GaiaDR2 study of Herbig Ae/Be stars

Abstract

Aims. We use Gaia Data Release 2 (DR2) to place 252 Herbig Ae/Be stars in the HR diagram and investigate their characteristics and properties. Methods. For all known Herbig Ae/Be stars with parallaxes in Gaia DR2, we collected their atmospheric parameters and photometric and extinction values from the literature. To these data we added near-and mid-infrared photometry, collected Hα emission line properties such as equivalent widths and line profiles, and their binarity status. In addition, we developed a photometric variability indicator from Gaia's DR2 information.Results. We provide masses, ages, luminosities, distances, photometric variabilities and infrared excesses homogeneously derived for the most complete sample of Herbig Ae/Be stars to date. We find that high mass stars have a much smaller infrared excess and have much lower optical variabilities compared to lower mass stars, with the break at around 7M . Hα emission is generally correlated with infrared excess, with the correlation being stronger for infrared emission at wavelengths tracing the hot dust closest to the star. The variability indicator as developed by us shows that ∼25% of all Herbig Ae/Be stars are strongly variable. We observe that the strongly variable objects display doubly peaked Hα line profiles, indicating an edge-on disk.Conclusions. The fraction of strongly variable Herbig Ae stars is close to that found for A-type UX Ori stars. It had been suggested that this variability is in most cases due to asymmetric dusty disk structures seen edge-on. The observation here is in strong support of this hypothesis. Finally, the difference in dust properties occurs at 7M , while various properties traced at UV/optical wavelengths differ at a lower mass, 3M . The latter has been linked to different accretion mechanisms at work whereas the differing infrared properties and photometric variabilities are related to different or differently acting (dust-)disk dispersal mechanisms.

The accretion rates and mechanisms of Herbig Ae/Be stars

“…Columns 2-9 are effective temperature, surface gravity, visual extinction, distance, radius, luminosity, mass and age respectively. Distance D in column 5 is obtained from Vioque et al (2018). Figure 4 demonstrates all these HAeBes (21 + 62) placed in the HR diagram.…”

“…They are also included in Figure 4. Hα equivalent widths are provided for most objects in Vioque et al (2018, their table 1 and table 2) with references. Spectra for 14 objects without Hα data in the V18 sample were found in the ESO Science Archive Facility.…”

“…The stellar radii and surface gravities were calculated using the temperatures, luminosities and masses provided in V18. The intrinsic equivalent widths were mea- sured from BOSZ models for the temperature provided in Vioque et al (2018, table 1 and table 2) and the calculated surface gravity. This will enable us to compute mass accretion rates for a further 85 objects below.…”

Mass constraints for 15 protoplanetary discs from HD 1–0

“…We also show in Figure 6 three somewhat older stars of similar mass (HD 95086, β Pic, and HR 8799) and their planets; standard disk mass estimates for stars of 1.5 and 3 M based on M dust relations from Pascucci et al (2016) and scaled up with ∆ g/d = 100; and a shaded log-scale histogram of the mass distribution of known planets around early-type stars 1 . Stellar masses are from the GAIA DR2 analysis by Vioque et al (2018), and from David & Hillenbrand (2015, β Pic) and Stassun et al (2018, HD 95086). Planet masses for individual systems are plotted as cumulative bars, with the highest-mass planet at the base.…”

“…We Marois et al (2008Marois et al ( , 2010. Individual stellar masses are from Rhee et al (2007), David & Hillenbrand (2015), Stassun et al (2018), and Vioque et al (2018).…”