X-rays from M-type Giants—Signs of Late Stellar Activity?

Hünsch, M.; Konstantinova-Antova, R.; Schmitt, J. H. M. M.; Schröder, K.-P.; Kolev, D.; Medeiros, Jose-Renan de; Lèbre, A.; Udry, S.

doi:10.1017/s0074180900182142

Cited by 26 publications

(37 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The RV accuracy of NARVAL is 20−30 m s −1 (Moutou et al 2007;Aurière et al 2009 Hünsch et al (2004) and Famaey et al (2009) from measurements with CORAVEL (Udry et al 1997). Famaey et al (2009) included their EK Boo observations in two of their diagnosis plots and concluded that the star "appears amidst the non-binary M giants".…”

Section: Radial Velocity Binarity and Pulsationsmentioning

confidence: 93%

“…But in this case, v sin i has been determined. The CORAVEL value obtained on the basis of the cross-correllation method (Melo et al 2001) is 11 ± 1 km s −1 (Hünsch et al 2004). Our NARVAL data and the spectral synthesis method (permitting us to account for rotational and macroturbulent broadening) yield v sin i of 8.5 km s −1 with an accuracy 0.5 km s −1 .…”

Section: Rotationmentioning

confidence: 96%

“…The star attracted the attention of Hünsch et al (1998) because of its high X-ray luminosity. Later, Hünsch et al (2004) studied its variability in X-ray and optical activity indicators. They too ruled out the possibility of a symbiotic nature of EK Boo.…”

Section: Dynamo Operation and Its Originmentioning

confidence: 99%

“…A further study revealed its variability of L x , as well as its optical activity indicators Ca ii K&H and H α (Hunsch et al 2004). At the same time, EK Boo is considered to be a single star (Famaey et al 2009) with a projected rotation velocity of v sin i = 11 km s −1 (Hünsch et al 2004). A direct detection of its magnetic field was first reported by Konstantinova-Antova et al (2009).…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Direct detection of a magnetic field in the photosphere of the single M giant EK Bootis

Konstantinova-Antova

Aurière

Charbonnel

et al. 2010

A&A

View full text Add to dashboard Cite

Aims. We study the fast rotating M 5 giant EK Boo by means of spectropolarimetry to obtain direct and simultaneous measurements of both the magnetic field and activity indicators, in order to infer the origin of the activity in this fairly evolved giant. Methods. We used the new spectropolarimeter NARVAL at the Bernard Lyot Telescope (Observatoire du Pic du Midi, France) to obtain a series of Stokes I and Stokes V profiles for EK Boo. Using the least square deconvolution (LSD) technique we were able to detect the Zeeman signature of the magnetic field. We measured its longitudinal component by means of the averaged Stokes V and Stokes I profiles. The spectra also permitted us to monitor the Ca ii K&H chromospheric emission lines, which are well known as indicators of stellar magnetic activity. Results. From ten observations obtained between April 2008 and March 2009, we deduce that EK Boo has a magnetic field, which varied in the range of −0.1 to −8 G. On March 13, 2009, a complex structure of Stokes V was observed, which might indicate a dynamo. We also determined the initial mass and evolutionary stage of EK Boo, based on up-to-date stellar evolution tracks. The initial mass is in the range of 2.0−3.6 M , and EK Boo is either on the asymptotic giant branch (AGB), at the onset of the thermal pulse phase, or at the tip of the first (or red) giant branch (RGB). The fast rotation and activity of EK Boo might be explained by angular momentum dredge-up from the interior, or by the merging of a binary. In addition, we observed eight other M giants, which are known as X-ray emitters, or to be rotating fast for their class. For one of these, β And, presumably also an AGB star, we have a marginal detection of magnetic field, and a longitudinal component B l of about 1 G was measured. More observations like this will answer the question whether EK Boo is a special case, or whether magnetic activity is, rather, more common among M giants than expected.

show abstract

Section: Radial Velocity Binarity and Pulsationsmentioning

confidence: 93%

Section: Rotationmentioning

confidence: 96%

Section: Dynamo Operation and Its Originmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Direct detection of a magnetic field in the photosphere of the single M giant EK Bootis

Konstantinova-Antova

Aurière

Charbonnel

et al. 2010

A&A

View full text Add to dashboard Cite

show abstract

“…If this is the case for AGB stars, as proposed in the dynamic-magnetic models, then the X-ray luminosity should be a factor of $10 6 10 8 stronger than in the Sun (Soker & Zoabi 2002). Soker & Zoabi (2002) conclude that this expectation, of L X $ 10 31 10 35 ergs s À1 , is in sharp contradiction with most ROSAT observations; these observations demonstrate that the X-ray luminosities of red giant stars typically are only marginally larger than the solar X-ray luminosity (Schröder et al 1998) and that L X likely further decreases in late giant evolution (Hünsch & Schröder 1996). On the other hand, some red giants are known to be relatively luminous in X-rays (i.e., L X $ 10 30 ergs s À1 ; e.g., Hünsch & Schröder 1996;Hünsch 2001).…”

Section: Introductionmentioning

confidence: 94%

Constraining the X‐Ray Luminosities of Asymptotic Giant Branch Stars: TX Camelopardalis and T Cassiopeia

Kastner¹,

Soker²

2004

ApJ

View full text Add to dashboard Cite

To probe the magnetic activity levels of asymptotic giant branch (AGB) stars, we used XMM-Newton to search for X-ray emission from two well-studied objects, TX Cam and T Cas. The former star displays polarized maser emission, indicating magnetic field strengths of B $ 5 G, and the latter is one of the nearest known AGB stars. Neither star was detected by XMM-Newton. We use the upper limits on EPIC (CCD detector) count rates to constrain the X-ray luminosities of these stars and derive L X < 10 31 ergs s À1 (<10 30 ergs s À1 ) for an assumed X-ray emission temperature T X ¼ 3Â10 6 K (10 7 K). These limits represent P10% (P1%) of the X-ray luminosity expected under models in which AGB magnetic fields are global and potentially play an important role in collimating and/or launching AGB winds. We suggest, instead, that the B field strengths inferred from maser observations are representative of localized magnetic clouds.

show abstract