arXiv subjects

M. Tamura

Publications and source records attributed to M. Tamura.

At least 73 records · Page 4Linked to original sources

arXiv2016

Polarimetry and flux distribution in the debris disk around HD 32297

We present high-contrast angular differential imaging (ADI) observations of the debris disk around HD 32297 in H-band, as well as the first polarimetric images for this system in polarized differential imaging (PDI) mode with Subaru/HICIAO. In ADI, we detect the nearly edge-on disk at >5sigma levels from ~0.45 arcsec to ~1.7 arcsec (50-192 AU) from the star and recover the spine deviation from the midplane already found in previous works. We also find for the first time imaging and surface brightness (SB) indications for the presence of a gapped structure on both sides of the disk at distances of ~0.75 arcsec (NE side) and ~0.65 arcsec (SW side). Global forward-modelling work delivers a best-fit model disk and well-fitting parameter intervals that essentially match previous results, with high-forward scattering grains and a ring located at 110 AU. However, this single ring model cannot account for the gapped structure seen in our SB profiles. We create simple double ring models and achieve a satisfactory fit with two rings located at 60 and 95 AU, respectively, low-forward scattering grains and very sharp inner slopes. In polarized light we retrieve the disk extending from ~0.25-1.6 arcsec, although the central region is quite noisy and high S/N are only found in the range ~0.75-1.2 arcsec. The disk is polarized in the azimuthal direction, as expected, and the departure from the midplane is also clearly observed. Evidence for a gapped scenario is not found in the PDI data. We obtain a linear polarization degree of the grains that increases from ~10% at 0.55 arcsec to ~25% at 1.6 arcsec. The maximum is found at scattering angles of ~90degrees, either from the main components of the disk or from dust grains blown out to larger radii.

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arXiv2016

Water ice at the surface of HD 100546 disk

We made near infrared multicolor imaging observations of a disk around Herbig Be star HD100546 using Gemini/NICI. K (2.2\,$μ$m), H$_2$O ice (3.06\,$μ$m), and L'(3.8\,$μ$m) disk images were obtained and we found the 3.1\,$μ$m absorption feature in the scattered light spectrum, likely due to water ice grains at the disk surface. We compared the observed depth of the ice absorption feature with the disk model based on \cite{Oka2012} including water ice photodesorption effect by stellar UV photons. The observed absorption depth can be explained by the both disk models with/without photodesorption effect within the measurement accuracy, but slightly favors the model with photodesorption effects, implying that the UV photons play an important role on the survival/destruction of ice grains at the Herbig Ae/Be disk surface. Further improvement on the accuracy of the observations of the water ice absorption depth is needed to constrain the disk models.

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arXiv2015

V899 Mon: An Outbursting Protostar With Peculiar Light Curve And Its Transition Phases

We present a detailed study of V899 Mon (a new member in the FUors/EXors family of young low-mass stars undergoing outburst), based on our long-term monitoring of the source starting from November 2009 to April 2015. Our optical and near-infrared photometric and spectroscopic monitoring recorded the source transitioning from its first outburst to a short duration quiescence phase ($<$ 1 year), and then returning to a second outburst. We report here the evolution of the outflows from inner region of the disk as the accretion rate evolved in various epochs. Our high resolution (R$\sim$37000) optical spectrum could resolve interesting clumpy structures in the outflow traced by various lines. Change in far-infrared flux was also detected between two outburst epochs. Based on our observations we constrained various stellar and envelope parameters of V899 Mon, as well as the kinematics of its accretion and outflow. The photometric and spectroscopic properties of this source fall between classical FUors and EXors. Our investigation of V899 Mon hints instability associated with magnetospheric accretion to be the physical cause of sudden short duration pause of outburst in 2011. It is also a good candidate to explain similar short duration pauses in outburst of some other FUors/EXors sources.

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arXiv2015

The Subaru Coronagraphic Extreme Adaptive Optics system: enabling high-contrast imaging on solar-system scales

The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument is a multipurpose high-contrast imaging platform designed for the discovery and detailed characterization of exoplanetary systems and serves as a testbed for high-contrast imaging technologies for ELTs. It is a multi-band instrument which makes use of light from 600 to 2500nm allowing for coronagraphic direct exoplanet imaging of the inner 3 lambda/D from the stellar host. Wavefront sensing and control are key to the operation of SCExAO. A partial correction of low-order modes is provided by Subaru's facility adaptive optics system with the final correction, including high-order modes, implemented downstream by a combination of a visible pyramid wavefront sensor and a 2000-element deformable mirror. The well corrected NIR (y-K bands) wavefronts can then be injected into any of the available coronagraphs, including but not limited to the phase induced amplitude apodization and the vector vortex coronagraphs, both of which offer an inner working angle as low as 1 lambda/D. Non-common path, low-order aberrations are sensed with a coronagraphic low-order wavefront sensor in the infrared (IR). Low noise, high frame rate, NIR detectors allow for active speckle nulling and coherent differential imaging, while the HAWAII 2RG detector in the HiCIAO imager and/or the CHARIS integral field spectrograph (from mid 2016) can take deeper exposures and/or perform angular, spectral and polarimetric differential imaging. Science in the visible is provided by two interferometric modules: VAMPIRES and FIRST, which enable sub-diffraction limited imaging in the visible region with polarimetric and spectroscopic capabilities respectively. We describe the instrument in detail and present preliminary results both on-sky and in the laboratory.

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arXiv2015

Star formation in the filament of S254-S258 OB complex: a cluster in the process of making

Infrared Dark Clouds are ideal laboratories to study the initial processes of high-mass star and star cluster formation. We investigated star formation activity of an unexplored filamentary dark cloud (~5.7pc x 1.9pc), which itself is part of a large filament (~20pc) located in the S254-S258 OB complex at a distance of 2.5kpc. Using MIPS Spitzer 24 micron data, we uncover 49 sources with SNR greater than 5. We identified 45 sources as candidate YSOs of Class I, Flat-spectrum & Class II nature. Additional 17 candidate YSOs (9 Class I & 8 Class II) are also identified using JHK and WISE photometry. We find that the protostar to Class II sources ratio (~2) and the protostar fraction (~70%) of the region are high. When the protostar fraction compared to other young clusters, it suggests that the star formation in the dark cloud was possibly started only 1 Myr ago. Combining the NIR photometry of the YSO candidates with the theoretical evolutionary models, we infer that most of the candidate YSOs formed in the dark cloud are low-mass (<2 Msolar) in nature. We examine the spatial distribution of the YSOs and find that majority of them are linearly aligned along the highest column density line (N(H2) ~1 x 10^22 cm^-2) of the dark cloud along its long axis at mean nearest neighbor separation of ~0.2pc. Using observed properties of the YSOs, physical conditions of the cloud and a simple cylindrical model, we explore the possible star formation process of this filamentary dark cloud and suggest that gravitational fragmentation within the filament should have played a dominant role in the formation of the YSOs. From the total mass of the YSOs, gaseous mass associated with the dark cloud, and surrounding environment, we infer that the region is presently forming stars at an efficiency ~3% and a rate ~30 Msolar Myr^-1, and may emerge to a richer cluster.

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arXiv2015

Discovery of a Disk Gap Candidate at 20 AU in TW Hydrae

We present a new Subaru/HiCIAO high-contrast H-band polarized intensity (PI) image of a nearby transitional disk associated with TW Hydrae. The scattered light from the disk was detected from 0.2" to 1.5" (11 - 81 AU) and the PI image shows a clear axisymmetric depression in polarized intensity at ~ 0.4" (~ 20 AU) from the central star, similar to the ~ 80 AU gap previously reported from HST images. Azimuthal polarized intensity profile also shows the disk beyond 0.2" is almost axisymmetric. We discuss two possible scenarios explaining the origin of the polarized intensity depression: 1) a gap structure may exist at ~ 20 AU from the central star because of shallow slope seen in the polarized intensity profile, and 2) grain growth may be occurring in the inner region of the disk. Multi-band observations at NIR and millimeter/sub-millimeter wavelengths play a complementary role in investigating dust opacity and may help reveal the origin of the gap more precisely.

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arXiv2014

Study of morphology and stellar content of the Galactic HII region IRAS 16148-5011

An investigation of the IRAS 16148-5011 region - a cluster at a distance of 3.6 kpc - is presented here, carried out using multiwavelength data in near-infrared (NIR) from the 1.4m Infrared Survey Facility telescope, mid-infrared (MIR) from the archival Spitzer GLIMPSE survey, far-infrared (FIR) from the Herschel archive, and low-frequency radio continuum observations at 1280 and 843 MHz from the Giant Metrewave Radio Telescope (GMRT) and Molonglo Survey archive, respectively. A combination of NIR and MIR data is used to identify 7 Class I and 133 Class II sources in the region. Spectral Energy Distribution (SED) analysis of selected sources reveals a 9.6 Msolar, high-mass source embedded in nebulosity. However, Lyman continuum luminosity calculation using radio emission - which shows a compact HII, region - indicates the spectral type of the ionizing source to be earlier than B0-O9.5. Free-free emission SED modelling yields the electron density as 138 cm^{-3}, and thus the mass of the ionized hydrogen as ~16.4 Msolar. Thermal dust emission modelling, using the FIR data from Herschel and performing modified blackbody fits, helped us construct the temperature and column density maps of the region, which show peak values of 30 K and 3.3x10^{22} cm^{-2}, respectively. The column density maps reveal an AV > 20 mag extinction associated with the nebular emission, and weak filamentary structures connecting dense clumps. The clump associated with this IRAS object is found to have dimensions of ~1.1 pc x 0.8 pc, and a mass of 1023 Msolar.

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arXiv2014

The Structure of Pre-transitional Protoplanetary Disks. II. Azimuthal Asymmetries, Different Radial Distributions of Large and Small Dust Grains in PDS~70

The formation scenario of a gapped disk, i.e., transitional disk, and its asymmetry is still under debate. Proposed scenarios such as disk-planet interaction, photoevaporation, grain growth, anticyclonic vortex, eccentricity, and their combinations would result in different radial distributions of the gas and the small (sub-$μ$m size) and large (millimeter size) dust grains as well as asymmetric structures in a disk. Optical/near-infrared (NIR) imaging observations and (sub-)millimeter interferometry can trace small and large dust grains, respectively; therefore multi-wavelength observations could help elucidate the origin of complicated structures of a disk. Here we report SMA observations of the dust continuum at 1.3~mm and $^{12}$CO~$J=2\rightarrow1$ line emission of the pre-transitional protoplanetary disk around the solar-mass star PDS~70. PDS~70, a weak-lined T Tauri star, exhibits a gap in the scattered light from its disk with a radius of $\sim$65~AU at NIR wavelengths. However, we found a larger gap in the disk with a radius of $\sim$80~AU at 1.3~mm. Emission from all three disk components (the gas and the small and large dust grains) in images exhibits a deficit in brightness in the central region of the disk, in particular, the dust-disk in small and large dust grains has asymmetric brightness. The contrast ratio of the flux density in the dust continuum between the peak position to the opposite side of the disk reaches 1.4. We suggest the asymmetries and different gap-radii of the disk around PDS~70 are potentially formed by several (unseen) accreting planets inducing dust filtration.

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arXiv2014

A Statistical Analysis of SEEDS and Other High-Contrast Exoplanet Surveys: Massive Planets or Low-Mass Brown Dwarfs?

We conduct a statistical analysis of a combined sample of direct imaging data, totalling nearly 250 stars. The stars cover a wide range of ages and spectral types, and include five detections ($κ$ And b, two $\sim$60 M$_{\rm J}$ brown dwarf companions in the Pleiades, PZ Tel B, and CD$-$35 2722B). For some analyses we add a currently unpublished set of SEEDS observations, including the detections GJ 504b and GJ 758B. We conduct a uniform, Bayesian analysis of all stellar ages using both membership in a kinematic moving group and activity/rotation age indicators. We then present a new statistical method for computing the likelihood of a substellar distribution function. By performing most of the integrals analytically, we achieve an enormous speedup over brute-force Monte Carlo. We use this method to place upper limits on the maximum semimajor axis of the distribution function derived from radial-velocity planets, finding model-dependent values of $\sim$30--100 AU. Finally, we model the entire substellar sample, from massive brown dwarfs to a theoretically motivated cutoff at $\sim$5 M$_{\rm Jup}$, with a single power law distribution. We find that $p(M, a) \propto M^{-0.65\pm0.60} a^{-0.85\pm0.39}$ (1$σ$ errors) provides an adequate fit to our data, with 1.0--3.1\% (68\% confidence) of stars hosting 5--70 $M_{\rm Jup}$ companions between 10 and 100 AU. This suggests that many of the directly imaged exoplanets known, including most (if not all) of the low-mass companions in our sample, formed by fragmentation in a cloud or disk, and represent the low-mass tail of the brown dwarfs.

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arXiv2014

NGC 7538 : Multiwavelength Study of Stellar Cluster Regions associated with IRS 1-3 and IRS 9 sources

We present deep and high-resolution (FWHM ~ 0.4 arcsec) near-infrared (NIR) imaging observations of the NGC 7538 IRS 1-3 region (in JHK bands), and IRS 9 region (in HK bands) using the 8.2m Subaru telescope. The NIR analysis is complemented with GMRT low-frequency observations at 325, 610, and 1280 MHz, molecular line observations of H13CO+ (J=1-0), and archival Chandra X-ray observations. Using the 'J-H/H-K' diagram, 144 Class II and 24 Class I young stellar object (YSO) candidates are identified in the IRS 1-3 region. Further analysis using 'K/H-K' diagram yields 145 and 96 red sources in the IRS 1-3 and IRS 9 regions, respectively. A total of 27 sources are found to have X-ray counterparts. The YSO mass function (MF), constructed using a theoretical mass-luminosity relation, shows peaks at substellar (~0.08-0.18 Msolar) and intermediate (~1-1.78 Msolar) mass ranges for the IRS 1-3 region. The MF can be fitted by a power law in the low mass regime with a slope of Gamma ~ 0.54-0.75, which is much shallower than the Salpeter value of 1.35. An upper limit of 10.2 is obtained for the star to brown dwarf ratio in the IRS 1-3 region. GMRT maps show a compact HII region associated with the IRS 1-3 sources, whose spectral index of 0.87+-0.11 suggests optical thickness. This compact region is resolved into three separate peaks in higher resolution 1280 MHz map, and the 'East' sub-peak coincides with the IRS 2 source. H13CO+ (J=1-0) emission reveals peaks in both IRS 1-3 and IRS 9 regions, none of which are coincident with visible nebular emission, suggesting the presence of dense cloud nearby. The virial masses are approximately of the order of 1000 Msolar and 500 Msolar for the clumps in IRS 1-3 and IRS 9 regions, respectively.

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arXiv2014

The VVV Templates Project. Towards an Automated Classification of VVV Light-Curves. I. Building a database of stellar variability in the near-infrared

Context. The Vista Variables in the Vía Láctea (VVV) ESO Public Survey is a variability survey of the Milky Way bulge and an adjacent section of the disk carried out from 2010 on ESO Visible and Infrared Survey Telescope for Astronomy (VISTA). VVV will eventually deliver a deep near-IR atlas with photometry and positions in five passbands (ZYJHK_S) and a catalogue of 1-10 million variable point sources - mostly unknown - which require classifications. Aims. The main goal of the VVV Templates Project, that we introduce in this work, is to develop and test the machine-learning algorithms for the automated classification of the VVV light-curves. As VVV is the first massive, multi-epoch survey of stellar variability in the near-infrared, the template light-curves that are required for training the classification algorithms are not available. In the first paper of the series we describe the construction of this comprehensive database of infrared stellar variability. Methods. First we performed a systematic search in the literature and public data archives, second, we coordinated a worldwide observational campaign, and third we exploited the VVV variability database itself on (optically) well-known stars to gather high-quality infrared light-curves of several hundreds of variable stars. Results. We have now collected a significant (and still increasing) number of infrared template light-curves. This database will be used as a training-set for the machine-learning algorithms that will automatically classify the light-curves produced by VVV. The results of such an automated classification will be covered in forthcoming papers of the series.

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arXiv2014

The Moving Group Targets of the SEEDS High-Contrast Imaging Survey of Exoplanets and Disks: Results and Observations from the First Three Years

We present results from the first three years of observations of moving group targets in the SEEDS high-contrast imaging survey of exoplanets and disks using the Subaru telescope. We achieve typical contrasts of ~10^5 at 1" and ~10^6 beyond 2" around 63 proposed members of nearby kinematic moving groups. We review each of the kinematic associations to which our targets belong, concluding that five, βPictoris (~20 Myr), AB Doradus (~100 Myr), Columba (~30 Myr), Tucana-Horogium (~30 Myr), TW Hydrae (~10 Myr), are sufficiently well-defined to constrain the ages of individual targets. Somewhat less than half of our targets are high-probability members of one of these moving groups. For all of our targets, we combine proposed moving group membership with other age indicators where available, including Ca II HK emission, X-ray activity, and rotation period, to produce a posterior probability distribution of age. SEEDS observations discovered a substellar companion to one of our targets, κAnd, a late B star. We do not detect any other substellar companions, but do find seven new close binary systems, of which one still needs to be confirmed. A detailed analysis of the statistics of this sample, and of the companion mass constraints given our age probability distributions and exoplanet cooling models, will be presented in a forthcoming paper.

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arXiv2014

Star formation activity in the southern Galactic HII region G351.63-1.25

The southern Galactic high mass star-forming region, G351.6-1.3, is a HII region-molecular cloud complex with a luminosity of 2.0 x 10^5 L_sun, located at a distance of 2.4 kpc. In this paper, we focus on the investigation of the associated HII region, embedded cluster and the interstellar medium in the vicinity of G351.6-1.3. We address the identification of exciting source(s) as well as the census of stellar populations. The ionised gas distribution has been mapped using the Giant Metrewave Radio Telescope (GMRT), India at three continuum frequencies: 1280, 610 and 325 MHz. The HII region shows an elongated morphology and the 1280 MHz map comprises six resolved high density regions encompassed by diffuse emission spanning 1.4 pc x 1.0 pc. The zero age main-sequence (ZAMS) spectral type of the brightest radio core is O7.5. We have carried out near-infrared observations in the JHKs bands using the SIRIUS instrument on the 1.4 m Infrared Survey Facility (IRSF) telescope. The near-infrared images reveal the presence of a cluster embedded in nebulous fan-shaped emission. The log-normal slope of the K-band luminosity function of the embedded cluster is found to be 0.27 +- 0.03 and the fraction of the near-infrared excess stars is estimated to be 43%. These indicate that the age of the cluster is consistent with 1 Myr. The champagne flow model from a flat, thin molecular cloud is used to explain the morphology of radio emission with respect to the millimetre cloud and infrared brightness.

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arXiv2014

The architecture of the LkCa 15 transitional disk revealed by high-contrast imaging

We present four new epochs of Ks-band images of the young pre-transitional disk around LkCa 15, and perform extensive forward modeling to derive the physical parameters of the disk. We find indications of strongly anisotropic scattering (Henyey-Greenstein g = 0.67 [-0.11,+0.18]) and a significantly tapered gap edge ('round wall'), but see no evidence that the inner disk, whose existence is predicted by the spectral energy distribution, shadows the outer regions of the disk visible in our images. We marginally confirm the existence of an offset between the disk center and the star along the line of nodes; however, the magnitude of this offset (x = 27 [-20,+19] mas) is notably lower than that found in our earlier H-band images (Thalmann et al. 2010). Intriguingly, we also find, at high significance, an offset of y = 69 [-25, +49] mas perpendicular to the line of nodes. If confirmed by future observations, this would imply a highly elliptical -- or otherwise asymmetric -- disk gap with an effective eccentricity of e = ~0.3. Such asymmetry would most likely be the result of dynamical sculpting by one or more unseen planets in the system. Finally, we find that the bright arc of scattered light we see in direct imaging observations originates from the near side of the disk, and appears brighter than the far side because of strong forward scattering.

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arXiv2013

Direct Imaging Detection of Methane in the Atmosphere of GJ 504 b

Most exoplanets detected by direct imaging so far have been characterized by relatively hot (> ~1000 K) and cloudy atmospheres. A surprising feature in some of their atmospheres has been a distinct lack of methane, possibly implying non-equilibrium chemistry. Recently, we reported the discovery of a planetary companion to the Sun-like star GJ 504 using Subaru/HiCIAO within the SEEDS survey. The planet is substantially colder (<600 K) than previously imaged planets, and has indications of fewer clouds, which implies that it represents a new class of planetary atmospheres with expected similarities to late T-type brown dwarfs in the same temperature range. If so, one might also expect the presence of significant methane absorption, which is characteristic of such objects. Here, we report the detection of deep methane absorption in the atmosphere of GJ 504 b, using the Spectral Differential Imaging mode of HiCIAO to distinguish the absorption feature around 1.6 um. We also report updated JHK photometry based on new Ks-band data and a re-analysis of the existing data. The results support the notion that GJ 504 b has atmospheric properties distinct from other imaged exoplanets, and will become a useful reference object for future planets in the same temperature range.

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arXiv2013

Re-appearance of McNeil's nebula (V1647 Orionis) and its outburst environment

We present a detailed study of McNeil's nebula (V1647 Ori) in its ongoing outburst phase starting from September 2008 to March 2013. Our 124 nights of photometric observations were carried out in optical V, R, I and near-infrared J, H, K bands, and 59 nights of medium resolution spectroscopic observations were done in 5200 - 9000 Ang wavelength range. All observations were carried out with 2-m Himalayan Chandra Telescope and 2-m IUCAA Girawali Telescope. Our observations show that over last four and a half years, V1647 Ori and the region C near Herbig-Haro object, HH 22A, have been undergoing a slow dimming at a rate of ~0.04 mag/yr and ~0.05 mag/yr respectively in R-band, which is 6 times slower than the rate during similar stage of V1647 Ori in 2003 outburst. We detected change in flux distribution over the reflection nebula implying changes in circumstellar matter distribution between 2003 and 2008 outbursts. Apart from steady wind of velocity ~350 km/s we detected two episodic magnetic reconnection driven winds. Forbidden [O I] 6300 Ang and [Fe II] 7155 Ang lines were also detected implying shock regions probably from jets. We tried to explain the outburst timescales of V1647 Ori using the standard models of FUors kind of outburst and found that pure thermal instability models like Bell & Lin (1994) cannot explain the variations in timescales. In the framework of various instability models we conclude that one possible reason for sudden ending of 2003 outburst in 2005 November was due to a low density region or gap in the inner region (~ 1 AU) of the disc.

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arXiv2013

Characterization of the gaseous companion κ Andromedae b: New Keck and LBTI high-contrast observations

We previously reported the direct detection of a low mass companion at a projected separation of 55+-2 AU around the B9 type star κ Andromedae. The properties of the system (mass ratio, separation) make it a benchmark for the understanding of the formation and evolution of gas giant planets and brown dwarfs on wide-orbits. We present new angular differential imaging (ADI) images of the Kappa Andromedae system at 2.146 (Ks), 3.776 (L'), 4.052 (NB 4.05) and 4.78 μm (M') obtained with Keck/NIRC2 and LBTI/LMIRCam, as well as more accurate near-infrared photometry of the star with the MIMIR instrument. We derive a more accurate J = 15.86 +- 0.21, H = 14.95 +- 0.13, Ks = 14.32 +- 0.09 mag for κ And b. We redetect the companion in all our high contrast observations. We confirm previous contrasts obtained at Ks and L' band. We derive NB 4.05 = 13.0 +- 0.2 and M' = 13.3 +- 0.3 mag and estimate Log10(L/Lsun) = -3.76 +- 0.06. We build the 1-5 microns spectral energy distribution of the companion and compare it to seven PHOENIX-based atmospheric models in order to derive Teff = 1900+100-200 K. Models do not set constrains on the surface gravity. ``Hot-start" evolutionary models predict masses of 14+25-2 MJup based on the luminosity and temperature estimates, and considering a conservative age range for the system (30+120-10 Myr). ``warm-start" evolutionary tracks constrain the mass to M >= 11 MJup. Therefore, the mass of κ Andromedae b mostly falls in the brown-dwarf regime, due to remaining uncertainties in age and mass-luminosity models. According to the formation models, disk instability in a primordial disk could account for the position and a wide range of plausible masses of κ And b.

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arXiv2013

Direct Imaging of a Cold Jovian Exoplanet in Orbit around the Sun-like Star GJ 504

Several exoplanets have recently been imaged at wide separations of >10 AU from their parent stars. These span a limited range of ages (<50 Myr) and atmospheric properties, with temperatures of 800--1800 K and very red colors (J - H > 0.5 mag), implying thick cloud covers. Furthermore, substantial model uncertainties exist at these young ages due to the unknown initial conditions at formation, which can lead to an order of magnitude of uncertainty in the modeled planet mass. Here, we report the direct imaging discovery of a Jovian exoplanet around the Sun-like star GJ 504, detected as part of the SEEDS survey. The system is older than all other known directly-imaged planets; as a result, its estimated mass remains in the planetary regime independent of uncertainties related to choices of initial conditions in the exoplanet modeling. Using the most common exoplanet cooling model, and given the system age of 160 [+350, -60] Myr, GJ 504 b has an estimated mass of 4 [+4.5, -1.0] Jupiter masses, among the lowest of directly imaged planets. Its projected separation of 43.5 AU exceeds the typical outer boundary of ~30 AU predicted for the core accretion mechanism. GJ 504 b is also significantly cooler (510 [+30, -20] K) and has a bluer color (J-H = -0.23 mag) than previously imaged exoplanets, suggesting a largely cloud-free atmosphere accessible to spectroscopic characterization. Thus, it has the potential of providing novel insights into the origins of giant planets, as well as their atmospheric properties.

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