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

Ayres, Thomas R.

doi:10.1088/0004-637x/738/2/120

Cited by 10 publications

(11 citation statements)

References 39 publications

(45 reference statements)

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“…Open clusters have been a keystone in understanding stellar evolution because they contain stars at the same distance with similar reddening formed at the same time with the same chemical However, recently Ayres (2011) has suggested that there is evidence that the X-rays might actually be produced by a low-mass X-ray active companion.…”

Section: Introductionmentioning

confidence: 99%

XMM-NEWTONOBSERVATION OF THE α PERSEI CLUSTER

Pillitteri¹,

Evans²,

Wolk³

et al. 2013

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We report on the analysis of an archival observation of part of the α Persei cluster obtained with XMM-Newton. We detected 102 X-ray sources in the band 0.3-8.0 keV, of which 39 of them are associated with the cluster as evidenced by appropriate magnitudes and colors from 2MASS photometry. We extend the X-ray Luminosity Distribution (XLD) for M dwarfs, to add to the XLD found for hotter dwarfs from spatially extensive surveys of the whole cluster by ROSAT. Some of the hotter stars are identified as a background, possible slightly older group of stars at a distance of approximately 500 pc.1 1 Corresponding Author composition, at least to a first approximation. Their members display a range of masses, temperatures, luminosities, rotation rates, and multiplicity which can be explored. Comparison of cluster morphology provides an age sequence as a context for the evolution of stars. The well-known spindown of low mass stars with age due to magnetic braking provides a good example of insight from clusters. This slowing of rotation results in the decrease of coronal X-rays due to their connection with stellar dynamos. Good summaries of the decrease in stellar activity as stars age for a range of masses are provided by Favata and Micela (2003) and Güdel (2004).α Per is a young open cluster, found to be 50 Myr old from upper main sequence turnoff morphology (Meynet, Mermilliod, and Maeder, 1993). More recently, Stauffer, et al. (1999) have found an age of 90 Myr from the low mass lithium depletion boundary. Although there is some dispersion in the exact calibration of the age of the cluster, the sequence of age (increasing from the Orion Nebula Cluster through the α Per cluster through the Pleiades) is generally agreed. Thus, studies find a range in age from 50 to 90 Myr. We will use the shorthand "50 Myr" for the age of the cluster.This age makes it an excellent comparison for Cepheids and their companions. Indeed, α Per itself is a yellow supergiant, with similar parameters to Cepheids, except for its location at a temperature outside the instability strip. As an example of usage of the cluster, we have observed a number of Cepheids with the Hubble Space Telescope Wide Field Camera 3 to identify a population of resolved low-mass stars close to Cepheids which are probable physical companions. X-ray observations showing an activity level comparable to that of α Per dwarfs would confirm that they are young companions rather than chance alignments with old field stars (e.g. Evans, et al. 2012). Another interesting aspect of a cluster of this age is that it is the period when young planets have just finished forming, and thus we gain insight into the X-ray environment during the early formation of atmospheres.Because the cluster is nearby, it covers a wide area in the sky. It was observed with a raster of pointings by ROSAT . Essentially all the late F, G, and K members from the membership studies of Prosser (1992) were detected. Three deeper pointed ROSAT observations (22-25 ks) were subsequently made covering part of the ...

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Section: Introductionmentioning

confidence: 99%

XMM-NEWTONOBSERVATION OF THE α PERSEI CLUSTER

Pillitteri¹,

Evans²,

Wolk³

et al. 2013

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“…The iteration procedure used in Sect. 3.2 to estimate several fundamental parameters from model fitting to the SED indeed required E(B − V) = 0.0874 mag and R V = 3.1, a value that can imply a possible presence of "distant circumstellar shells from earlier epochs of mass loss", as noted by Ayres (2011).…”

Section: Sed Analysismentioning

confidence: 88%

“…Canopus presents high energy emission in the UV and X-ray, the physical origin of which is not completely understood: (i) a magnetic field of several hundred gauss, measured from Zeeman shifts on UV spectral lines, associated with periodic variations of a few days to a few weeks (e.g., Weiss 1986;Rakos et al 1977;Bychkov et al 2005Bychkov et al , 2009; (ii) far-UV emission lines showing non-symmetrical bisector curves with reverse C-shapes, revealing the present of opacity effects and/or velocity fields Dupree et al (2005); and (iii) a high X-ray luminosity L X of a few 10 30 erg s −1 (e.g., Vaiana et al 1981;Strassmeier et al 1998;Hunsch et al 1998;Testa et al 2004;Ayres 2011Ayres , 2017Ayres , 2018.…”

Section: Activity Temporal Variability and Spotsmentioning

confidence: 99%

Refined fundamental parameters of Canopus from combined near-IR interferometry and spectral energy distribution

Souza

Zorec

Millour

et al. 2021

A&A

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Context. Canopus, the brightest and closest yellow supergiant to our Solar System, offers a unique laboratory for understanding the physics of evolved massive stars. Aims. We aim at quantitatively exploring a large space of fundamental parameters of Canopus based on the combined analysis of its spectral energy distribution (SED) and optical-IR long baseline interferometry. Methods. We use the most recent high resolution near-IR data from the VLTI focal beam combiners PIONIER (H and K bands) and AMBER (K band), together with precise spectrophotometric measures that cover the SED of Canopus, from the UV to the IR, taken from ground and space observatories. Results. The accurate and precise PIONIER data allowed us to simultaneously measure the angular diameter and the limb darkening (LD) profile using different analytical laws. We found that the power-law LD, being also in agreement with predictions from stellar atmosphere models, reproduces the interferometric data well. For this model we measured an angular diameter of 7.184 ± 0.0017 ± 0.029 mas and an LD coefficient of 0.1438 ± 0.0015, which are respectively ≳5 and ~15−25 more precise than in our previous A&A paper on Canopus from 2008. From a dedicated analysis of the interferometric data, we also provide new constraints on the putative presence of weak surface inhomogeneities. Additionally, we analyzed the SED in a innovative way by simultaneously fitting the reddening-related parameters and the stellar effective temperature and gravity. We find that a model based on two effective temperatures is much better at reproducing the whole SED, from which we derived several parameters, including a new bolometric flux estimate: fbol = (59.22 ± 2.45) × 10−6 erg cm−2 s−1. We were also able to estimate the stellar mass from these measurements, and it is shown to be in agreement with additional predictions from evolutionary models, from which we inferred the age of Canopus as well. Conclusions. The Canopus angular diameter and LD measured in this work with PIONIER are the most precise to date, with a direct impact on several related fundamental parameters. Moreover, thanks to our joint analysis, we were able to determine a set of fundamental parameters that simultaneously reproduces both high-precision interferometric data and a good quality SED and, at the same time, agrees with stellar evolution models. This refined set of fundamental parameters constitutes a careful balance between the different methodologies used, providing invaluable observationally based constraints to models of stellar structure and evolution, which still present difficulties in simulating stars such as Canopus in detail.

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“…(The comparison stars will be utilized as a context in a series of "flux-flux" diagrams -pairing off combinations of coronal, subcoronal, and chromospheric diagnostics -introduced later.) -6 -The initial study (Ayres 2011) already presented a discussion of the stellar parameters of α Per and Canopus, but a few details can be updated. As reported then, α Per is a nonvariable supergiant, although close to the Instability Strip, with a (cluster) age of 50 Myr, mass of ∼ 7 M ⊙ , radius ∼ 63 R ⊙ , and effective temperature T eff ∼ 6270 K (about 500 K hotter than the Sun).…”

Section: Alpha Persei Canopus and Comparison Starsmentioning

confidence: 99%

“…The bright star was detected in X-rays as a hard coronal source (T ∼ 10 MK) in a 1993 pointing by ROSAT, at an X-ray luminosity (L X ) similar to other cluster members (all late-type dwarfs, except α Per itself: Prosser et al 1996). However, a subsequent far-ultraviolet (FUV) spectral SNAPshot 2 in 2010 by Hubble's Cosmic Origin Spectrograph (COS) uncovered what appeared to be a contradictory face of the supergiant (Ayres 2011). Expected strong coronal-proxy emission from Si IV 1393Å (T ∼ 8×10 4 K) was all but absent.…”

Section: Introductionmentioning

confidence: 99%

A Closer Look at the Alpha Persei Coronal Conundrum

Ayres

2017

ApJ

Self Cite

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A ROSAT survey of the Alpha Per open cluster in 1993 detected its brightest star, mid-F supergiant α Persei: the X-ray luminosity and spectral hardness were similar to coronally active late-type dwarf members. Later, in 2010, a Hubble Cosmic Origins Spectrograph SNAPshot of α Per found far-ultraviolet coronal proxy Si IV unexpectedly weak. This, and a suspicious offset of the ROSAT source, suggested that a late-type companion might be responsible for the X-rays. Recently, a multi-faceted program tested that premise. Groundbased optical coronography, and near-UV imaging with HST Wide Field Camera 3, searched for any close-in faint candidate coronal objects, but without success. Then, a Chandra pointing found the X-ray source single and coincident with the bright star. Significantly, the Si IV emissions of α Per, in a deeper FUV spectrum collected by HST COS as part of the joint program, aligned well with chromospheric atomic oxygen (which must be intrinsic to the luminous star), within the context of cooler late-F and early-G supergiants, including Cepheid variables. This pointed to the X-rays as the fundamental anomaly. The overluminous X-rays still support the case for a hyperactive dwarf secondary, albeit now spatially unresolved. However, an alternative is that α Per represents a novel class of coronal source. Resolving the first possibility now has become more difficult, because the easy solution -a well separated companion -has been eliminated. Testing the other possibility will require a broader high-energy census of the early-F supergiants.Subject headings: ultraviolet: stars -stars: individual (HD 20902= α Per; HD 45348= α Car) -stars: coronae Ignoring these caveats for the moment, the suspicious ROSAT offset, bolstered by the 1 In what follows, "α Per" normally will refer to the star, while "Alpha Per" normally will denote the cluster. In cases where "Alpha Persei" appears, the specific usage is guided by the context.2 Brief, partial-orbit observations to fill gaps in the HST schedule.3 Position Sensitive Proportional Counter, the main X-ray imager of ROSAT.

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

Cited by 10 publications

References 39 publications

XMM-NEWTONOBSERVATION OF THE α PERSEI CLUSTER

XMM-NEWTONOBSERVATION OF THE α PERSEI CLUSTER

Refined fundamental parameters of Canopus from combined near-IR interferometry and spectral energy distribution

A Closer Look at the Alpha Persei Coronal Conundrum

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