ALMA millimetre-wavelength imaging of HD 138965: New constraints on the debris dust composition and presence of planetary companions

J. P. Marshall; S. Hengst; A. Trejo-Cruz; C. del Burgo; J. Milli; M. Booth; J. C. Augereau; E. Choquet; F. Y. Morales; P. Thébault; F. Kemper; V. Faramaz-Gorka; G. Bryden

paper

ALMA millimetre-wavelength imaging of HD 138965: New constraints on the debris dust composition and presence of planetary companions

arXiv:2506.11726

Abstract

HD 138965 is a young A type star and member of the nearby young Argus association. This star is surrounded by a broad, bright debris disc with two temperature components that was spatially resolved at far-infrared wavelengths by Herschel. Here we present ALMA millimetre-wavelength imaging of the cool outer belt. These reveal its radial extent to be $15 0_{- 7}^{+ 10}$ au with a width ( $σ$ ) of 49 $_{- 6}^{+ 7}$ au ( $Δ R / R$ = 0.77), at a moderate inclination of 49$\fdeg$9^{+3.3}_{-3.7} $. D u e t o t h e l imi t e d an g u l a r r eso l u t i o n, s i g na l - t o - n o i se, an d in c l ina t i o n w e ha v e n oco n s t r ain t o n t h e d i s c^{'} s v er t i c a l sc a l e h e i g h t . W e m o d e l l e d t h e d i sce mi ss i o n w i t hb o t h g r a v i t a t i o na l an d r a d ia t i o n f or ces a c t in g o n t h e d u s t g r ain s . A s t h e inn er b e l t ha s n o t b ee n s p a t ia l l y r eso l v e d, w e f i x e d i t sr a d i u s an d w i d t h p r i or t o m o d e l l in g t h eo u t er b e l t . W e f in d a s t r o n o mi c a l s i l i c a t e i s t h e b es t f i t f or t h e d u s t co m p os i t i o n . H o w e v er, w eco u l d n o t r e j ec tp oss ib l esce na r i os w h er e t h er e a r e a tl e a s t 10% w a t er - i ce in c l u s i o n s . C o mbinin g t h es p a t ia l l y r eso l v e d ima g in g b y A L M A w i t hn o n - d e t ec t i o na t o pt i c a l w a v e l e n g t h s b y H S T, w eo b t aina l imi t o n t h esc a tt er in g a l b e d o$ ω\leq 0.09 $f or t h e d e b r i s d u s t in t h eo u t er b e l t . A na l y s i so f t h eo u t er b e l t^{'} s a r c hi t ec t u r e in co nj u n c t i o n w i t h s im pl es t i r r in g m o d e l s pl a ces ama ss l imi t o f$ 2.3~\pm~0.4 M_{\rm Jup} $o na co m p ani o nin t er i or t o t h e b e l t ($ a \leq 78$ au), a factor of two improvement over constraints from high contrast imaging.

14 pages, 4 figures, 5 tables, 2 appendices, accepted for publication in MNRAS