Fundamental parameters and infrared excesses of<i>Hipparcos</i>stars

McDonald, Iain; Zijlstra, A. A.; Boyer, Martha L.

doi:10.1111/j.1365-2966.2012.21873.x

Cited by 244 publications

(277 citation statements)

References 58 publications

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“…van Leeuwen (2007) reported a Hipparcos parallax of 20.31 mas, placing it at a distance of r ≈ 49 pc. McDonald et al (2012) reported an effective temperature of T eff ≈ 6032 K, while the estimate of Vican & Schneider (2014) was T eff ≈ 6100 K. Furthermore, Vican & Schneider (2014) reported a radius of R ≈ 1.05 R , while Zuckerman et al (2011) presented the value R ≈ 1.08 R . We adopted the value 1.1 R .…”

Section: V1358 Orimentioning

confidence: 99%

Zeeman-Doppler imaging of active young solar-type stars

Hackman

Lehtinen

Rosén

et al. 2016

A&A

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Context. By studying young magnetically active late-type stars, i.e. analogues to the young Sun, we can draw conclusions on the evolution of the solar dynamo. Aims. We determine the topology of the surface magnetic field and study the relation between the magnetic field and cool photospheric spots in three young late-type stars. Methods. High-resolution spectropolarimetry of the targets was obtained with the HARPSpol instrument mounted at the ESO 3.6 m telescope. The signal-to-noise ratios of the Stokes IV measurements were boosted by combining the signal from a large number of spectroscopic absorption lines through the least squares deconvolution technique. Surface brightness and magnetic field maps were calculated using the Zeeman-Doppler imaging technique.Results. All three targets show clear signs of magnetic fields and cool spots. Only one of the targets, V1358 Ori, shows evidence of the dominance of non-axisymmetric modes. In two of the targets, the poloidal field is significantly stronger than the toroidal one, indicative of an α 2 -type dynamo, in which convective turbulence effects dominate over the weak differential rotation. In two of the cases there is a slight anti-correlation between the cool spots and the strength of the radial magnetic field. However, even in these cases the correlation is much weaker than in the case of sunspots. Conclusions. The weak correlation between the measured radial magnetic field and cool spots may indicate a more complex magnetic field structure in the spots or spot groups involving mixed magnetic polarities. Comparison with a previously published magnetic field map shows that on one of the stars, HD 29615, the underlying magnetic field changed its polarity between 2009 and 2013.

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Section: V1358 Orimentioning

confidence: 99%

Zeeman-Doppler imaging of active young solar-type stars

Hackman

Lehtinen

Rosén

et al. 2016

A&A

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“…Silicates are also expected to produce spectral features in the 8-14 µm range, unless the grains are extremely large. Amorphous carbon, on the other hand, can produce a featureless mid-infrared continuum (McDonald et al 2012). Amorphous carbon has also been favored in the cases of other dust producing WRs (Williams et al 1987), and so it might be the most plausible dust chemistry for NaSt1.…”

Section: Dust Formation From Colliding Winds?mentioning

confidence: 99%

Multiwavelength observations of NaSt1 (WR 122): equatorial mass loss and X-rays from an interacting Wolf–Rayet binary

Mauerhan

Smith

Dyk

et al. 2015

Monthly Notices of the Royal Astronomical Society

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NaSt1 (aka Wolf-Rayet 122) is a peculiar emission-line star embedded in an extended nebula of [N ii] emission with a compact dusty core. This object was characterized by Crowther & Smith (1999) as a Wolf-Rayet (WR) star cloaked in an opaque nebula of CNO-processed material, perhaps analogous to η Car and its Homunculus nebula, albeit with a hotter central source. To discern the morphology of the [N ii] nebula we performed narrowband imaging using the Hubble Space Telescope and Wide-field Camera 3. The images reveal that the nebula has a disk-like geometry tilted ≈12 • from edge-on, composed of a bright central ellipsoid surrounded by a larger clumpy ring. Ground-based spectroscopy reveals radial velocity structure (±10 km s −1 ) near the outer portions of the nebula's major axis, which is likely to be the imprint of outflowing gas. Near-infrared adaptive-optics imaging with Magellan AO has resolved a compact ellipsoid of K s -band emission aligned with the larger [N ii] nebula, which we suspect is the result of scattered He i line emission (λ2.06 µm). Observations with the Chandra X-ray Observatory have revealed an X-ray point source at the core of the nebula that is heavily absorbed at energies < 1 keV and has properties consistent with WR stars and colliding-wind binaries. We suggest that NaSt1 is a WR binary embedded in an equatorial outflow that formed as the result of non-conservative mass transfer. NaSt1 thus appears to be a rare and important example of a stripped-envelope WR forming through binary interaction, caught in the brief Roche-lobe overflow phase.

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“…We first approximate the spectrum of the PSF reference star with a template spectrum with the corresponding effective temperature and the luminosity class available in the spectral library of Pickles (1998). Based on the effective temperature of 4548 K estimated for HIP67834 (McDonald et al 2012), we adopted the spectrum of a K2III star in the spectral library of Pickles (1998), whose effective temperature is the closest to HIP67834. We reddended the spectrum with A V = 0.24, which was obtained using the parameterization of the interstellar extinction of Arenou et al (1992) and the wavelength-dependence of the interstellar extinction derived by Cardelli et al (1989).…”

Section: Visible Polarimetric Imaging Observations With Sphere-zimpolmentioning

confidence: 99%

Clumpy dust clouds and extended atmosphere of the AGB star W Hydrae revealed with VLT/SPHERE-ZIMPOL and VLTI/AMBER

Ohnaka

Weigelt

Hofmann

2016

A&A

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Aims. Our recent visible polarimetric images of the well-studied AGB star W Hya taken at pre-maximum light (phase 0.92) with VLT/SPHERE-ZIMPOL have revealed clumpy dust clouds close to the star at ∼2 R . We present second-epoch SPHERE-ZIMPOL observations of W Hya at minimum light (phase 0.54) as well as high-spectral resolution long-baseline interferometric observations with the AMBER instrument at the Very Large Telescope Interferometer (VLTI). Methods. We observed W Hya with VLT/SPHERE-ZIMPOL at three wavelengths in the continuum (645, 748, and 820 nm), in the Hα line at 656.3 nm, and in the TiO band at 717 nm. The VLTI/AMBER observations were carried out in the wavelength region of the CO first overtone lines near 2.3 µm with a spectral resolution of 12 000. Results. The high-spatial resolution polarimetric images obtained with SPHERE-ZIMPOL have allowed us to detect clear time variations in the clumpy dust clouds as close as 34-50 mas (1.4-2.0 R ) to the star. We detected the formation of a new dust cloud as well as the disappearance of one of the dust clouds detected at the first epoch. The Hα and TiO emission extends to ∼150 mas (∼6 R ), and the Hα images obtained at two epochs reveal time variations. The degree of linear polarization measured at minimum light, which ranges from 13 to 18%, is higher than that observed at pre-maximum light. The power-law-type limb-darkened disk fit to the AMBER data in the continuum results in a limb-darkened disk diameter of 49.1 ± 1.5 mas and a limb-darkening parameter of 1.16±0.49, indicating that the atmosphere is more extended with weaker limb-darkening compared to pre-maximum light. Our Monte Carlo radiative transfer modeling shows that the second-epoch SPHERE-ZIMPOL data can be explained by a shell of 0.1 µm grains of Al 2 O 3 , Mg 2 SiO 4 , and MgSiO 3 with a 550 nm optical depth of 0.6±0.2 and an inner and outer radii of 1.3 R and 10±2 R , respectively. Our modeling suggests the predominance of small (0.1 µm) grains at minimum light, in marked contrast to the predominance of large (0.5 µm) grains at pre-maximum light. Conclusions. The variability phase dependence of the characteristic grain size implies that small grains might just have started to form at minimum light in the wake of a shock, while the pre-maximum light phase might have corresponded to the phase of efficient grain growth.

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Fundamental parameters and infrared excesses ofHipparcosstars

Cited by 244 publications

References 58 publications

Zeeman-Doppler imaging of active young solar-type stars

Zeeman-Doppler imaging of active young solar-type stars

Multiwavelength observations of NaSt1 (WR 122): equatorial mass loss and X-rays from an interacting Wolf–Rayet binary

Clumpy dust clouds and extended atmosphere of the AGB star W Hydrae revealed with VLT/SPHERE-ZIMPOL and VLTI/AMBER

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