Carina High-contrast Imaging Project for massive Stars (CHIPS)

Abstract

Context. Most massive stars belong to multiple systems, yet the formation process leading to such high multiplicity remains insufficiently understood. To help constrain the different formation scenarios that exist, insights into the low-mass end of the companion mass function of such stars is crucial. However, this is a challenging endeavour as (sub-)solar mass companions at angular separations (ρ) below 1″ (corresponding to 1000–3000 au in nearby young open clusters and OB associations) are difficult to detect due to the large brightness contrast with the central star. Aims. With the Carina High-contrast Imaging Project of massive Stars (CHIPS), we aim to obtain statistically significant constraints on the presence and properties of low-mass companions around massive stars in a previously unreachable observing window (Δmag ≳ 10 at ρ ≲ 1″). In the second paper of the series, we focus on the Trumpler 14 cluster, which harbours some of the youngest and most massive O-type stars in the Milky Way. Methods. We obtained VLT-SPHERE observations of seven O-type objects in Trumpler 14 using IRDIFS_EXT mode. These provide us with a 12″ × 12″ field of view (approximately ((3 × 3)×104 au) centred on each O star and allow us to search for companions at separations larger than 0″​​.15 (approx. 360 au) and down to magnitude contrast > 10 mag in the near-infrared. We used angular and spectral differential imaging along with Point Spread Function (PSF) fitting to detect sources and measure their flux relative to that of the central object. We then used grids of ATLAS9 and PHOENIX Local Thermodynamic Equilibrium (LTE) atmosphere models combined with (pre-)main-sequence evolutionary tracks to estimate the mass of the detected candidate companions. Results. We detected 211 sources with near-infrared magnitude contrast in the range of 2–12. Given the large surface number density of stars in Trumpler 14, one cannot reliably distinguish between cluster members and genuine companions for most of the detected sources. The closest companion, at only 0″​​.26, is characterised as a 1.4 M⊙ star with an age of 0.6 Myr, in excellent agreement with previous age estimates for Tr 14. The mass function peaks at about 0.4 M⊙ and presents a dearth of stars in the 0.5–0.8 M⊙ mass range compared to previous estimates of the initial mass function in Tr 14. While statistically significant, part of these differences may result from contamination of the K-band fluxes by circumstellar material. Conclusions. SPHERE is clearly suitable to probe the low-mass end of the mass function in the vicinity of massive stars. Follow-up SPHERE observations to obtain the full Y to K spectral energy distribution would allow for better constraints on the masses of the detected sources, and to confirm (or invalidate) the curious mass function that we derived for low-mass stars in the vicinity of the O-type objects in Trumpler 14.

Probing the low-mass end of the companion mass function for O-type stars

“…29 and for which the fits of the K-band magnitudes is consistent with masses of 0.25−0.4 and 0.2−0.4 M , respectively, with ages between 0.3 and 1.5 Myr. A more detailed analysis of the system, including the reanalysis of the B visual companion (classified as B0.2 V by Maíz Apellániz et al 2022) will be presented in Rainot et al (2022).…”

The onset of stellar multiplicity in massive star formation: A search for low-mass companions of massive young stellar objects with L′-band adaptive optics imaging

“…We further investigate our findings for a specific class of objects: massive stars. To do so, we relax the evolutionary stage parameter and compare our results to those of different studies (Apai et al 2007;Sana et al 2014;Gravity Collaboration et al 2018;Pomohaci et al 2019;Koumpia et al 2021;Rainot et al 2022;Bordier et al 2022). The results are shown in Fig.…”

VIP: A Python package for high-contrast imaging

“…The features implemented in VIP as of 2017 are described in Gomez Gonzalez et al ( 2017). Since then, the package has been widely used by the high-contrast imaging community for the discovery of low-mass companions (Hirsch et al, 2019;Milli, Hibon, et al, 2017;Ubeira-Gabellini et al, 2020), their characterization (Christiaens et al, 2019(Christiaens et al, , 2018Delorme et al, 2017;Wertz et al, 2017), the study of planet formation (Maucó et al, 2020;Reggiani et al, 2018;Ruane et al, 2017;Toci et al, 2020), the study of high-mass star formation (Rainot et al, 2022(Rainot et al, , 2020, the study of debris disks (Milli, Vigan, et al, 2017;Milli et al, 2019), or the development of new high-contrast imaging algorithms (Dahlqvist et al, 2020(Dahlqvist et al, , 2021Gomez Gonzalez et al, 2018;Pairet et al, 2021).…”