énergies (GAPHE)

Language :

English

Title :

Going Forward to Unveil the Nature of γ Cas Analogs

Publication date :

24 January 2025

Journal title :

Galaxies

eISSN :

2075-4434

Publisher :

MDPI

Volume :

Issue :

Pages :

id 8 (7p)

Peer reviewed :

Peer Reviewed verified by ORBi

Additional URL :

https://www.mdpi.com/2075-4434/13/1/8/pdf

Funders :

F.R.S.-FNRS - Fonds de la Recherche Scientifique
ESA - European Space Agency
BELSPO - Belgian Federal Science Policy Office

Available on ORBi :

since 27 January 2025

Statistics

Number of views

67 (1 by ULiège)

Number of downloads

46 (0 by ULiège)

More statistics

Scopus citations^®

Scopus citations^®
without self-citations

OpenCitations

OpenAlex citations

Bibliography

Feldmeier A. Puls J. Pauldrach A.W.A. A possible origin for X-rays from O stars Astron. Astrophys. 1997 322 878 895
Berghoefer T.W. Schmitt J.H.M.M. Danner R. Cassinelli J.P. X-ray properties of bright OB-type stars detected in the ROSAT all-sky survey Astron. Astrophys. 1997 322 167 174
Oskinova L.M. Evolution of X-ray emission from young massive star clusters Mon. Not. R. Astron. Soc. 2005 361 679 694 10.1111/j.1365-2966.2005.09229.x
Waldron W.L. Cassinelli J.P. An Extensive Collection of Stellar Wind X-Ray Source Region Emission Line Parameters, Temperatures, Velocities, and Their Radial Distributions as Obtained from Chandra Observations of 17 OB Stars Astrophys. J. 2007 668 456 480 10.1086/520919
Zhekov S.A. Palla F. X-rays from massive OB stars: Thermal emission from radiative shocks Mon. Not. R. Astron. Soc. 2007 382 1124 1132 10.1111/j.1365-2966.2007.12286.x
Nazé Y. Hot stars observed by XMM-Newton. I. The catalog and the properties of OB stars Astron. Astrophys. 2009 506 1055 1064 10.1051/0004-6361/200912659
Nazé Y. Broos P.S. Oskinova L. Townsley L.K. Cohen D. Corcoran M.F. Evans N.R. Gagné M. Moffat A.F.J. Pittard J.M. et al. Global X-ray Properties of the O and B Stars in Carina Astrophys. J. Suppl. 2011 194 7 10.1088/0067-0049/194/1/7
Nazé Y. Oskinova L.M. Gosset E. A Detailed X-Ray Investigation of ζ Puppis. II. The Variability on Short and Long Timescales Astrophys. J. 2013 763 143 10.1088/0004-637X/763/2/143
Huenemoerder D.P. Ignace R. Miller N.A. Gayley K.G. Hamann W.R. Lauer J. Moffat A.F.J. Nazé Y. Nichols J.S. Oskinova L. et al. A Deep Exposure in High Resolution X-Rays Reveals the Hottest Plasma in the ζ Puppis Wind Astrophys. J. 2020 893 52 10.3847/1538-4357/ab8005
Cohen D.H. Parts W. Doskoch G.M. Wang J. Petit V. Leutenegger M.A. Gagné M. Chandra grating spectroscopy of embedded wind shock X-ray emission from O stars shows low plasma temperatures and significant wind absorption Mon. Not. R. Astron. Soc. 2021 503 715 725 10.1093/mnras/stab270
Gunderson S.J. Gayley K.G. Huenemoerder D.P. Support for the standard picture of thermal X-rays in the wind of ζ Puppis from dielectronic recombination of He-like ions Mon. Not. R. Astron. Soc. 2023 522 2739 2746 10.1093/mnras/stad1163
Oskinova L.M. Nazé Y. Todt H. Huenemoerder D.P. Ignace R. Hubrig S. Hamann W.R. Discovery of X-ray pulsations from a massive star Nat. Commun. 2014 5 4024 10.1038/ncomms5024
Nichols J.S. Nazé Y. Huenemoerder D.P. Moffat A.F.J. Miller N.A. Lauer J. Ignace R. Gayley K. Ramiaramanantsoa T. Oskinova L. et al. Correlated X-Ray and Optical Variability in the O-Type Supergiant ζ Puppis Astrophys. J. 2021 906 89 10.3847/1538-4357/abca3a
ud-Doula A. Nazé Y. Magnetically confined wind shocks in X-rays—A review Adv. Space Res. 2016 58 680 693 10.1016/j.asr.2015.09.025
Rauw G. Nazé Y. X-ray and optical spectroscopy of the massive young open cluster IC 1805 Astron. Astrophys. 2016 594 A82 10.1051/0004-6361/201629207
Smith M.A. Lopes de Oliveira R. Motch C. The X-ray emission of the γ Cassiopeiae stars Adv. Space Res. 2016 58 782 808 10.1016/j.asr.2015.12.032
Smith M.A. Cohen D.H. Gu M.F. Robinson R.D. Evans N.R. Schran P.G. High-Resolution Chandra Spectroscopy of γ Cassiopeiae (B0.5e) Astrophys. J. 2004 600 972 985 10.1086/379873
Shrader C.R. Hamaguchi K. Sturner S.J. Oskinova L.M. Almeyda T. Petre R. High-energy Properties of the Enigmatic Be Star γ Cassiopeiae Astrophys. J. 2015 799 84 10.1088/0004-637X/799/1/84
Tsujimoto M. Morihana K. Hayashi T. Kitaguchi T. Suzaku and NuSTAR X-Ray Spectroscopy of γ Cassiopeiae and HD 110432 Publ. Astron. Soc. Jpn. 2018 70 109 10.1093/pasj/psy111
Smith M.A. Robinson R.D. Corbet R.H.D. A Multiwavelength Campaign on γ Cassiopeiae. I. The Case for Surface X-Ray Flaring Astrophys. J. 1998 503 877 893 10.1086/306006
Robinson R.D. Smith M.A. A Search for Rotational Modulation of X-Ray Centers on the Classical Be Star γ Cassiopeiae Astrophys. J. 2000 540 474 488 10.1086/309310
Robinson R.D. Smith M.A. Henry G.W. X-Ray and Optical Variations in the Classical Be Star γ Cassiopeia: The Discovery of a Possible Magnetic Dynamo Astrophys. J. 2002 575 435 448 10.1086/341141
Hamaguchi K. Oskinova L. Russell C.M.P. Petre R. Enoto T. Morihana K. Ishida M. Discovery of Rapidly Moving Partial X-ray Absorbers within Gamma Cassiopeiae Astrophys. J. 2016 832 140 10.3847/0004-637X/832/2/140
Rauw G. Nazé Y. Motch C. Smith M.A. Guarro Fló J. Lopes de Oliveira R. The X-Ray Emission of γ Cassiopeiae During the 2020–2021 Disc Eruption Astron. Astrophys. 2022 664 A184 10.1051/0004-6361/202243679
Nebot Gómez-Morán A. Motch C. Barcons X. Carrera F.J. Ceballos M.T. Cropper M. Grosso N. Guillout P. Hérent O. Mateos S. et al. The XMM-Newton SSC survey of the Galactic plane Astron. Astrophys. 2013 553 A12 10.1051/0004-6361/201220308
Nazé Y. Motch C. Hot stars observed by XMM-Newton. II. A survey of Oe and Be stars Astron. Astrophys. 2018 619 A148 10.1051/0004-6361/201833842
Nazé Y. Motch C. Rauw G. Kumar S. Robrade J. Lopes de Oliveira R. Smith M.A. Torrejón J.M. Three discoveries of γ Cas analogues from dedicated XMM-Newton observations of Be stars Mon. Not. R. Astron. Soc. 2020 493 2511 2517 10.1093/mnras/staa457
Nazé Y. Robrade J. SRG/eROSITA survey of Be stars Mon. Not. R. Astron. Soc. 2023 525 4186 4201 10.1093/mnras/stad2399
Nazé Y. Rauw G. Pigulski A. TESS light curves of γ Cas stars Mon. Not. R. Astron. Soc. 2020 498 3171 3183 10.1093/mnras/staa2553
Reig P. Be/X-ray binaries Astrophys. Space Sci. 2011 332 1 29 10.1007/s10509-010-0575-8
Kennea J.A. Coe M.J. Evans P.A. Townsend L.J. Campbell Z.A. Udalski A. Swift J011511.0-725611: Discovery of a rare Be star/white dwarf binary system in the SMC Mon. Not. R. Astron. Soc. 2021 508 781 788 10.1093/mnras/stab2632
Wang L. Gies D.R. Peters G.J. Götberg Y. Chojnowski S.D. Lester K.V. Howell S.B. The Detection and Characterization of Be+sdO Binaries from HST/STIS FUV Spectroscopy Astron. J. 2021 161 248 10.3847/1538-3881/abf144
Nazé Y. Rauw G. Czesla S. Smith M.A. Robrade J. Velocity monitoring of γ Cas stars reveals their binarity status Mon. Not. R. Astron. Soc. 2022 510 2286 2304 10.1093/mnras/stab3378
Gies D.R. Wang L. Klement R. Gamma Cas Stars as Be+White Dwarf Binary Systems Astrophys. J. Lett. 2023 942 L6 10.3847/2041-8213/acaaa1
Langer N. Baade D. Bodensteiner J. Greiner J. Rivinius T. Martayan C. Borre C.C. γ Cas stars: Normal Be stars with discs impacted by the wind of a helium-star companion? Astron. Astrophys. 2020 633 A40 10.1051/0004-6361/201936736
Nazé Y. Rauw G. Smith M.A. Motch C. The X-ray emission of Be+stripped star binaries Mon. Not. R. Astron. Soc. 2022 516 3366 3380 10.1093/mnras/stac2245
Postnov K. Oskinova L. Torrejón J.M. A propelling neutron star in the enigmatic Be-star γ Cassiopeia Mon. Not. R. Astron. Soc. 2017 465 L119 L123 10.1093/mnrasl/slw223
Smith M.A. Lopes de Oliveira R. Motch C. Is there a propeller neutron star in γ Cas? Mon. Not. R. Astron. Soc. 2017 469 1502 1509 10.1093/mnras/stx926
Rauw G. Fluorescent Fe K line emission of γ Cas stars. I. Do γ Cas stars host propelling neutron stars? Astron. Astrophys. 2024 682 A179 10.1051/0004-6361/202348076
Slettebak A. Snow T.P. J. Spectrophotometric variability in the Be star gamma Cassiopeiae: Simultaneous ultraviolet and Halpha observations Astrophys. J. Lett. 1978 224 L127 L131 10.1086/182775
Peters G. The hard X-ray flux from GAM CAS during 1970–73 Publ. Astron. Soc. Pac. 1982 94 157 161 10.1086/130955
Murakami T. Koyama K. Inoue H. Agrawal P.C. X-Ray Spectrum from Gamma Cassiopeiae Astrophys. J. Lett. 1986 310 L31 10.1086/184776
Smith M.A. Dynamic Processes in Be Star Atmospheres. III. Rapid Multiwavelength Variability in gamma Cassiopeiae Astrophys. J. 1995 442 812 10.1086/175485
Smith M.A. Ultraviolet Activity as Indicators of Small-scale Magnetic Fields in γ Cassiopeiae Publ. Astron. Soc. Pac. 2019 131 044201 10.1088/1538-3873/aaf70b
Smith M.A. Robinson R.D. Hatzes A.P. A Multiwavelength Campaign on γ Cassiopeiae. II. The Case for Corotating, Circumstellar Clouds Astrophys. J. 1998 507 945 954 10.1086/306347
Motch C. Lopes de Oliveira R. Smith M.A. The Origin of the Puzzling Hard-X-Ray Emission of γ Cassiopeiae Astrophys. J. 2015 806 177 10.1088/0004-637X/806/2/177
Rauw G. Nazé Y. Smith M.A. Miroshnichenko A.S. Guarro Fló J. Campos F. Prendergast P. Danford S. González-Pérez J.N. Hempelmann A. et al. Intriguing X-ray and optical variations of the γ Cassiopeiae analog HD 45314 Astron. Astrophys. 2018 615 A44 10.1051/0004-6361/201731782
Nazé Y. Motch C. Rauw G. Smith M.A. Robrade J. X-raying the ζ Tau binary system Astron. Astrophys. 2024 688 A181 10.1051/0004-6361/202449737
Nazé Y. Rauw G. Bohlsen T. Heathcote B. Mc Gee P. Cacella P. Motch C. X-ray response to disc evolution in two γ Cas stars Mon. Not. R. Astron. Soc. 2022 512 1648 1657 10.1093/mnras/stac314
Nazé Y. Rauw G. Smith M. Surprises in the simultaneous X-ray and optical monitoring of π Aquarii Astron. Astrophys. 2019 632 A23 10.1051/0004-6361/201936307