J/A+A/697/A201 HD 251108 spectroscopic monitoring (Fuhrmeister+, 2025)
Characterization of the hyperactive star HD 251108:
Spectroscopic monitoring and discovery of optical superflares.
Fuhrmeister B., Mittag M., Czesla S., Schmitt J.H.M.M., Delgado-Mena E.,
Tsantaki M., Robrade J., Hatzes A., Eisloeffel J., Schneider P.C.
<Astron. Astrophys. 697, A201 (2025)>
=2025A&A...697A.201F 2025A&A...697A.201F (SIMBAD/NED BibCode)
ADC_Keywords: Stars, giant ; Stars, flare ; Radial velocities ;
Effective temperatures ; Equivalent widths
Keywords: stars: activity - stars: chromospheres - stars: late-type
Abstract:
Giant stars can be magnetically active. A prominent example is HD
251108, which exhibited a giant flare recorded on 7 November 2022
at X-ray and optical wavelengths. We report on a spectroscopic
campaign monitoring this star from November 2022 to March 2024,
starting with the late phases of the giant flare and accumulating 149
medium-resolution spectra with the TIGRE telescope. HD 251108 shows
periodic variations in radial velocity (RV), which we interpret as
being caused by the star being part of a binary system, yet the
photospheric lines do not show any obvious signs of a second
component. Similar periodic changes are found in the effective
temperature and in the equivalent widths (EWs) of various
chromospheric emission lines with the same period as observed in RV,
but with a phase shift. We find these effects could be caused by a
plage rotating with the star if the star is rotating synchronously.
Since the star shows strong Hα and even HeI infrared triplet
emission outside the flare, we find it to be hyperactive, even though
the star only has moderate lithium abundance of A(Li)=1.28dex. We
further investigated archival TESS observations of HD 251108 and found
that flares with energy releases in excess of 1038 erg at optical
wavelengths are not unusual. Finally, considering the November 2022
event in a broader context, we argue that this event likely released
more than 1040 erg at optical wavelengths.
Description:
Giant stars can be magnetically active. A prominent example is
HD 251108, which exhibited a giant flare recorded on 07-11-2022 at
X-ray and optical wavelengths. We report on a spectroscopic campaign
monitoring this star from November 2022 to March 2024 starting with
the late phases of the giant flare and accumulating 149 medium
resolution spectra with the TIGRE telescope. The star shows radial
velocity variations, which are accompagnied by equivalent width
variations in H_alpha and the effective temperature.
We measure the radial velocity, the equivalent width (EW), the signal
to noise ratio, and the effective temperature in each stellar
spectrum. For the EW calculation we state the integration ranges of
the line and the reference bands in Table 1 of the paper.
Objects:
----------------------------------------------------------
RA (2000) DE Designation(s)
----------------------------------------------------------
06 04 14.99 +12 45 51.0 HD 251108 = TIC 151176998
----------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea1.dat 74 142 HD 251108 spectral characteristics
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 F12.4 d JD Julian date of observation
16- 20 F5.2 km/s RV Radial velocity
24- 27 F4.2 km/s e_RV Standard deviation of RV
32- 37 F6.2 0.1nm EWHa Equivalent width of Halpha
43- 46 F4.2 0.1nm e_EWHa Standard deviation of EWHa
51- 55 F5.1 --- S/N Signal to noise ratio
60- 65 F6.1 K Teff Effective temperature
71- 74 F4.1 K e_Teff Standard deviation of Teff
--------------------------------------------------------------------------------
Acknowledgements:
Birgit Fuhrmeister, birgit.fuhrmeister(at)uni-hamburg.de
(End) B. Fuhrmeister [Hamburg Univ., Germany], P. Vannier [CDS] 02-Apr-2025