MG Emission from Hybrid-Chromosphere Stars: 1.5 Decades of Chromospheric Variability Monitoring

Brown, Alexander; Deeney, B. D.; Ayres, Thomas R.; Veale, Anthony; Bennett, P. D.

doi:10.1086/192365

Cited by 15 publications

(10 citation statements)

References 17 publications

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“…stellar chromospheric studies. Typical spectroscopic diagnostic lines include Ca ii H and K, Mg ii h and k, and Ly (Brown et al 1996;Schrijver & Zwaan 2000), which our data unfortunately do not include. G227-5's spectrum ( Fig.…”

Section: Chromospheric Structurementioning

confidence: 91%

The Discovery of Oxygen‐rich Chromospheres in Two Massive DQ White Dwarfs

Provençal

Shipman

MacDonald

2005

ApJ

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We present HST observations of the massive DQ white dwarfs G227-5 and G35-26 in which we find the first clear evidence of chromospheric activity in cool field white dwarfs. The chromospheric spectra, obtained over a very narrow wavelength range, show lines of the usually expected species O i, N i, C ii, and possibly Si iii and Mg ii. The O i/C ii line strengths are considerably higher than usually found in main-sequence chromospheres. However, the hypothesis that these high line strengths represent a genuine oxygen overabundance in these stars is less likely than the interpretation that the oxygen abundance is enhanced by one or more of the well-known effects that can alter chromospheric abundances.

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Section: Chromospheric Structurementioning

confidence: 91%

The Discovery of Oxygen‐rich Chromospheres in Two Massive DQ White Dwarfs

Provençal

Shipman

MacDonald

2005

ApJ

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“…Following the method given by Brown et al (1996), synthetic time series data was generated with the same sampling as the observed data and the frequencies were searched over the same range as done with the real data. The synthetic time series are built by using a random number generator with a Gaussian distribution of points…”

Section: Methods Bmentioning

confidence: 99%

“…Following the method given by Brown et al (1996), synthetic time‐series data were generated with the same sampling as the observed data and the frequencies were searched over the same range as done with the real data. The synthetic time series is built by using a random number generator with a Gaussian distribution of points where x represents the magnitude of the light curve, α= exp(−Δ t / L corr ), where Δ t is the time between magnitudes x i −1 and x i , β= (1 −α 2 ) 1/2 , and R (0, σ) is the random number generator with a dispersion σ, which is the variance of the time‐series data.…”

Section: Data Reductionmentioning

confidence: 99%

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Exploring pre-main-sequence variables of the ONC: the new variables

Parihar

Messina

Distefano

et al. 2009

Monthly Notices of the Royal Astronomical Society

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Since 2004, we have been engaged in a long-term observing programme to monitor young stellar objects (YSOs) in the Orion Nebula Cluster (ONC). We have collected about 2000 frames in V, R and I broad-band filters on more than 200 nights distributed over five consecutive observing seasons. The high-quality and time-extended photometric data give us an opportunity to address various phenomena associated with young stars. The prime motivations of this project are (i) to explore various manifestations of stellar magnetic activity in very young low-mass stars, (ii) to search for new pre-main-sequence eclipsing binaries and (iii) to look for any EXor and FUor-like transient activities associated with YSOs. Since this is the first paper on this programme, we give a detailed description of the science drivers, the observation and the data reduction strategies as well. In addition to these, we also present a large number of new periodic variables detected from our first 5 yr of time-series photometric data. Our study reveals that about 72 per cent of classical T Tauri stars (CTTS) in our field of view are periodic, whereas only 32 per cent of weak-lined T Tauri stars (WTTS) are periodic. This indicates that inhomogeneity patterns on the surface of CTTS of the ONC stars are much more stable than on WTTS. From our multiyear monitoring campaign, we found that the photometric surveys based on single season are incapable of identifying all periodic variables. And any study on evolution of angular momentum based on single-season surveys must be carried out with caution.

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“…Some hybrid bright giants of slightly earlier spectral type show evidence of terminal velocities comparable to the escape speed V 1 =V esc $ 1. For example, Aqr (G2 Ib; Dupree et al 1992b) and TrA ( K3 II) have been observed infrequently to show such a high-velocity wind component in addition to the slower persistent wind flow ( Hartmann et al 1985;Brown et al 1996). The metal-deficient field giant HD 6833 (G9.5 III) also shows a fast wind ( Dupree et al 1992a).…”

Section: Singg Le Starsmentioning

confidence: 99%

VLA Observations of ζ Aurigae: Confirmation of the Slow Acceleration Wind Density Structure

et al. 2005

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Studies of the winds from single K and early M evolved stars indicate that these flows typically reach a significant fraction of their terminal velocity within the first couple of stellar radii. The most detailed spatially resolved information of the extended atmospheres of these spectral types comes from the Aur eclipsing binaries. However, the wind acceleration inferred for the evolved primaries in these systems appears significantly slower than for stars of similar spectral type. Since there are no successful theories for mass loss from K and early M evolved stars, it is important to place strong empirical constraints on potential models and determine whether this difference in acceleration is real or an artifact of the analyses. We have undertaken a radio continuum monitoring study of Aurigae ( K4 Ib + B5 V) using the Very Large Array to test the wind density model of Baade et al. that is based on Hubble Space Telescope (HST ) Goddard High Resolution Spectrograph ultraviolet spectra. Aur was monitored at centimeter wavelengths over a complete orbital cycle, and flux variations during the orbit are found to be of similar magnitude to variations at similar orbital phases in the adjacent orbit. During eclipse, the flux does not decrease, showing that the radio emission originates from a volume substantially larger than R 3 K $ (150 R ) 3 surrounding the B star. Using the one-dimensional density model of the K4 Ib primary's wind derived from HST spectral line profile modeling and electron temperature estimates from previous optical and new HST studies, we find that the predicted radio fluxes are consistent with those observed. Three-dimensional hydrodynamic simulations indicate that the accretion flow perturbations near the B star do not contribute significantly to the total radio flux from the system, consistent with the radio eclipse observations. Our radio observations confirm the slow wind acceleration for the evolved K4 Ib component. Aur's velocity structure does not appear to be typical of single stars with similar spectral types. This highlights the need for more comprehensive multiwavelength studies for both single stars, which have been sadly neglected, and other Aur systems to determine if its wind properties are typical.

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MG Emission from Hybrid-Chromosphere Stars: 1.5 Decades of Chromospheric Variability Monitoring

Cited by 15 publications

References 17 publications

The Discovery of Oxygen‐rich Chromospheres in Two Massive DQ White Dwarfs

The Discovery of Oxygen‐rich Chromospheres in Two Massive DQ White Dwarfs

Exploring pre-main-sequence variables of the ONC: the new variables

VLA Observations of ζ Aurigae: Confirmation of the Slow Acceleration Wind Density Structure

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