IAU GA XXX – Meeting of the IAU Working Group on Ap & Related Stars – Programme

Logo IAU General Assembly Vienna 2018

As previously announced, a meeting of the IAU WG on Ap & Related Stars (ApWG) will take place during the XXXth IAU General Assembly in Vienna, on Thursday, August 30, from 8:30 to 12:00 (coffee break between 10:00 and 10:30). The meeting location will be room L1. You will find below the current version of the programme of the meeting. There is still room to accommodate some additions to this programme. Should you wish to suggest such an addition (e.g., a scientific presentation), please email gmathys@eso.org.

ApWG meeting programme – June 30, 8:30–12:00

  1. Commemoration: 40 years of “A Peculiar Newsletter” (Hans-Michael Maitzen)
  2. Business meeting
    1. Report on the past triennium (2015–2018)
    2. Announcement: Election of the Organising Committee for the triennium 2018–2021
    3. Discussion: The future of the ApWG
  3. Scientific presentations (see abstracts below)
    1. HST/STIS analysis of the first main-sequence pulsar CU Vir (Jiri Krticka)
    2. Studying the anomalous atmospheric structure of magnetic rapidly oscillating Ap stars using the rare-earth element anomaly (Swetlana Hubrig)
    3. Abundance Systematics in Herbig Ae/Be Stars (Charles Cowley)
    4. Magnetic Ap stars that rotate (extremely) slowly: challenges and prospects (Gautier Mathys)

Abstracts of scientific presentations

HST/STIS analysis of the first main-sequence pulsar CU Vir (Jiri Krticka)

CU Vir has been the first main sequence star that showed regular radio pulses interpreted as coherent auroral radio emission. The star belongs to a group of hot chemically peculiar stars with variable rotational period. We study the ultraviolet spectrum of CU Vir obtained using STIS spectrograph onboard HST to search to search for the signature at the UV wavelengths of the electrons responsible of the stellar auroral radio emission and to test the theoretical model of the rotational period evolution. We use our own UV and visual photometric observations supplemented with archival data to improve our knowledge of rotational period evolution. The UV and visual light curves display the same long-term period variations supporting their common origin. New updated abundance maps provide significantly better agreement with observed flux distribution especially in far-UV region. This supports the flux redistribution from far-UV to near-UV and visual domains originating in surface abundance spots as the main cause of the flux variability in chemically peculiar stars. The upper limit of the wind mass-loss rate is about 1e-12 Mo/yr. We search for the auroral lines and for the rotationally modulated variability of interstellar lines. The radio lighthouse of CU Vir is most likely powered by very weak presumably purely metallic wind that does not leave any imprint in the spectra.

Studying the anomalous atmospheric structure of magnetic rapidly oscillating Ap stars using the rare-earth element anomaly (Swetlana Hubrig)

Recently, we used spectropolarimetric HARPS observations of the famous chemically peculiar rapidly oscillating Ap (roAp) star HD101065 (also known as Przybylski’s star) to study its magnetic and pulsational variability. As most of the previously studied roAp stars show the rare-earth element anomaly related to the vertical abundance stratification of rare earths, this anomaly was for the first time used to establish the presence of a rather strong radial magnetic field gradient of about 300G. This discovery opens a new avenue for studies of roAp stars. Acquiring high-resolution spectropolarimetric observations of roAp stars with different pulsational characteristics distributed over their rotation/magnetic periods, it will become possible for the first time to probe the optical depth of formation of spectral lines belonging to different elements and to study atmospheric depths as a function of the rotation/magnetic phase in stars with different magnetic field configurations and magnetic field strengths.

Abundance Systematics in Herbig Ae/Be Stars (Charles Cowley)

We review the systematics of abundance work on Herbig Ae/Be stars (eg. Folsom, et al. MNRAS, 442, 2072, 2012).  Roughly half of these stars show the Lambda Bootes pattern, where refractory elements are depleted relative to volatiles. The depletions are correlated with condensation temperature. Similar patterns are found in post AGB stars, in the interstellar medium, and in solar twins.  However, details of the abundance anomalies vary, suggesting complex scenarios will be needed to explain them. 

Magnetic Ap stars that rotate (extremely) slowly: challenges and prospects (Gautier Mathys)

A significant fraction of the magnetic Ap stars (several percent) have rotation periods longer than one year. Some of them must definitely have periods of the order of 300 years or longer, possibly up to 1000 years or more. The mechanisms responsible for the extreme rotational braking that these stars have undergone since their formation remain unknown. Additional observational constraints are required to guide the theoretical developments. One of the major challenges is to determine a sufficient number of the longest periods: this requires a small number of observations to be obtained over a (very) long time interval, with no immediate publishable result. On the other hand, until now, very little is known about extremely slow rotation in Ap stars with magnetic fields weaker than 2.0 kG, which do not show magnetically split lines in visible range spectra. The new generation of high-resolution infrared spectrographs opens the prospect of resolving magnetically split lines in those weak field stars, as well as in stronger field stars with moderately slow rotation. Both will provide additional valuable insight towards understanding the connection between rotation and magnetic field in Ap stars.