Comparable Mass Research Articles

OGLE-2013-BLG-0911Lb: A Secondary on the Brown-dwarf Planet Boundary around an M Dwarf

Abstract We present the analysis of the binary-lens microlensing event OGLE-2013-BLG-0911. The best-fit solutions indicate the binary mass ratio of q ≃ 0.03, which differs from that reported in Shvartzvald et al. The event suffers from the well-known close/wide degeneracy, resulting in two groups of solutions for the projected separation normalized by the Einstein radius of s ∼ 0.15 or s ∼ 7. The finite source and the parallax observations allow us to measure the lens physical parameters. The lens system is an M dwarf orbited by a massive Jupiter companion at very close ( M host = 0.30 − 0.06 + 0.08 M ⊙ , M comp = 10.1 − 2.2 + 2.9 M Jup , a exp = 0.40 − 0.04 + 0.05 au ) or wide ( M host = 0.28 − 0.08 + 0.10 M ⊙ , M comp = 9.9 − 3.5 + 3.8 M Jup , a exp = 18.0 − 3.2 + 3.2 au ) separation. Although the mass ratio is slightly above the planet-brown dwarf (BD) mass-ratio boundary of q = 0.03, which is generally used, the median physical mass of the companion is slightly below the planet-BD mass boundary of 13M Jup. It is likely that the formation mechanisms for BDs and planets are different and the objects near the boundaries could have been formed by either mechanism. It is important to probe the distribution of such companions with masses of ∼13M Jup in order to statistically constrain the formation theories for both BDs and massive planets. In particular, the microlensing method is able to probe the distribution around low-mass M dwarfs and even BDs, which is challenging for other exoplanet detection methods.

Population-level Eccentricity Distributions of Imaged Exoplanets and Brown Dwarf Companions: Dynamical Evidence for Distinct Formation Channels*

Abstract The orbital eccentricities of directly imaged exoplanets and brown dwarf companions provide clues about their formation and dynamical histories. We combine new high-contrast imaging observations of substellar companions obtained primarily with Keck/NIRC2 together with astrometry from the literature to test for differences in the population-level eccentricity distributions of 27 long-period giant planets and brown dwarf companions between 5 and 100 au using hierarchical Bayesian modeling. Orbit fits are performed in a uniform manner for companions with short orbital arcs; this typically results in broad constraints for individual eccentricity distributions, but together as an ensemble, these systems provide valuable insight into their collective underlying orbital patterns. The shape of the eccentricity distribution function for our full sample of substellar companions is approximately flat from e = 0–1. When subdivided by companion mass and mass ratio, the underlying distributions for giant planets and brown dwarfs show significant differences. Low mass ratio companions preferentially have low eccentricities, similar to the orbital properties of warm Jupiters found with radial velocities and transits. We interpret this as evidence for in situ formation on largely undisturbed orbits within massive extended disks. Brown dwarf companions exhibit a broad peak at e ≈ 0.6–0.9 with evidence for a dependence on orbital period. This closely resembles the orbital properties and period-eccentricity trends of wide (1–200 au) stellar binaries, suggesting that brown dwarfs in this separation range predominantly form in a similar fashion. We also report evidence that the “eccentricity dichotomy” observed at small separations extends to planets on wide orbits: the mean eccentricity for the multi-planet system HR 8799 is lower than for systems with single planets. In the future, larger samples and continued astrometric orbit monitoring will help establish whether these eccentricity distributions correlate with other parameters such as stellar host mass, multiplicity, and age.

A search for pulsars in subdwarf B binary systems and discovery of giant-pulse emitting PSR J0533−4524

ABSTRACT Binary millisecond pulsars (MSPs) provide several opportunities for research of fundamental physics. However, finding them can be challenging. Several subdwarf B (sdB) binary systems with possible neutron star companions have been identified, allowing us to perform a targeted search for MSPs within these systems. Six sdBs with companions in the neutron star mass range, as determined from their optical light curves, were observed with the Green Bank and Westerbork radio telescopes. The data were searched for periodic signals as well as single pulses. No radio pulsations from sdB systems were detected, down to an average sensitivity limit of $0.11\,$mJy. We did, however, discover a pulsar in the field of sdB HE0532−4503. Follow-up observations with the Giant Metrewave Radio Telescope showed that this pulsar, J0533−4524, is not spatially coincident with the sdB system. The pulsar has a relatively low magnetic field but still emits giant pulses. We place an upper limit of three to the number of radio pulsars in the six sdB systems. The non-detections may be explained by a combination of the MSP beaming fraction, luminosity, and a recycling fraction <0.5. Alternatively, the assumption of corotation between the MSP and sdB may break down, which implies the systems are more edge-on than previously thought. This would shift the predicted companion masses into the white dwarf range. It would also explain the relative lack of edge-on sdB systems with massive companions.

XO-7 b: A Transiting Hot Jupiter with a Massive Companion on a Wide Orbit

Abstract Transiting planets orbiting bright stars are the most favorable targets for follow-up and characterization. We report the discovery of the transiting hot Jupiter XO-7 b and of a second, massive companion on a wide orbit around a circumpolar, bright, and metal-rich G0 dwarf (V = 10.52, , ). We conducted photometric and radial velocity follow-up with a team of amateur and professional astronomers. XO-7 b has a period of days, a mass of , a radius of , a density of , and an equilibrium temperature of . Its large atmospheric scale height and the brightness of the host star make it well suited to atmospheric characterization. The wide-orbit companion is detected as a linear trend in radial velocities with an amplitude of over two years, yielding a minimum mass of 4 ; it could be a planet, a brown dwarf, or a low-mass star. The hot Jupiter orbital parameters and the presence of the wide-orbit companion point toward a high-eccentricity migration for the hot Jupiter. Overall, this system will be valuable to understand the atmospheric properties and migration mechanisms of hot Jupiters and will help constrain the formation and evolution models of gas giant exoplanets.

Not so fast: LB-1 is unlikely to contain a 70 M⊙ black hole

ABSTRACT The recently discovered binary LB-1 has been reported to contain a ${\sim }70\, \mathrm{M}_{\odot}$ black hole (BH). The evidence for the unprecedentedly high mass of the unseen companion comes from reported radial velocity (RV) variability of the H α emission line, which has been proposed to originate from an accretion disc around a BH. We show that there is in fact no evidence for RV variability of the H α emission line, and that its apparent shifts instead originate from shifts in the luminous star’s H α absorption line. If not accounted for, such shifts will cause a stationary emission line to appear to shift in antiphase with the luminous star. We show that once the template spectrum of a B star is subtracted from the observed Keck/HIRES spectra of LB-1, evidence for RV variability vanishes. Indeed, the data rule out periodic variability of the line with velocity semi-amplitude $K_{\rm H\,\alpha } \gt 1.3\, {\rm {km}} \, s^{-1}$. This strongly suggests that the observed H α emission does not originate primarily from an accretion disc around a BH, and thus that the mass ratio cannot be constrained from the relative velocity amplitudes of the emission and absorption lines. The nature of the unseen companion remains uncertain, but a ‘normal’ stellar-mass BH with mass 5 ≲ M/M⊙ ≲ 20 seems most plausible. The H α emission likely originates primarily from circumbinary material, not from either component of the binary.

Measuring the Mass of the Faint Companion to FW Tau with ALMA

Measuring the Mass of the Faint Companion to FW Tau with ALMA

ALMA and NACO observations towards the young exoring transit system J1407 (V1400 Cen)

Aims. Our aim was to directly detect the thermal emission of the putative exoring system responsible for the complex deep transits observed in the light curve for the young Sco-Cen star 1SWASP J140747.93-394542.6 (V1400 Cen, hereafter J1407), confirming it as the occulter seen in May 2007, and to determine its orbital parameters with respect to the star. Methods. We used the Atacama Large Millimeter/submillimeter Array (ALMA) to observe the field centred on J1407 in the 340 GHz (Band 7) continuum in order to determine the flux and astrometric location of the ring system relative to the star. We used the VLT/NACO camera to observe the J1407 system in March 2019 and to search for the central planetary mass object at thermal infrared wavelengths. Results. We detect no point source at the expected location of J1407, and derive an upper limit 3σ level of 57.6 μJy. There is a point source detected at an angular separation consistent with the expected location for a free-floating ring system that occulted J1407 in May 2007, with a flux of 89 μJy consistent with optically thin dust surrounding a massive substellar companion. At 3.8 μm with the NACO camera, we detect the star J1407 but no other additional point sources within 1.3 arcsec of the star, with a lower bound on the sensitivity of 6 MJup at the location of the ALMA source, and down to 4 MJup in the sky background limit. Conclusions. The ALMA upper limit at the location of J1407 implies that a hypothesised bound ring system is composed of dust smaller than 1 mm in size, implying a young ring structure. The detected ALMA source has multiple interpretations, including: (i) it is an unbound substellar object surrounded by warm dust in Sco-Cen with an upper mass limit of 6 MJup, or (ii) it is a background galaxy.

A stripped helium star in the potential black hole binary LB-1

Context. The recently claimed discovery of a massive (MBH = 68−13+11 M⊙) black hole in the Galactic solar neighborhood has led to controversial discussions because it severely challenges our current view of stellar evolution. Aims. A crucial aspect for the determination of the mass of the unseen black hole is the precise nature of its visible companion, the B-type star LS V+22 25. Because stars of different mass can exhibit B-type spectra during the course of their evolution, it is essential to obtain a comprehensive picture of the star to unravel its nature and, thus, its mass. Methods. To this end, we study the spectral energy distribution of LS V+22 25 and perform a quantitative spectroscopic analysis that includes the determination of chemical abundances for He, C, N, O, Ne, Mg, Al, Si, S, Ar, and Fe. Results. Our analysis clearly shows that LS V+22 25 is not an ordinary main sequence B-type star. The derived abundance pattern exhibits heavy imprints of the CNO bi-cycle of hydrogen burning, that is, He and N are strongly enriched at the expense of C and O. Moreover, the elements Mg, Al, Si, S, Ar, and Fe are systematically underabundant when compared to normal main-sequence B-type stars. We suggest that LS V+22 25 is a stripped helium star and discuss two possible formation scenarios. Combining our photometric and spectroscopic results with the Gaia parallax, we infer a stellar mass of 1.1 ± 0.5 M⊙. Based on the binary system’s mass function, this yields a minimum mass of 2–3 M⊙ for the compact companion, which implies that it may not necessarily be a black hole but a massive neutron- or main sequence star. Conclusions. The star LS V+22 25 has become famous for possibly having a very massive black hole companion. However, a closer look reveals that the star itself is a very intriguing object. Further investigations are necessary for complete characterization of this object.

A Hidden Friend for the Galactic Center Black Hole, Sgr A*

Abstract The hierarchical nature of galaxy formation suggests that a supermassive black hole binary could exist in our galactic center. We propose a new approach to constraining the possible orbital configuration of such a binary companion to the galactic center black hole Sagittarius A* (Sgr A*) through the measurement of stellar orbits. Focusing on the star S0–2, we show that requiring its orbital stability in the presence of a companion to Sgr A* yields stringent constraints on the possible configurations of such a companion. Furthermore, we show that precise measurements of time variations in the orbital parameters of S0–2 could yield stronger constraints. Using existing data on S0–2 we derive upper limits on the binary black hole separation as a function of the companion mass. For the case of a circular orbit, we can rule out a 105 M ⊙ companion with a semimajor axis greater than 170 au or 0.8 mpc. This is already more stringent than bounds obtained from studies of the proper motion of Sgr A*. Including other stars orbiting the galactic center should yield stronger constraints that could help uncover the presence of a companion to Sgr A*. We show that a companion can also affect the accretion process, resulting in a variability that may be consistent with the measured infrared flaring timescales and amplitudes. Finally, if such a companion exists, it will emit gravitational wave radiation, potentially detectable with the Laser Interferometer Space Antenna (LISA).

Formation and Merging of Mass Gap Black Holes in Gravitational-wave Merger Events from Wide Hierarchical Quadruple Systems

Abstract We investigate secular evolution in hierarchical quadruple systems as a formation channel of mass-gap black holes (with masses of about 3–5M ⊙) in systems that will eventually lead to binary black hole mergers detectable by ground-based gravitational-wave detectors (LIGO/Virgo). We show that in a 3 + 1 hierarchical system, two episodes of induced mergers would first cause two neutron stars to merge and form a mass-gap black hole, which will subsequently merge with another (more massive) black hole through a second induced merger. We demonstrate that such systems are stable to flybys, and their formation would predict a high mass ratio and eccentric merger of a mass-gap black hole with a more massive black hole companion. Such a formation channel may explain observed gravitational-wave events such as the recently discovered LIGO/Virgo events S190814bv and S190924h.

A diagnostic of the orbital spectrum of LS 5039 with Fermi-LAT

LS 5039 is a well-known γ-ray binary system which consists of an unknown compact object and a massive companion O star. It shows rather stable emissions at high energies over years and hence serves as an ideal laboratory to investigate the emission mechanism for such peculiar systems which emit prominent γ-rays. To this end, we take the orbital phase resolved energy spectrum as observed by Fermi-LAT over 10 years. We divide the orbit into four orbital phases, each with an orbital phase range of 0.25, centered at 0.00, 0.25, 0.50 and 0.75 respectively, where the phase 0.0 is the periastron and phase 0.5 is the apastron. The phases around 0.25 and 0.75 are symmetric and hence are supposed to have identical local acceleration environment. The spectral analysis shows that the Fermi-LAT spectra are largely different from these two symmetric orbital phases: the emission from orbital phase 0.25 turns out to be significantly stronger than that from 0.75. This result does not fit a scenario that γ-rays are Doppler boosted emission from bow shock tails if LS 5039 has a shock configuration similar to PSR B1259-63, and indicates that the inverse Compton scatterings between the shock accelerated plasma and the stellar particle environment is the underline procedure. We also find that the previous report for a disappearance of the orbital modulation at 3–20 GeV is due to the similar spectral turn-over energies of the different orbital phases. The spectral properties of periastron and apastron regions are addressed in the context of the measurements in phase regions around 0.25 and 0.75.

Super-Earth ingestion can explain the anomalously high metal abundances of M67 Y2235

Abstract We investigate the hypothesis that ingestion of a terrestrial or super-Earth planet could cause the anomalously high metal abundances seen in a turn-off star in the open cluster M67, when compared to other turn-off stars in the same cluster. We show that the mass of the convective envelope of the star is likely only 3.45 × 10−3 M⊙, and hence 5.2 M⊕ of rock is required to obtain the observed 0.128 dex metal enhancement. Rocky planets dissolve entirely in the convective envelope if they enter it with sufficiently tangential orbits: we find that the critical condition for dissolution is that the planet’s radial velocity must be less than 40% of its total velocity at the stellar surface; or, equivalently, the impact parameter must be greater than about 0.9. We model the delivery of rocky planets to the stellar surface both by planet-planet scattering in a realistic multi-planet system, and by Lidov–Kozai cycles driven by a more massive planetary or stellar companion. In both cases almost all planets that are ingested arrive at the star on grazing orbits and hence will dissolve in the surface convection zone. We conclude that super-Earth ingestion is a good explanation for the metal enhancement in M67 Y2235, and that a high-resolution spectroscopic survey of stellar abundances around the turn-off and main sequence of M67 has the potential to constrain the frequency of late-time dynamical instability in planetary systems.

The Possible Astrometric Signature of a Planetary-mass Companion to the Nearby Young Star TW Piscis Austrini (Fomalhaut B): Constraints from Astrometry, Radial Velocities, and Direct Imaging

Abstract We present constraints on the presence of substellar companions to the nearby (d ∼ 7.6 pc) young (440 ± 40 Myr) K4Ve star TW Piscis Austrini, the wide (∼0.3 pc) companion to the A4V star Fomalhaut. We combined absolute astrometry from Hipparcos and Gaia with literature radial velocity measurements and dedicated high-contrast imaging observations obtained with Keck/NIRC2 to achieve sensitivity to brown dwarf and planetary-mass companions (≳2 M Jup) over many decades of orbital period (≲103 yr). The significant astrometric acceleration measured between the Hipparcos and Gaia catalogs, reported previously in the literature, cannot be explained by the orbital motion of TW PsA around the barycenter of the Fomalhaut triple system. Instead, we find that it is consistent with the reflex motion induced by an orbiting substellar companion. The combination of astrometry, radial velocities, and a deep L′ imaging data set leads to a constraint on the companion mass of M Jup. However, the period of the companion is poorly constrained, with a highly multimodal period posterior distribution due to aliasing with the 24.25 yr baseline between Hipparcos and Gaia. If confirmed through continued astrometric or spectroscopic monitoring or via direct detection, the companion to TW PsA would represent a choice target for detailed atmospheric characterization with high-contrast instruments on the upcoming James Webb Space Telescope and Wide Field Infrared Survey Telescope.

Detection and characterisation of 54 massive companions with the SOPHIE spectrograph

Context. Brown dwarfs (BD) are substellar objects intermediate between planets and stars with masses of ~13–80 MJ. While isolated BDs are most likely produced by gravitational collapse in molecular clouds down to masses of a few MJ, a non-negligible fraction of low-mass companions might be formed through the planet-formation channel in protoplanetary discs. The upper mass limit of objects formed within discs is still observationally unknown, the main reason being the strong dearth of BD companions at orbital periods shorter than 10 yr, also known as the BD desert. Aims. To address this question, we aim at determining the best statistics of companions within the 10–100 MJ mass regime and located closer than ~10 au to the primary star, while minimising observation and selection bias. Methods. We made extensive use of the radial velocity (RV) surveys of northern hemisphere FGK stars within 60 pc of the Sun, performed with the SOPHIE spectrograph at the Observatoire de Haute-Provence. We derived the Keplerian solutions of the RV variations of 54 sources. Public astrometric data of the HIPPARCOS and Gaia missions allowed us to constrain the masses of the companions for most sources. We introduce GASTON, a new method to derive inclination combining RVs and Keplerian and astrometric excess noise from Gaia DR1. Results. We report the discovery of 12 new BD candidates. For five of them, additional astrometric data led to a revision of their mass in the M-dwarf regime. Among the seven remaining objects, four are confirmed BD companions, and three others are likely also in this mass regime. Moreover, we report the detection of 42 M-dwarfs within the range of 90 MJ–0.52 M⊙. The resulting M sin i-P distribution of BD candidates shows a clear drop in the detection rate below 80-day orbital period. Above that limit, the BD desert appears rather wet, with a uniform distribution of the M sin i. We derive a minimum BD-detection frequency around Solar-like stars of 2.0 ± 0.5%.

Detection of the PSR J1741+1351 white dwarf companion with the Gran Telescopio Canarias

We report detection of the binary companion to the millisecond pulsar J1741+1351 with the Gran Telescopio Canarias. The optical source position coincides with the pulsar coordinates and its magnitudes are g′ = 24.84(5), r′ = 24.38(4) and i′ = 24.17(4). Comparison of the data with the WD evolutionary models shows that the source can be a He-core WD with a temperature of ≈ 6000 K and a mass of ≈ 0.2M⊙. The latter is in excellent agreement with the companion mass obtained from the radio timing solution for PSR J1741+1351.

Constraints on the Occurrence and Distribution of 1–20 MJup Companions to Stars at Separations of 5–5000 au from a Compilation of Direct Imaging Surveys

Abstract We present the first statistical analysis of exoplanet direct imaging surveys combining adaptive optics (AO) imaging at small separations with deep seeing-limited observations at large separations allowing us to study the entire orbital separation domain from 5 to 5000 au simultaneously. Our sample of 344 stars includes only confirmed members of nearby young associations and is based on all AO direct-imaging detection limits readily available online, with addition of our own previous seeing-limited surveys. Assuming that the companion distribution in mass and a semimajor axis follows a power-law distribution and adding a dependence on the mass of the host star, such as , we constrain the parameters to obtain , , and at a 68% confidence level, and we obtain for the overall planet occurrence rate for companions with masses between 1 and 20 in the range of 5–5000 au. Thus, we find that occurrence of companions is negatively correlated with a semimajor axis and companion mass (marginally) but is positively correlated with the stellar host mass. Our inferred mass distribution is in good agreement with other distributions found previously from direct imaging surveys for planets and brown dwarfs, but is shallower as a function of mass than the distributions inferred by radial velocity surveys of gas giants in the 1–3 au range. This may suggest that planets at these wide and very wide separations represent the low-mass tail of the brown dwarfs and stellar companion distribution rather than an extension of the distribution of the inner planets.

How drag force evolves in global common envelope simulations

ABSTRACT We compute the forces, torque, and rate of work on the companion-core binary due to drag in global simulations of common envelope (CE) evolution for three different companion masses. Our simulations help to delineate regimes when conventional analytic drag force approximations are applicable. During and just prior to the first periastron passage of the in-spiral phase, the drag force is reasonably approximated by conventional analytic theory and peaks at values proportional to the companion mass. Good agreement between global and local 3D ‘wind tunnel’ simulations, including similar net drag force and flow pattern, is obtained for comparable regions of parameter space. However, subsequent to the first periastron passage, the drag force is up to an order of magnitude smaller than theoretical predictions, quasi-steady, and depends only weakly on companion mass. The discrepancy is exacerbated for larger companion mass and when the inter-particle separation reduces to the Bondi–Hoyle–Lyttleton accretion radius, creating a turbulent thermalized region. Greater flow symmetry during this phase leads to near balance of opposing gravitational forces in front of and behind the companion, hence a small net drag. The reduced drag force at late times helps explain why companion-core separations necessary for envelope ejection are not reached by the end of limited duration CE simulations.

Upgraded Giant Metrewave Radio Telescope timing of NGC 1851A: a possible millisecond pulsar - neutron star system.

In this work, we present the results of 1 yr of upgraded Giant Metrewave Radio Telescope timing measurements of PSRJ0514-4002A, a 4.99-ms pulsar in a 18.8-d eccentric ([Formula: see text]) orbit with a massive companion located in the globular cluster NGC 1851. Combining these data with earlier Green Bank Telescope data, we greatly improve the precision of the rate of advance of periastron, [Formula: see text] which, assuming the validity of general relativity, results in a much refined measurement of the total mass of the binary, [Formula: see text]. Additionally, we measure the Einstein delay parameter, γ, something that has never been done for any binary system with an orbital period larger than [Formula: see text]10h. The measured value, [Formula: see text], is by far the largest for any binary pulsar. Furthermore, we measure the proper motion of the system ([Formula: see text] and [Formula: see text]), which is not only important for analysing its motion in the cluster, but is also essential for a proper interpretation of γ, given the latter parameter's correlation with the variation of the projected semimajor axis. The measurements of γ and the proper motion enable a separation of the system component masses: we obtain a pulsar mass of [Formula: see text] and a companion mass of [Formula: see text]. This raises the possibility that the companion is also a neutron star. Searches for radio pulsations from the companion have thus far been unsuccessful; hence, we cannot confirm the latter hypothesis. The low mass of this millisecond pulsar - one of the lowest ever measured for such objects - clearly indicates that the recycling process can be achieved with a relatively small amount of mass transfer.

Combining high-contrast imaging and radial velocities to constrain the planetary architectures of nearby stars

Context. Nearby stars are prime targets for exoplanet searches and characterization using a variety of detection techniques. Combining constraints from the complementary detection methods of high-contrast imaging (HCI) and radial velocity (RV) can further constrain the planetary architectures of these systems because these methods place limits at different regions of the companion mass and semi-major axis parameter space. Compiling a census of the planet population in the solar neighborhood is important to inform target lists for future space missions that will specifically target nearby stars to search for Earth analogs. Aims. We aim to constrain the planetary architectures from the combination of HCI and RV data for six nearby stars within 6 pc: τ Ceti, Kapteyn’s star, AX Mic, 40 Eri, HD 36395, and HD 42581. We explored where HCI adds information to constraints from the long-term RV monitoring data for these stars. Methods. We compiled the sample from stars with available archival VLT/NACO HCI data at L′ band (3.8 μm), where we expect substellar companions to be brighter for the typically older ages of nearby field stars (>1 Gyr). The NACO data were fully reanalyzed using the state-of-the-art direct imaging pipeline PynPoint and combined with RV data from HARPS, Keck/HIRES, and CORALIE. A Monte Carlo approach was used to assess the completeness in the companion mass and semi-major axis parameter space from the combination of the HCI and RV data sets. Results. We find that the HCI data add significant information to the RV constraints, increasing the completeness for certain companions masses and semi-major axes by up to 68–99% for four of the six stars in our sample, and by up to 1–13% for the remaining stars. The improvements are strongest for intermediate semi-major axes (15–40 AU), corresponding to the semi-major axes of the ice giants in our own solar system. The HCI mass limits reach 5–20 MJup in the background-limited regime, depending on the age of the star. Conclusions. Through the combination of HCI and RV data, we find that stringent constraints can be placed on the possible substellar companions in these systems. Applying these methods systematically to nearby stars will quantify our current knowledge of the planet population in the solar neighborhood and inform future observations.

Searching for Wide Companions and Identifying Circum(sub)stellar Disks through PSF Fitting of Spitzer/IRAC Archival Images

Abstract Direct imaging surveys have discovered wide-orbit planetary-mass companions that challenge existing models of both star and planet formation, but their demographics remain poorly sampled. We have developed an automated binary companion point-spread function (PSF) fitting pipeline to take advantage of Spitzer's infrared sensitivity to planetary-mass objects and circum(sub)stellar disks, measuring photometry across the four Infrared Array Camera (IRAC) channels of 3.6, 4.5, 5.8, and 8.0 μm. We present PSF fitting photometry of archival Spitzer/IRAC images for 11 young, low-mass (M ∼ 0.044–0.88 M ⊙; K3.5–M7.5) members of three nearby star-forming regions (Chameleon, Taurus, and Upper Scorpius; d ∼ 150 pc; τ ∼ 1–10 Myr) that host confirmed or candidate faint companions at ρ = 1.″68–7.″31. We recover all system primaries, six confirmed, and two candidate low-mass companions in our sample. We also measure nonphotospheric [3.6]–[8.0] colors for three of the system primaries, four of the confirmed companions, and one candidate companion, signifying the presence of circumstellar or circum(sub)stellar disks. We furthermore report the confirmation of a ρ = 4.″66 (540 au) companion to [SCH06] J0359+2009 which was previously identified as a candidate via imaging over five years ago, but was not studied further. Based on its brightness (M [3.6] = 8.53 mag), we infer the companion mass to be M = 20 ± 5 M Jup given the primary’s model-derived age of 10 Myr. Our framework is sensitive to companions with masses less than 10 M Jup at separations of ρ = 300 au in nearby star-forming regions, opening up a new regime of parameter space that has yet to be studied in detail, discovering planetary-mass companions in their birth environments and revealing their circum(sub)stellar disks.