Characterizing the magnetic field and spectral variability of the rigidly rotating magnetosphere star HD 345439

Abstract

A team involved in APOGEE, one of the Sloan Digital Sky Survey III programs, recently announced the discovery of two rare rigidly rotating magnetosphere stars, HD 345439 and HD 23478. Near-infrared spectra of these objects revealed emission-line behavior identical to that previously discovered in the helium-strong star σ Ori E, which has a strong magnetic field and rotates fast. A single spectropolarimetric observation of HD 345439 with FORS 2 at the VLT in 2014 over 88 min indicated that HD 345439 may host a strong, rapidly varying magnetic field. In this work, we present the results of our spectropolarimetric monitoring of this star with FORS 2, which revealed the presence of a strong longitudinal magnetic field dominated by a dipolar component. The analysis of spectral variability indicates an opposite behaviour of He and Si lines, which is usually attributed to differences in the distribution of surface He and Si abundance spots.

The Magnetic Early B-type Stars IV: Breakout or Leakage? H$α$ emission as a diagnostic of plasma transport in centrifugal magnetospheres

“…The presence of emission in this star should however be treated as tentative. HD 345439: the discovery of CM-type infrared emission lines in this star by Eikenberry et al (2014) motivated spectroscopic and FORS2 magnetic follow-up observations by Wisniewski et al (2015) and Hubrig et al (2015Hubrig et al ( , 2017a. This is the only star in the sample for which high-resolution spectropolarimetry is not available, and the only highresolution visual spectra are the ARCES spectra published by Wisniewski et al (2015).…”

Trumpler 16-26: a new centrifugal magnetosphere star discovered via SDSS/APOGEE H-band spectroscopy

“…The final three columns provide the magnetic field measurements (see Section 2.5). The quoted 𝜙 rot were calculated using periods and emphemerides established in this paper for Tr16-26, and taken from the literature for 𝜎 Ori E (Townsend et al 2010), HD 23478 (Sikora et al 2015), and HD 345439 (Wisniewski et al 2015;Hubrig et al 2017a). In all cases, the emphemerides have been adjusted such that 𝜙 rot = 0 corresponds to an epoch of minimum 𝐵 z (as will be the convention in this paper).…”

“…Filled symbols in the bottom panel of Figure 3 are the results of phasing our Tr16-26 𝐵 z measurements to the period obtained from the TESS 𝑙𝑐. For comparison, 𝐵 z measurements are also shown for 𝜎 Ori E (Oksala et al 2012), HD 23478 (Sikora et al 2015), and HD 345439 (Hubrig et al 2017a), with the measurements of the latter two stars having been shifted vertically for clarity by +1.5 kG and −1.0 kG, respectively.…”

“…Bottom panel: The 𝐵 z measurements of Tr16-26 (filled symbols) phased by the rotation period determined from the TESS lightcurve, with the dashed curve being the best fitting sinusoid to the 𝐵 z all measurements. Unfilled symbols are 𝐵 z measurements for 𝜎 Ori E (Oksala et al 2012), HD 23478(Sikora et al 2015), and HD 345439(Hubrig et al 2017a).…”

Variability of Magnetic Hot Stars from the TESS Observations

“…The majority of the detected large-scale magnetic fields of the magnetic hot stars are stable over time spans of up to decades (e.g., Oksala et al 2012;Sikora et al 2019), and have a predominantly dipole topological structure inclined to the rotational axis, with magnetic field strengths ranging from tens of Gauss to tens of kilo-Gauss (e.g., Shultz et al 2018;Järvinen et al 2021). Strong magnetic fields have been considered to explain the particular properties of these hot stars, such as photometric variations (e.g., Oksala et al 2015;Shen et al 2023), Hα line variations (e.g., Wisniewski et al 2015;Hubrig et al 2017;Shultz et al 2020), the UV resonance line variations (e.g., Shore & Brown 1990;ud-Doula et al 2022), the X-ray properties (e.g., Wade et al 2012;Petit et al 2015), and the radio emissions (e.g., Leto et al 2017;Shultz et al 2022).…”