<i>CHANDRA</i>OBSERVATION OF POLARIS: CENSUS OF LOW-MASS COMPANIONS

Evans, Nancy Remage; Guinan, E. F.; Engle, Scott G.; Wolk, S. J.; Schlegel, Eric M.; Mason, Brian D.; Karovska, M.; Spitzbart, B.

doi:10.1088/0004-6256/139/5/1968

Cited by 18 publications

(17 citation statements)

References 28 publications

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“…Searching for x-ray emission from lower-mass stars near ζ Gem is likewise a viable pursuit for corroborating membership (Evans 2011;Evans et al 2011). However, the star Polaris B is of a similar spectral type as ζ Gem B (Turner 1977), and does not exhibit x-ray emission (Evans et al 2010).…”

Section: Conclusion and Future Researchmentioning

confidence: 99%

Discovery of the Host Cluster for the Fundamental Cepheid Calibrator Zeta Geminorum

Majaess

Turner

Gieren

et al. 2012

ApJ

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New and existing CORAVEL, U BV JHK s , HST, HIP/Tycho, ARO, KPNO, and DAO observations imply that the fundamental Cepheid calibrator ζ Gem is a cluster member. The following parameters were inferred for ζ Gem from cluster membership and are tied to new spectral classifications (DAO) established for 26 nearby stars (e.g., HD53588/B7.5IV, HD54692/B9.5IV): E B−V = 0.02 ± 0.02, log τ = 7.85 ± 0.15, and d = 355 ± 15 pc. The mean distance to ζ Gem from cluster membership and six recent estimates (e.g., IRSB) is d = 363 ± 9(σx) ± 26(σ) pc. The results presented here support the color-excess and HST parallax derived for the Cepheid by Benedict et al. (2007). Forthcoming precise proper motions (DASCH) and Chandra/XMM-Newton observations of the broader field may be employed to identify cluster members, bolster the cluster's existence, and provide stronger constraints on the Cepheid's fundamental parameters.

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Section: Conclusion and Future Researchmentioning

confidence: 99%

Discovery of the Host Cluster for the Fundamental Cepheid Calibrator Zeta Geminorum

Majaess

Turner

Gieren

et al. 2012

ApJ

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“…A database of the known binary and multiple Galactic CCs is maintained at Konkoly Observatory 3 (Szabados 2003b). Low-mass companions with surface magnetic fields generated by convection have been detected using their X-ray emission (Evans et al 2010), including for Cepheids in clusters (Evans et al 2014). Binary Cepheids have also been identified in the Magellanic Clouds (Szabados & Nehéz 2012) in particular in eclipsing binary systems (Alcock et al 2002;Lepischak et al 2004;Pietrzyński et al 2010;Pilecki et al 2013Pilecki et al , 2015Gieren et al 2015) that provide extremely accurate stellar parameters (Pilecki et al 2018).…”

Section: Introductionmentioning

confidence: 99%

Multiplicity of Galactic Cepheids and RR Lyrae stars from Gaia DR2

Kervella

Gallenne

Evans

et al. 2019

A&A

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Context. Classical Cepheids (CCs) and RR Lyrae stars (RRLs) are important classes of variable stars used as standard candles to estimate galactic and extragalactic distances. Their multiplicity is imperfectly known, particularly for RRLs. Astoundingly, to date only one RRL has convincingly been demonstrated to be a binary, TU UMa, out of tens of thousands of known RRLs. Aims. Our aim is to detect the binary and multiple stars present in a sample of Milky Way CCs and RRLs. Methods. In the present article, we combine the HIPPARCOS and Gaia DR2 positions to determine the mean proper motion of the targets, and we search for proper motion anomalies (PMa) caused by close-in orbiting companions. Results. We identify 57 CC binaries from PMa out of 254 tested stars and 75 additional candidates, confirming the high binary fraction of these massive stars. For 28 binary CCs, we determine the companion mass by combining their spectroscopic orbital parameters and astrometric PMa. We detect 13 RRLs showing a significant PMa out of 198 tested stars, and 61 additional candidates. Conclusions. We determine that the binary fraction of CCs is likely above 80%, while that of RRLs is at least 7%. The newly detected systems will be useful to improve our understanding of their evolutionary states. The discovery of a significant number of RRLs in binary systems also resolves the long-standing mystery of their extremely low apparent binary fraction.

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“…It would be tempting to continue in this vein and begin attributing anomalous coronal sources among the somewhat cooler (than α Per and α Car), but still luminous Cepheids (e.g., Evans et al 2010), to low-mass companions. But there is an important caveat.…”

Section: Discussionmentioning

confidence: 99%

The Curious Case of the Alpha Persei Corona: A Dwarf in Supergiant's Clothing?

Ayres

2011

ApJ

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Alpha Persei (HD 20902: F5 Iab) is a luminous, nonvariable supergiant located at the blue edge of the Cepheid instability strip. It is one of the brightest coronal X-ray sources in the young open cluster bearing its name, yet warm supergiants as a class generally avoid conspicuous high-energy activity. The Cosmic Origins Spectrograph on the Hubble Space Telescope has recently uncovered additional oddities. The 1290-1430 Å far-ultraviolet (FUV) spectrum of α Per is dominated by photospheric continuum emission, with numerous superposed absorption features, mainly stellar. However, the normal proxies of coronal activity, such as the Si iv 1400 Å doublet (T ∼ 8 × 10 4 K), are very weak, as are the chromospheric C ii 1335 Å multiplet (T ∼ 3 × 10 4 K) and O i 1305 Å triplet. In fact, the Si iv features of α Per are not only narrower than those of later, G-type supergiants of similar L X /L bol , but are also fainter (in L Si iv /L bol ) by two orders of magnitude. Further, a reanalysis of the ROSAT pointing on α Per finds the X-ray centroid offset from the stellar position by 9 , at a moderate level of significance. The FUV and X-ray discrepancies raise the possibility that the coronal source might be unrelated to the supergiant, perhaps an accidentally close dwarf cluster member; heretofore unrecognized in the optical, lost in the glare of the bright star.

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CHANDRAOBSERVATION OF POLARIS: CENSUS OF LOW-MASS COMPANIONS

Cited by 18 publications

References 28 publications

Discovery of the Host Cluster for the Fundamental Cepheid Calibrator Zeta Geminorum

Discovery of the Host Cluster for the Fundamental Cepheid Calibrator Zeta Geminorum

Multiplicity of Galactic Cepheids and RR Lyrae stars from Gaia DR2

The Curious Case of the Alpha Persei Corona: A Dwarf in Supergiant's Clothing?

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