Intermediate-mass Stars Research Articles

Formation of giant planets around intermediate-mass stars

ABSTRACT To understand giant planet formation, we need to focus on host stars close to $M_{\star }{=}1.7\, \rm M_\odot$, where the occurrence rate of these planets is the highest. In this initial study, we carry out pebble-driven core accretion planet formation modelling to investigate the trends and optimal conditions for the formation of giant planets around host stars in the range of $1\!-\!2.4\ \rm {\rm M}_{\odot }$. We find that giant planets are more likely to form in systems with a larger initial disc radius; higher disc gas accretion rate; pebbles of ∼millimeter in size; and birth location of the embryo at a moderate radial distance of ∼10 au. We also conduct a population synthesis study of our model and find that the frequency of giant planets and super-Earths decreases with increasing stellar mass. This contrasts the observational peak at $1.7\, \rm M_\odot$, stressing the need for strong assumptions on stellar mass dependencies in this range. Investigating the combined effect of stellar mass dependent disc masses, sizes, and lifetimes in the context of planet population synthesis studies is a promising avenue to alleviate this discrepancy. The hot-Jupiter occurrence rate in our models is $\sim 0.7\!-\!0.8~{{\ \rm per\ cent}}$ around $1\, \rm M_\odot$ – similar to RV observations around Sun-like stars, but drastically decreases for higher mass stars.

Asteroseismology Sheds Light on the Origin of Carbon-deficient Red Giants: Likely Merger Products and Linked to the Li-rich Giants

Carbon-deficient red giants (CDGs) are a peculiar class of stars that have eluded explanation for decades. We aim to better characterize CDGs by using asteroseismology (Kepler, TESS) combined with spectroscopy (APOGEE, LAMOST), and astrometry (Gaia). We discovered 15 new CDGs in the Kepler field, and confirm that CDGs are rare, as they are only 0.15% of our background sample. Remarkably, we find that our CDGs are almost exclusively in the red clump (RC) phase. Asteroseismic masses reveal that our CDGs are primarily low-mass stars (M ≲ 2 M ⊙), in contrast to previous studies, which suggested they are intermediate mass (M = 2.5–5.0 M ⊙) based on HR diagrams. A very high fraction of our CDGs (50%) are also Li-rich giants. We observe a bimodal distribution of luminosity in our CDGs, with one group having normal RC luminosity and the other being a factor of 2 more luminous than expected for their masses. We find demarcations in chemical patterns and luminosities, which lead us to split them into three groups: (i) normal-luminosity CDGs, (ii) overluminous CDGs, and (iii) overluminous highly polluted CDGs. We conclude that a merger of a helium white dwarf with a red giant branch star is the most likely scenario for the two groups of overluminous stars. Binary mass-transfer from intermediate-mass asymptotic giant branch stars is a possibility for the highly polluted overluminous group. For the normal-luminosity CDGs, we cannot distinguish between core He-flash pollution or lower-mass merger scenarios. Due to the overlap with the CDGs, Li-rich giants may have similar formation channels.

A comparative study of three modes of s-process nucleosynthesis in extremely metal-poor AGB stars

Abstract Carbon-enhanced metal-poor (CEMP) stars in the Galactic halo have a wide range of neutron-capture element abundance patterns. To identify their origin, we investigate three modes of s-process nucleosynthesis that have been proposed to operate in extremely metal-poor asymptotic giant branch (AGB) stars: convective 13C burning, which occurs when hydrogen is engulfed by helium-flash convection in low-mass AGB stars; convective 22Ne burning, which occurs in helium-flash convection of intermediate-mass AGB stars; and radiative 13C burning, which occurs in the 13C pocket that is formed during inter-pulse periods. We show that the production of s-process elements per iron seed (s-process efficiency) does not depend on metallicity below [Fe$/$H] = −2, because 16O in the helium zone dominates the neutron poison. The convective 13C mode can produce a variety of s-process efficiencies for Sr, Ba, and Pb, including the maxima observed among CEMP stars. The 22Ne mode only produces the lowest end of s-process efficiencies among CEMP models. We show that the combination of these two modes can explain the full range of observed enrichment of s-process elements in CEMP stars. In contrast, the 13C pocket mode can hardly explain the high level of enrichment observed in some CEMP stars, even if considering star-to-star variations of the mass of the 13C pocket. These results provide a basis for discussing the binary mass transfer origin of CEMP stars and their subgroups.

Aluminium-26 production in low- and intermediate-mass binary systems

ABSTRACT Aluminium-26 is a radioactive isotope which can be synthesized within asymptotic giant branch (AGB) stars, primarily through hot bottom burning. Studies exploring 26Al production within AGB stars typically focus on single-stars; however, observations show that low- and intermediate-mass stars commonly exist in binaries. We use the binary population synthesis code binary_c to explore the impact of binary evolution on 26Al yields at solar metallicity both within individual AGB stars and a low/intermediate-mass stellar population. We find the key stellar structural condition achieving most 26Al overproduction is for stars to enter the thermally pulsing AGB (TP-AGB) phase with small cores relative to their total masses, allowing those stars to spend abnormally long times on the TP-AGB compared to single-stars of identical mass. Our population with a binary fraction of 0.75 has an 26Al weighted population yield increase of 25 per cent compared to our population of only single-stars. Stellar-models calculated from the Mt Stromlo/Monash Stellar Structure Program, which we use to test our results from binary_c and closely examine the interior structure of the overproducing stars, support our binary_c results only when the stellar envelope gains mass after core-He depletion. Stars which gain mass before core-He depletion still overproduce 26Al, but to a lesser extent. This introduces some physical uncertainty into our conclusions as 55 per cent of our 26Al overproducing stars gain envelope mass through stellar wind accretion onto pre-AGB objects. Our work highlights the need to consider binary influence on the production of 26Al.

Dust from evolved stars: a pilot analysis of the AGB to PN transition

ABSTRACT We present a novel approach to address dust production by low- and intermediate-mass stars. We study the asymptotic giant branch (AGB) phase, during which the formation of dust takes place, from the perspective of post-AGB and planetary nebula (PN) evolutionary stage. Using results from stellar evolution and dust formation modelling, we interpret the spectral energy distribution of carbon-dust-rich sources currently evolving through different evolutionary phases, believed to descend from progenitors of similar mass and chemical composition. Comparing the results of different stages along the AGB to PNe transition, we can provide distinct insights on the amount of dust and gas released during the very late AGB phases. While the post-AGB traces the history of dust production back to the tip of the AGB phase, investigating the PNe is important to reconstruct the mass-loss process experienced after the last thermal pulse. The dust surrounding the post-AGB was formed soon after the tip of the AGB. The PNe dust-to-gas ratio is ∼10−3, 2.5 times smaller than what expected for the same initial mass star during the last AGB interpulse, possibly suggesting that dust might be destroyed during the PN phase. Measuring the amount of dust present in the nebula can constrain the capacity of the dust to survive the central star heating.

Survival of fossil fields during the pre-main sequence evolution of intermediate-mass stars

Context. Chemically peculiar Ap and Bp stars host strong large-scale magnetic fields in the range of 200 G up to 30 kG, which are often considered to be the origin of fossil magnetic fields. Aims. We assess the evolution of such fossil fields during the star formation process and the pre-main sequence evolution of intermediate stars based on: fully convective models, models including a transition to a radiative protostar, and models with a radiative core. We also examine the implications of the interaction between the fossil field and the core dynamo. Methods. We employed analytic and semi-analytic calculations, combined with current observational constraints. Results. For fully convective models, we show that magnetic field decay via convection can be expected to be very efficient for realistic parameters of turbulent resistivities. Based on the observed magnetic field strength-density relation, as well as the expected amount of flux loss due to ambipolar diffusion, it appears unlikely that convection could be suppressed via strong enough magnetic fields. On the other hand, a transition from a convective to a radiative core could very naturally explain the survival of a significant amount of flux, along with the presence of a critical mass. We show that in some cases, the interaction of a fossil field with a core dynamo may further lead to changes in the surface magnetic field structure. Conclusions. In the future, it will be important to understand in more detail how the accretion rate evolves as a function of time during the formation of intermediate-mass protostars, including its impact on the protostellar structure. The latter may even allow us to derive quantitative predictions concerning the expected population of large scale magnetic fields in radiative stars.

A Systematic Observational Study on Galactic Interstellar Ratio 18O/17O. II. C18O and C17O J = 2–1 Data Analysis

To investigate the relative amount of ejecta from high-mass versus intermediate-mass stars and to trace the chemical evolution of the Galaxy, we have performed a systematic study of Galactic interstellar 18O/17O ratios toward a sample of 421 molecular clouds with IRAM 30 m and the 10 m Submillimeter Telescope, covering a galactocentric distance range of ∼1–22 kpc. The results presented in this paper are based on the J = 2–1 transition and encompass 364 sources showing both C18O and C17O detections. The previously suggested 18O/17O gradient is confirmed. For the 41 sources detected with both facilities, good agreement is obtained. A correlation of the 18O/17O ratios with heliocentric distance is not found, indicating that beam dilution and linear beam sizes are not relevant. For the subsample of IRAM 30 m high-mass star-forming regions with accurate parallax distances, an unweighted fit gives 18O/17O = (0.12 ± 0.02)R GC + (2.38 ± 0.13) with a correlation coefficient of R = 0.67. While the slope is consistent with our J = 1–0 measurement, the ratios are systematically lower. This should be caused by larger optical depths of C18O 2–1 lines with respect to the corresponding 1–0 transitions, which is supported by RADEX calculations and the fact that C18O/C17O is positively correlated with 13CO/C18O. When we consider that optical depth effects with C18O J = 2–1 typically reach an optical depth of ∼0.5, the corrected 18O/17O ratios from the J = 1–0 and J = 2–1 lines are consistent. A good numerical fit to the data is provided by the MWG-12 model, which includes both rotating stars and novae.

Galactic Chemical Evolution with the short lived radioisotopes \(^{53}\textbf{Mn}\), \(^{60}\textbf{Fe}\), \(^{182}\textbf{Hf}\), and \(^{244}\textbf{Pu}\)

Modelling the Galactic chemical evolution (GCE) of short-lived radioisotopes (SLRs, with half-lives of the order of million years) can provide timing information on recent nucleosynthesis. The knowledge of their spatial distribution throughout the interstellar medium (ISM) is crucial. We are using a three-dimensional GCE model to investigate the evolution of four SLRs: \(^{53}\)Mn from supernovae of type Ia (SNeIa), \(^{60}\)Fe from core-collapse supernovae (CCSNe), \(^{182}\)Hf from stellar winds from intermediate mass stars (IMSs), and \(^{244}\)Pu from neutron star mergers (NSMs) to explain the recent (within the last $\approx 1 -- 20$ Myr) deposition of live SLRs into deep-sea reservoirs. We find that although these SLRs are produced at very different nucleosynthetic sites, they are deposited on Earth conjointly.

Calibrating angular momentum transport in intermediate-mass stars from gravity-mode asteroseismology

Context. The physical mechanisms driving the transport of angular momentum in stars are not fully understood, as current models cannot explain the observed stellar rotation profiles across all stages of evolution. Aims. By making use of pulsating F-type dwarfs, we aim to (i) observationally calibrate the efficiency of angular momentum transport, assuming a constant uniform viscosity, and (ii) test how well state-of-the-art rotating stellar models with angular momentum (AM) transport by rotationally induced processes can explain observed rotation profiles. In both cases, the aim is to simultaneously reproduce the measured near-core rotation and core-to-surface rotation ratio. Methods. Asteroseismic modelling is applied to a sample of seven slowly rotating pulsators in order to derive (core) masses and ages from their gravity-mode oscillations. This work focuses on the main sequence (MS), using models that start with an initial uniform rotation frequency at the start of core-hydrogen burning, which is a free parameter. Two treatments of AM transport are considered: (i) a constant uniform viscosity, and (ii) rotationally induced processes (including the Spruit-Tayler dynamo). Next, the initial rotation frequency of each star is derived from the observed present-day near-core rotation frequency for both treatments. Results. Asteroseismic modelling of gravity mode periods reveals that all seven slowly rotating stars (one of which is not further modelled) in the sample are near the end of core-hydrogen burning. To explain the near-core rotation rate at the inferred age, initial rotation frequencies at the zero-age main sequence need to be below 10% of the initial critical break-up frequency. The derived initial rotation frequencies are consistent with previous works. Conclusions. A diffusive approximation of angular momentum transport can in general explain the observed rotation profiles of the six slowly rotating F-type dwarfs for average values of the viscosity of between 2 × 105 and 5 × 107 cm2 s−1 or when the viscosity is computed from rotationally induced mechanisms. Yet, for three stars in the sample, the core-to-surface rotation fraction from rotationally induced mechanisms is predicted to be higher than observed.

A large sample of newly identified carbon-deficient red giants from APOGEE

ABSTRACT Based on the Apache Point Observatory Galactic Evolution Experiment survey we conducted a search for carbon-deficient red giants (CDGs). We found 103 new CDGs, increasing the number in the literature by more than a factor of 3. CDGs are very rare, representing 0.03 per cent of giants. They appear as an extended tail off the normal carbon distribution. We show that they are found in all components of the Galaxy, contrary to previous findings. The location of CDGs in the Hertzsprung–Russell diagram (HRD) shows that they are primarily intermediate-mass stars ($2-4~\rm {M}_{\odot }$). Their extended distribution may indicate that CDGs can also sometimes have $M \lt 2.0~\rm {M}_{\odot }$. We attempted to identify the evolutionary phases of the CDGs using stellar model tracks. We found that the bulk of the CDGs are likely in the subgiant branch or red clump phase, whereas other CDGs may be in the red giant branch or early asymptotic giant branch phases. Degeneracy in the HRD makes exact identification difficult. We examined their C, N, and O compositions and confirmed previous studies showing that the envelope material has undergone extensive hydrogen burning through the CN(O) cycle. The new-CDGs have [C+N+O/Fe] that generally sum to zero, indicating that they started with scaled-solar composition. However, the previously known-CDGs generally have [C+N+O/Fe] > 0.0, indicating that some He-burning products were added to their envelopes. As to the site(s) in which this originally occurred, we do not find a convincing solution.

Hidden Companions to Intermediate-mass Stars. X. Solving for the Mass Ratio in the Spectroscopic Binary Zubenelgenubi = α 2 Librae*

Abstract Zubenelgenubi = α 2 Librae is a nearby double-lined spectroscopic binary that forms a quadruple system with α 1 Librae. The radial velocity amplitude for the rapidly rotating primary is subject to a systematic uncertainty and as a result only a lower limit q = 0.81 to the mass ratio has been previously reported. Here we present a VLTI/GRAVITY interferometric observation of Zubenelgenubi in which we measured a K band flux ratio of 74.7%, resulting in isochrone masses M Aa = 1.95 M ⊙ and M Ab = 1.79 M ⊙ (q = 0.92). The fact that the projected rotational velocities differ by a factor of three despite the similar masses suggests that the stellar spin axes are significantly misaligned in spite of the small semimajor axis a = 0.52 au or alternatively that the primary is a merger product.

Hidden Companions to Intermediate-mass Stars. IX. Discovery of a 1.5 M ⊙, 1 au Companion to the Primary within the Multiple HIP 57606* *Based on observations collected at the European Southern Observatory, Chile, Program ID 111.24UP.001.

HIP 57606 is an intermediate-mass a ∼ 88 au visual binary (A+B) that also has 680 au (C) and a 120,000 au (D) companions. Here we report on a VLTI/GRAVITY interferometric observation that revealed that the primary star A is itself a close binary with a 83% K band flux ratio companion at a projected separation ρ = 14.8 mas ↔ 1.0 au. Through isochrone fitting we find masses M Aa = 1.58M ⊙, M Ab = 1.49M ⊙ and M B = 1.15M ⊙ and an age 1 Gyr for the inner triple. The latter will evolve to become a double or triple white dwarf system within about 6 Gyr and which will be under the dynamical influence of the outer companion C.

Photometric determination of rotation axis inclination, rotation rate, and mass of rapidly rotating intermediate-mass stars

Context. Intermediate-mass stars are often fast rotators, and hence are centrifugally flattened and notably affected by gravity darkening. To analyse this kind of stars properly, one must resort to 2D models to compute the visible radiative flux and to take the geometrical effect of the star inclination into account. Aims. Assuming a given stellar age and chemical composition, our aim is to derive the mass and rotation rates of main sequence fast rotating stars, along with their inclination, from photometric quantities influenced by gravity darkening. Methods. We chose three observables that vary with mass, rotation, and inclination: the temperature derived by the infrared flux method TIRFM, the Strömgren c1 index, and a second index c2 built in the same way as the c1 index, but sensitive to the UV side of the Balmer jump. These observables are computed from synthetic spectra produced with the PHOENIX code and rely on a 2D stellar structure from the ESTER code. These quantities are computed for a grid of models in the range 2–7 M⊙, and rotation rates from 30% to 80% of the critical rate. Then, for any triplet (TIRFM, c1, c2), we try to retrieve the mass, rotation rate, and inclination using a Levenberg-Marquardt scheme, after a selection step to find the most suitable starting models. Results. Hare-and-hound tests showed that our algorithm can recover the mass, rotation rate, and inclination with a good accuracy. The difference between input and retrieved parameters is negligible for models lying on the grid and is less than a few percent otherwise. An application to the real case of Vega showed that the u filter is located in a spectral region where the modelled and observed spectra are discrepant, and led us to define a new filter. Using this new filter and subsequent index, the Vega parameters are also retrieved with satisfactory accuracy. Conclusions. This work opens the possibility to determine the fundamental parameters of rapidly rotating early-type stars from photometric space observations.

Hidden Companions to Intermediate-mass Stars. VIII. Discovery of a 0.6 M ⊙, 1.7 au Companion to Albali = ϵ Aquarii* *Based on observations collected at the European Southern Observatory, Chile, Program ID 111.24UP.001.

A large portion of the visually brightest stars in the night sky are late B to early A-type stars yet our knowledge of their multiplicity is incomplete. Here we report the discovery of a companion to the nearby star Albali (HIP 102618 = ϵ Aquarii), based on a VLTI/GRAVITY interferometric observation. The companion is at a projected separation ρ = 26 mas ↔ 1.7 au and has a K band flux ratio of 0.7%. Through isochrone fitting we find that Albali A is a 400 Myr old 2.8M ⊙ subgiant that has recently evolved off the main sequence, while the newly discovered Albali B is a 0.6 M ⊙ K dwarf. Further astrometric monitoring is needed in order to assess how strongly the stars are expected to interact as the primary expands.

Hidden Companions to Intermediate-mass Stars. VII. Discovery of a 0.76 M ⊙, 39 au Companion to the Ap Star HIP 88866 = π Pavonis* *Based on observations collected at the European Southern Observatory, Chile, Program ID 111.24UP.001.

HIP 88866 = π Pavonis is a nearby chemically peculiar Ap star. Here we report the discovery of a companion with an H band contrast ΔH = 3.63 at a projected separation ρ = 959 mas ↔ 39 au based on the acquisition camera image of a VLTI/GRAVITY observation. Isochrone fitting yields masses M A = 1.80 M ⊙ and M B = 0.76 M ⊙ and an age of 1.4 Gyr. However, even for a face-on orbit the companion cannot fully account for the GaiaDR3-Hipparcos proper motion change of π Pav. We present constraints on the nature and location of a putative additional closer companion based on the lack of its detection in the interferometric data.

Early Results from GLASS–JWST. XXI. Rapid Asembly of a Galaxy at z = 6.23 Revealed by Its C/O Abundance

The abundance of carbon relative to oxygen (C/O) is a promising probe of star formation history in the early universe, as the ratio changes with time due to production of these elements by different nucleosynthesis pathways. We present a measurement of (stat) ±0.15 (sys) in a z = 6.23 galaxy observed as part of the GLASS–JWST Early Release Science Program. Notably, we achieve good precision thanks to the detection of the rest-frame ultraviolet O iii], C iii], and C iv emission lines delivered by JWST/NIRSpec. The C/O abundance is ∼0.8 dex lower than the solar value and is consistent with the expected yield from core-collapse supernovae, indicating that longer-lived intermediate-mass stars have not fully contributed to carbon enrichment. This in turn implies rapid buildup of a young stellar population with age ≲100 Myr in a galaxy seen ∼900 Myr after the big bang. Our chemical abundance analysis is consistent with spectral energy distribution modeling of JWST/NIRCam photometric data, which indicates a current stellar mass and specific star formation rate ≃20 Gyr−1. These results showcase the value of chemical abundances and C/O in particular to study the earliest stages of galaxy assembly.

Feasibility of structure inversions for gravity-mode pulsators

Context. Gravity-mode asteroseismology has significantly improved our understanding of mixing in intermediate mass stars. However, theoretical pulsation periods of stellar models remain in tension with observations, and it is often unclear how the models of these stars should be further improved. Inversions provide a path forward by directly probing the internal structure of these stars from their pulsation periods, quantifying which parts of the model are in need of improvement. This method has been used with success in the case of solar-like pulsators, but has not yet been applied to main-sequence gravity-mode pulsators. Aims. Our aim is to determine whether structure inversions for gravity-mode pulsators are feasible. We focus on the case of slowly rotating slowly pulsating B-type (SPB) stars. Methods. We computed and analyzed dipole mode kernels for three variables pairs: (ρ, c), (N2, c), and (N2, ρ). We assessed the potential of these kernels by predicting the oscillation frequencies of a model after perturbing its structure. We then tested two inversion methods, regularized least squares (RLS) and subtractive optimally localized averages (SOLA), using a model grid computed with the MESA stellar evolution code and the GYRE pulsation code. Results. We find that changing the stellar structure affects the oscillation frequencies in a nonlinear way. The oscillation modes for which this nonlinear dependency is the strongest are in resonance with the near-core peak in the buoyancy frequency. The near-core region of the star can be probed with SOLA, while RLS requires fine tuning to obtain accurate results. Both RLS and SOLA are strongly affected by the nonlinear dependencies on the structure differences, as these methods are based on a first-order approximation. These inversion methods need to be modified for meaningful applications of inversions to SPB stars. Conclusions. Our results show that inversions of gravity-mode pulsators are possible in principle, but that the typical inversion methods developed for solar-like oscillators are not applicable. Future work should focus on developing nonlinear inversion methods.

Optical Forbidden Emission Line Spectro-astrometry of T CrA: Evidence for a Multiple System and Multiple Jets* * Based on data collected by UVES 089.C-0299(A) observations at the VLT on Cerro Paranal (Chile), which is operated by the European Southern Observatory (ESO).

Spectro-astrometry is applied to echelle spectra of the young intermediate-mass star T CrA. The aim is to better understand the origin of the [O i] and [S ii] emission from T CrA and further explore the usefulness of spectro-astrometry in the search for a reliable tracer of MHD disk winds. The analysis reveals a small-scale curved jet in an east–west direction and inclined parallel to the plane of the sky. It is the inclination of this jet that led to the classification of the forbidden emission lines as a low-velocity component. Thus, spectro-astrometry highlights here that for close to edge-on disks spatial information is necessary. The position angle of the jet is not perpendicular to the position angle of the accretion disk nor does it agree with older observations of outflows likely driven by T CrA. The mass outflow rate of 5–10 × 10−8 M ⊙ yr−1 is within the range for intermediate-mass stars. We conclude that more than one outflow is driven by the T CrA system and that the curvature seen in the first detection of an outflow from T CrA and in the data presented here is likely due to the multiplicity of the system.

Sodium enhancement in evolved cataclysmic variables

ABSTRACT We present follow-up spectroscopy of 21 cataclysmic variables (CVs) with evolved secondaries and ongoing or recently terminated mass transfer. Evolutionary models predict that the secondaries should have anomalous surface abundances owing to nuclear burning in their cores during their main-sequence evolution and subsequent envelope stripping by their companion white dwarfs. To test these models, we measure sodium (Na) abundances of the donors from the Fraunhofer ‘D’ doublet. Accounting for interstellar absorption, we find that all objects in our sample have enhanced Na abundances. We measure 0.3 dex ≲ [Na/H] ≲ 1.5 dex across the sample, with a median [Na/H] = 0.956 dex, i.e. about an order of magnitude enhancement over solar values. To interpret these values, we run Modules for Experiments in Stellar Astrophysics binary evolution models of CVs in which mass transfer begins just as the donor leaves the main sequence. These generically predict Na enhancement in donors with initial donor masses $\gtrsim 1\, {\rm M}_{\odot }$, consistent with our observations. In the models, Na enrichment occurs in the donors’ cores via the NeNa cycle near the end of their main-sequence evolution. Na-enhanced material is exposed when the binaries reach orbital periods of a few hours. Donors with higher initial masses are predicted to have higher Na abundances at fixed orbital period owing to their higher core temperatures during main-sequence evolution. The observed [Na/H] values are on average ≈0.3 dex higher than predicted by the models. Surface abundances of evolved CV donors provide a unique opportunity to study nuclear burning products in the cores of intermediate-mass stars.

Hidden Companions to Intermediate-mass Stars. VI. Discovery of a 0.50M ⊙, 6 au Companion to HIP 74696* *Based on observations collected at the European Southern Observatory, Chile, Program ID 111.24UP.001.

A-type stars with a large long-term proper motion change and without a known companion to cause it are candidates for being Sirius analogues. However, in most cases the culprit is expected to be a hitherto unknown low mass companion rather than a white dwarf. Here we report the discovery of a 0.50M ⊙ companion to the nearby 1.64M ⊙ star HIP 74696 at a projected separation ρ = 118.9 mas ↔ 6.2 au based on a VLTI/GRAVITY observation. This companion explains the Gaia–Hipparcos proper motion change of the primary. Together with the wide 660 au companion that was found by Gaia DR3 to be a 0.70M ⊙ + 0.20M ⊙ 1.5 au binary, this makes HIP 74696 a quadruple and part of the growing class of high multiplicity systems with an A-type star primary.