Coronal and chromospheric emission in A-type stars

Abstract

Cool stars on the main sequence generate X-rays from coronal activity, powered by a convective dynamo. With increasing temperature, the convective envelope becomes smaller and X-ray emission fainter. We present Chandra/HRC-I observations of four single stars with early A spectral types. Only the coolest star of this sample, ${\tau }^3$ Eri ($T_{\mathrm{eff}}\approx 8,000$ K), is detected with $\log (L_X/L_{\mathrm{bol}})=-7.6$ while the three hotter stars ($T_{\mathrm{eff}}\ge 8,000$ K), namely $\delta$ Leo, $\beta$ Leo, and $\iota$ Cen, remain undetected with upper limits $\log (L_X/L_{\mathrm{bol}})<-8.4$. The drop in X-ray emission thus occurs in a narrow range of effective temperatures around $\sim 8100$ K and matches the drop of activity in the C III and O VI transition region lines.

11 pages, 3 figures, accepted by AJ

References in corpus (23)

• Array Programming with NumPy
• The NumPy array: a structure for efficient numerical computation
• The Gaia mission
• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• astroquery: An Astronomical Web-Querying Package in Python
• CHIANTI -- an atomic database for emission lines -- Paper XVI: Version 10, further extensions
• Imaging the Surface of Altair
• Interferometric Observations of Rapidly Rotating Stars
• The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets
• Imaging and Modeling Rapidly Rotating Stars: Alpha Cephei and Alpha Ophiuchi
• The first high-resolution X-ray spectrum of a Herbig Star: The case of AB Aurigae
• A Direct Imaging Survey of Spitzer detected debris disks: Occurrence of giant planets in dusty systems
• Precise Dynamical Masses and Orbital Fits for $\beta$ Pic b and $\beta$ Pic c
• MOBSTER - II. Identification of rotationally variable A stars observed with \emph{TESS} in Sectors 1 to 4
• Jets, accretion, coronae and all that: The enigmatic X-rays from the Herbig star HD 163296
• Do A-type stars flare?
• Altair - the 'hottest' magnetically active star in X-rays
• Stellar X-ray activity across the Hertzsprung-Russell diagram. I. Catalogs
• Burn Out or Fade Away? On the X-ray and Magnetic Death of Intermediate Mass Stars
• Determining X-Ray Source Intensity and Confidence Bounds in Crowded Fields
• A decade of radial-velocity monitoring of Vega and new limits on the presence of planets
• O VI Observations of the Onset of Convection Zones in Main-Sequence A Stars
• The HOSTS survey: evidence for an extended dust disk and constraints on the presence of giant planets in the Habitable Zone of $\beta$ Leo