Exploring the directly imaged HD 1160 system through spectroscopic characterization and high-cadence variability monitoring

The time variability and spectra of directly imaged companions provide insight into their physical properties and atmospheric dynamics. We present follow-up R ~ 40 spectrophotometric monitoring of red companion HD 1160 B at 2.8-4.2 μm using the double-grating 360° vector Apodizing Phase Plate (dgvAPP360) coronagraph and ALES integral field spectrograph on the Large Binocular Telescope Interferometer. We use the recently developed technique of gvAPP-enabled differential spectrophotometry to produce differential light curves for HD 1160 B. We reproduce the previously reported ~3.2 h periodic variability in archival data, but detect no periodic variability in new observations taken the following night with a similar 3.5 per cent level precision, suggesting rapid evolution in the variability of HD 1160 B. We also extract complementary spectra of HD 1160 B for each night. The two are mostly consistent, but the companion appears fainter on the second night between 3.0-3.2 μm. Fitting models to these spectra produces different values for physical properties depending on the night considered. We find an effective temperature T_eff = $2794^{+115}_{-133}$ K on the first night, consistent with the literature, but a cooler T_eff = $2279^{+79}_{-157}$ K on the next. We estimate the mass of HD 1160 B to be 16-81 M_Jup, depending on its age. We also present R = 50 000 high-resolution optical spectroscopy of host star HD 1160 A obtained simultaneously with the PEPSI spectrograph. We reclassify its spectral type to A1 IV-V and measure its projected rotational velocity $\upsilon \sin i$ = $96^{+6}_{-4}$ km s^-1. We thus highlight that gvAPP-enabled differential spectrophotometry can achieve repeatable few per cent level precision and does not yet reach a systematic noise floor, suggesting greater precision is achievable with additional data or advanced detrending techniques.