Programme ID Research Articles

Hidden Companions to Intermediate-mass Stars. Upgraded Multiplicity 2 → 3. XXIII. Discovery of a 0.94M ⊙, 9.2 au Companion to the Ap Star Gamma Piscis Austrini A* *Based on observations collected at the European Southern Observatory, Chile, Program ID 113.26GM.001.

Gamma Piscis Austrini is a nearby ρ = 4.″1 ↔ 284 au visual binary consisting of an A0Vp primary (A) and an F5V secondary (B). Here we report that the primary is actually a closer binary based on a VLTI/GRAVITY interferometric observation. The newly discovered companion Ab has a K band flux ratio 4.8% ± 0.2% and a projected separation ρ = 143.50 mas ↔ 9.2 au relative to Aa. We estimate isochrone masses M Aa = 2.65M ⊙, M Ab = 0.94M ⊙ and M B = 1.20M ⊙. γ PsA will become a triple white dwarf system within a Hubble time, with a low enough hierarchy for possibly interesting dynamical effects with a timescale P KL ∼ 200 kyr.

HATS-38 b and WASP-139 b Join a Growing Group of Hot Neptunes on Polar Orbits* * Based on observations made with the ESO telescopes at the La Silla Paranal Observatory under program ID 111.24VT.001, 111.24VT.002, and 112.25W1.001.

We constrain the sky-projected obliquities of two low-density hot Neptune planets, HATS-38 b and WASP-139 b, orbiting nearby G and K stars using Rossiter–McLaughlin (RM) observations with VLT/ESPRESSO, yielding λ=−108−16+11 deg and −85.6−4.2+7.7 deg, respectively. To model the RM effect, we use a new publicly available code, ironman, which is capable of jointly fitting transit photometry, Keplerian radial velocities, and RM effects. WASP-139 b has a residual eccentricity e=0.103−0.041+0.050 while HATS-38 b has an eccentricity of e=0.112−0.070+0.072 , which is compatible with a circular orbit given our data. Using the obliquity constraints, we show that they join a growing group of hot and low-density Neptunes on polar orbits. We use long-term radial velocities to rule out companions with masses ∼0.3–50 M J within ∼10 au. We show that the orbital architectures of the two Neptunes can be explained with high-eccentricity migration from ≳2 au driven by an unseen distant companion. If HATS-38 b has no residual eccentricity, its polar and circular orbit can also be consistent with a primordial misalignment. Finally, we perform a hierarchical Bayesian modeling of the true obliquity distribution of Neptunes and find suggestive evidence for a higher preponderance of polar orbits for hot Neptunes compared to Jupiters. However, we note that the exact distribution is sensitive to the choice of priors, highlighting the need for additional obliquity measurements of Neptunes to robustly compare the hot Neptune obliquity distribution to that of Jupiters.

Hidden Companions to Intermediate-mass Stars. XXII. Inferring a 0.43M ⊙, 1.65 au Companion in the Astrometric Binary within the Triple System Lambda Muscae* *Based on observations collected at the European Southern Observatory, Chile, Program ID 111.24UP.001.

Lambda Muscae is a nearby A-type star reported as a P = 474 days astrometric binary in Gaia DR3 (and previously in Hipparcos) and which also has a 0.16M ⊙ M dwarf companion at a projected separation 6.4 au discovered by VLT/SPHERE. Based on a K band flux ratio upper limit of 1% from a VLTI/GRAVITY interferometric observation, we estimate a primary mass M Aa = 2.28M ⊙ and infer that the closer companion is a M Ab = 0.43M ⊙ star (almost certainly an M dwarf) orbiting at a = 1.65 au. The triple system might be dynamically interesting given the low hierarchy and the ratio of angular momenta of the inner and outer orbits of about one.

Hidden Companions to Intermediate-mass Stars. XX. Discovery of a 0.58M ⊙, 7.4 au Companion to p Puppis* *Based on observations collected at the European Southern Observatory, Chile, Program ID 112.25QQ.001.

p Puppis is a nearby 3.1M ⊙ B8V star with astrometric evidence for a close companion in addition to its two wide companions at 1.3 kau (a white dwarf (WD)) and 38.7 kau (an F2V astrometric binary). Here we report on a VLTI/GRAVITY observation that revealed the close companion to be a 0.58M ⊙ star at a projected separation ρ = 100.2 mas ↔ 7.4 au, confirming the system to be a quintuple. The discovered companion explains the X-ray emission of p Pup detected by eROSITA. Moreover, we also find that the isochrone age of 100−20+50 Myr of p Pup is incompatible with the minimum cooling age of 350 Myr for the 1.3 kau wide WD companion, suggesting that either they are not coeval or that the WD was formed through a non-trivial channel.

On the Pair-instability Supernova Origin of J1010+2358* * Based on observations made with the Very Large Telescope (VLT) of the ESO at the La Silla Paranal Observatory under the program ID 112.26WJ.001

The first (Population III) stars formed only out of H and He and were likely more massive than present-day stars. Massive Population III stars in the range 140–260 M ⊙ are predicted to end their lives as pair-instability supernovae (PISNe), enriching the environment with a unique abundance pattern, with high ratios of odd to even elements. Recently, the most promising candidate for a pure descendant of a zero-metallicity massive PISN (260 M ⊙) was discovered by the LAMOST survey, the star J1010+2358. However, key elements to verify the high PISN contribution, C and Al, were missing from the analysis. To rectify this, we obtained and analyzed a high-resolution Very Large Telescope/UVES spectrum, correcting for 3D and/or non-local thermodynamic equilibrium effects. Our measurements of both C and Al give much higher values (∼1 dex) than expected from a 260 M ⊙ PISN. Furthermore, we find significant discrepancies with the previous analysis and therefore a much less pronounced odd–even pattern. Our results show that J1010+2358 cannot be a pure descendant of a 260 M ⊙ PISN. Instead, we find that the best-fit model consists of a 13 M ⊙ Population II core-collapse supernova combined with a Population III supernova. Alternative, less favored solutions ( χ2/χbest2≈2.3 ) include a 50% contribution from a 260 M ⊙ PISN or a 40% contribution from a Population III Type Ia supernova. Ultimately, J1010+2358 is certainly a unique star giving insights into the earliest chemical enrichment; however, this star is not a pure PISN descendant.

Hidden Companions to Intermediate-mass Stars. XIX. Spin–Orbit Misalignment and a 0.26M ⊙, 1.8 au Companion in the Astrometric Binary Gamma Trianguli Australis* *Based on observations collected at the European Southern Observatory, Chile, Program ID 111.24UP.001.

Gamma Trianguli Australis is a nearby A-type star that was reported to be a 488 days astrometric binary in Gaia DR3. Here we report on a VLTI/GRAVITY observation of γ TrA in which we did not detect the companion down to a K band flux ratio of 0.5%. From the isochrone mass M A = 3.04M ⊙ of the subgiant primary, this implies a semimajor axis a orb = 1.8 au and that the companion is a M B = 0.26M ⊙ M dwarf. The primary disk is partially resolved with an angular diameter θ 1 ≈ 1 mas ↔ 13.0R ⊙. The differential visibility phases across the Brγ absorption line allowed us to measure the longitude of the ascending node of the primary’s rotational plane Ωrot = 212° ± 3°. This implies a spin–orbit misalignment of at least 27° ± 3° based on the Gaia astrometric solution.

Hidden Companions to Intermediate-mass Stars. XVIII. Discovery of a 0.88M ⊙, 26 au Companion to n Centauri* *Based on observations collected at the European Southern Observatory, Chile, Program ID 111.24UP.001.

n Centauri is a nearby A-type star. Here we report the discovery of a companion with an H band flux ratio fBfA=3.9%±0.4% at a projected separation ρ = 570 mas ↔ 26 au based on the acquisition camera image of a VLTI/GRAVITY observation. Isochrone fitting yields masses M A = 2.07M ⊙ and M B = 0.88M ⊙ and an age of 900 Myr. The newly discovered companion explains the Δv = 2.3 ± 0.1 km s−1 Gaia-Hipparcos proper motion change of n Cen in both direction and magnitude as well as its X-ray emission. The interferometric data excludes the presence of any additional companion to the primary with a K band flux ratio higher than 0.9% (M ≳ 0.52M ⊙ for a main sequence star) within ρ > 5 mas ↔ 0.23 au.

Hidden Companions to Intermediate-mass Stars. XVII. Uncovering a 0.72 M ⊙, 0.35 au Companion in the Spectroscopic Binary Sigma Sculptoris* *Based on observations collected at the European Southern Observatory, Chile, Program ID 109.23BV.001.

Sigma Sculptoris is a nearby star that was suspected of being a rotating Ap variable. It was recently found not to be an Ap star but rather a 47 days single-lined spectroscopic binary. Here we report on the direct detection of the companion with a K band flux ratio of 5.5% at a projected separation of 5.16 mas based on a VLTI/GRAVITY observation. We estimate isochrone masses M A = 1.95M ⊙ and M B = 0.72M ⊙, a semimajor axis a = 0.35 au and an orbital inclination i = 27° (or 153°). The large rotational velocity of the primary (assuming spin–orbit alignment) is consistent with the lack of prominent chemical peculiarities.

JWST/NIRCam Imaging of Young Stellar Objects. III. Detailed Imaging of the Nebular Environment around the HL Tau Disk

As part of the James Webb Space Telescope (JWST) Guaranteed Time Observation program “Direct Imaging of YSOs” (program ID 1179), we use JWST NIRCam’s direct imaging mode in F187N, F200W, F405N, and F410M to perform high-contrast observations of the circumstellar structures surrounding the protostar HL Tau. The data reveal the known stellar envelope, outflow cavity, and streamers, but do not detect any companion candidates. We detect scattered light from an inflowing spiral streamer previously detected in HCO+ by the Atacama Large Millimeter/submillimeter Array, and part of the structure connected to the c-shaped outflow cavity. For detection limits in planet mass we use BEX evolutionary tracks when M p < 2 M J and AMES-COND evolutionary tracks otherwise, assuming a planet age of 1 Myr (youngest available age). Inside the disk region, due to extended envelope emission, our point-source sensitivities are ∼5 mJy (37 M J) at 40 au in F187N and ∼0.37 mJy (5.2 M J) at 140 au in F405N. Outside the disk region, the deepest limits we can reach are ∼0.01 mJy (0.75 M J) at a projected separation ∼ 525 au.

Hidden Companions to Intermediate-mass Stars. XV. Discovery of a 1.2M ⊙, 8.4 au Companion to the δ Scuti star HIP 41375 = 2 Hydrae* *Based on observations collected at the European Southern Observatory, Chile, Program ID 110.241W.001.

2 Hydrae is a nearby M Aa = 1.66M ⊙ δ Scuti star with strong astrometric evidence for a close companion in addition to its known M B = 0.20M ⊙ M dwarf companion at 530 au. Here we report on a VLTI/GRAVITY near-infrared interferometric observation that reveals the close companion to be a M Ab = 1.18M ⊙ star at a projected separation ρ = 168 mas ↔ 8.4 au. This triple system is a potential progenitor for a double white dwarf binary under the dynamical influence of an outer M dwarf companion with a low enough hierarchy for potentially interesting dynamical effects.

Early Results from GLASS-JWST. XXIV. The Mass–Metallicity Relation in Lensed Field Galaxies at Cosmic Noon with NIRISS* *Based on observations acquired by JWST under the ERS program ID 1324 (PI: T. Treu).

We present a measurement of the mass–metallicity relation (MZR) at Cosmic Noon, using the JWST near-infrared wide-field slitless spectroscopy obtained by the GLASS-JWST Early Release Science program. By combining the power of JWST and the lensing magnification by the foreground cluster A2744, we extend the measurements of the MZR to the dwarf mass regime at high redshifts. A sample of 50 galaxies with several emission lines is identified across two wide redshift ranges of z = 1.8–2.3 and 2.6–3.4 in the stellar mass range of log(M*/M⊙)∈[6.9,10.0] . The observed slope of MZR is 0.223 ± 0.017 and 0.294 ± 0.010 at these two redshift ranges, respectively, consistent with the slopes measured in field galaxies with higher masses. In addition, we assess the impact of the morphological broadening on emission line measurement by comparing two methods of using 2D forward modeling and line profile fitting to 1D extracted spectra. We show that ignoring the morphological broadening effect when deriving line fluxes from grism spectra results in a systematic reduction of flux by ∼30% on average. This discrepancy appears to affect all the lines and thus does not lead to significant changes in flux ratio and metallicity measurements. This assessment of the morphological broadening effect using JWST data presents, for the first time, an important guideline for future work deriving galaxy line fluxes from wide-field slitless spectroscopy, such as Euclid, Roman, and the Chinese Space Station Telescope.

The Aligned Orbit of the Eccentric Proto Hot Jupiter TOI-3362b* *Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program ID 110.23Y8.004.

High-eccentricity tidal migration predicts the existence of highly eccentric proto hot Jupiters on the “tidal circularization track,” meaning that they might eventually become hot Jupiters, but that their migratory journey remains incomplete. Having experienced moderate amounts of tidal evolution of their orbital elements, proto hot Jupiter systems can be powerful test beds for the underlying mechanisms of eccentricity growth. Notably, they may be used for discriminating between variants of high-eccentricity migration, each predicting a distinct evolution of misalignment between the star and the planet’s orbit. We constrain the spin–orbit misalignment of the proto hot Jupiter TOI-3362b with high-precision radial-velocity observations using ESPRESSO at Very Large Telescope. The observations reveal a sky-projected obliquity ° and constrain the orbital eccentricity to e = 0.720 ± 0.016, making it one of the most eccentric gas giants for which the obliquity has been measured. Although the large eccentricity and the striking orbit alignment of the planet are puzzling, we suggest that ongoing coplanar high-eccentricity migration driven by a distant companion is a possible explanation for the system's architecture. This distant companion would need to reside beyond 5 au at 95% confidence to be compatible with the available radial-velocity observations.

Hidden Companions to Intermediate-mass Stars. XIV. Discovery of a 1.8 M ⊙, 0.3 au Companion to Ascella = Zeta Sagittarii A* *Based on observations collected at the European Southern Observatory, Chile, Program ID 111.24UP.001.

Zeta Sagittarii is a nearby intermediate mass 13.2 au visual binary. Here we report on a VLTI/GRAVITY interferometric observation that revealed that ζ Sgr is actually a rather compact triple system: the visual primary Ascella (A) is a close equal mass ρ = 10.9 mas ↔ 0.3 au binary. Through isochrone fitting we find masses M Aa = 1.83M ⊙, M Ab = 1.81M ⊙ and M B = 2.03M ⊙. The hierarchy of the triple is low enough to allow for possibly interesting dynamical effects and its ultimate outcome will be a double or triple white dwarf system. We estimate that about 1 Myr ago ζ Sgr passed within a minimum distance of the Sun of 11 pc, rather than 3 pc as previously reported.

Hidden Companions to Intermediate-mass Stars. XIII. Discovery of a 0.80 M ⊙, 4.3 au Companion to HIP 7298* *Based on observations collected at the European Southern Observatory, Chile, Program ID 111.24UP.001.

Proper motion changes between astrometric surveys provide a hint for unresolved companions and near-infrared interferometry is arguably the most efficient way to reveal or constrain their nature. Here we report on the VLTI/GRAVITY. detection of a companion to the nearby star HIP 7298 with a K band flux ratio of 11.9% at a projected separation ρ = 57.1 mas ↔ 4.3 au. Through isochrone fitting we find that the primary is a 1 Gyr old M A = 1.56M ⊙ star while the newly discovered secondary is a M B = 0.80M ⊙ K dwarf. The stars will most likely avoid common envelope evolution and will become a system similar to Gliese 86 in about 1.5 Gyr.

Hidden Companions to Intermediate-mass Stars. XII. Discovery of a 1.8 M ⊙, 1.3 au Companion to Delta Serpentis A* *Based on observations collected at the European Southern Observatory, Chile, Program ID 60.A-9801(U).

Delta Serpentis is a nearby 4″ visual binary (A+B) that has accrued a number of astrometric anomalies. Here we show that the primary component is actually a close binary based on a VLTI/GRAVITY archival interferometric observation. The newly discovered companion has a K band flux ratio of 33% at a projected separation ρ = 23.9 mas ↔ 1.3 au. Through isochrone fitting we find somewhat evolved 1.2 Gyr old M Aa = 1.98 M ⊙, M Ab = 1.80 M ⊙ and M B = 1.88 M ⊙ stars. Delta Ser joins a growing list of intermediate mass hierarchical multiples and may be a progenitor of a rather rare system of three white dwarfs.

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.

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.

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.

Hidden Companions to Intermediate-mass Stars. V. Discovery of a 1.6 M ⊙, 0.3 au Companion to Marfik within the 48 au Visual Binary HIP 80883 = λ Ophiuchi* *Based on observations collected at the European Southern Observatory, Chile, Program ID 111.24UP.003.

λ Ophiuchi is a nearby 48 au intermediate-mass visual binary with a hierarchical, 6400 au wide companion. We report on the discovery of a close companion to the primary star (Marfik) with a K band flux ratio of 33% at a projected separation ρ = 6.1 mas ↔ 0.32 au based on a VLTI/GRAVITY observation. Isochrone fitting yields masses M Aa = 2.39M ⊙, M Ab = 1.62M ⊙ and M B = 1.82M ⊙. λ Oph therefore joins a growing number of intermediate-mass binaries with 10–60 au separation in which the primary is found to be a close binary and which suggest that many white dwarfs with a main sequence companion at such separations (such as Sirius B) ultimately descended from merger products. In fact, λ Oph is a potential progenitor for a system resembling Sirius.