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  • 1
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    A Young Stellar Cluster in the Nucleus of NGC 4449 (2001)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: We have obtained 1-2 A resolution optical Echellette spectra of the nuclear star cluster in the nearby starburst galaxy NGC4449. The light is clearly dominated by a very young (6 - 10 Myr) population of stars. For our age dating, we have used recent population synthesis models to interpret the observed equivalent width of stellar absorption features such as the H I Balmer series and the Ca II triplet around 8500 A. We also compare the observed spectrum of the nuclear cluster to synthesized spectra for stellar populations of varying ages. All these approaches yield a consistent cluster age. Metallicity estimates based on the relative intensities of various ionization lines yield no evidence for significant enrichment in the center of this low mass galaxy: the metallicity of the nuclear cluster is about one fourth of the solar value, in agreement with independent estimates for the disk material of NGC4449.
    Keywords: Astrophysics
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  • 2
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    High-Contrast Polarimetry Observation of the T Tau Circumstellar Environment (2018)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: We conducted high-contrast polarimetry observations of T Tau in the H-band, using the High Contrast Instrument for the Subaru Next Generation Adaptive Optics instrument mounted on the Subaru Telescope, revealing structures as near as 0farcs1 from the stars T Tau N and T Tau S. The whole T Tau system is found to be surrounded by nebula-like envelopes, and several outflow-related structures are detected in these envelopes. We analyzed the detailed polarization patterns of the circumstellar structures near each component of this triple young star system and determined constraints on the circumstellar disks and outflow structures. We suggest that the nearly face-on circumstellar disk of T Tau N is no larger than 0".8, or 117 au, in the northwest, based on the existence of a hole in this direction, and no larger than 0".27, or 40 au, in the south. A new structure, "N5," extends to about 0."42, or 59 au, southwest of the star, and is believed to be part of the disk. We suggest that T Tau S is surrounded by a highly inclined circumbinary disk with a radius of about 0."3, or 44 au, with a position angle of about 30, that is misaligned with the orbit of the T Tau S binary. After analyzing the positions and polarization vector patterns of the outflow-related structures, we suggest that T Tau S should trigger the well-known EW outflow, and is also likely to be responsible for a southwest precessing outflow "coil" and a possible south outflow.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN64810 , The Astrophysical Journal (ISSN 0004-637X) (e-ISSN 1538-4357); 861; 2; 133
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  • 3
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    Subaru/HiCIAO HK(sub S) Imaging of LKHa 330: Multi-Band Detection of the Gap and Spiral-Like Structures (2018)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: We present H- and K s-bands observations of the LkH 330 disk with a multi-band detection of the large gap and spiral-like structures. The morphology of the outer disk (r ~ 0."3) at PA = 045 and PA = 180290 is likely density wave-induced spirals, and comparison between our observational results and simulations suggests a planet formation. We have also investigated the azimuthal profiles at the ring and the outer-disk regions as well as radial profiles in the directions of the spiral-like structures and semimajor axis. Azimuthal analysis shows a large variety in wavelength and implies that the disk has non-axisymmetric dust distributions. The radial profiles in the major-axis direction (PA = 271) suggest that the outer region (r 0."25) may be influenced by shadows of the inner region of the disk. The spiral-like directions (PA = 10 and 230) show different radial profiles, which suggests that the surfaces of the spiral-like structures are highly flared and/or have different dust properties. Finally, a color map of the disk shows a lack of an outer eastern region in the H-band disk, which may hint at the presence of an inner object that casts a directional shadow onto the disk.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN64807 , The Astrophysical Journal (ISSN 0004-6256) (e-ISSN 1538-3881); 156; 2; 63
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  • 4
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    The SEEDS Direct Imaging Survey for Planets and Scattered Dust Emission in Debris Disk Systems (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: Debris disks around young main-sequence stars often have gaps and cavities which for a long time have been interpreted as possibly being caused by planets. In recent years, several giant planet discoveries have been made in systems hosting disks of precisely this nature, further implying that interactions with planets could be a common cause of such disk structures. As part of the SEEDS high-contrast imaging survey, we are surveying a population of debris disk-hosting stars with gaps and cavities implied by their spectral energy distributions, in order to attempt to spatially resolve the disk as well as to detect any planets that may be responsible for the disk structure. Here we report on intermediate results from this survey. Five debris disks have been spatially resolved, and a number of faint point sources have been discovered, most of which have been tested for common proper motion, which in each case has excluded physical companionship with the target stars. From the detection limits of the 50 targets that have been observed, we find that beta Pic b-like planets (approximately 10M(sub jup) planets around G-A-type stars) near the gap edges are less frequent than 15-30%, implying that if giant planets are the dominant cause of these wide (27 AU on average) gaps, they are generally less massive than beta Pic b.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN9835 , Astrophysical Journal
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  • 5
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    Detailed Structure of the Outer Disk Around HD 169142 with Polarized Light in H-band (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Coronagraphic imagery of the circumstellar disk around HD 169142 in H-band polarized intensity (PI) with Subaru/HiCIAO is presented. The emission scattered by dust particles at the disk surface in 0.2r1.2, or 29r174 AU, is successfully detected. The azimuthally-averaged radial profile of the PI shows a double power-law distribution, in which the PIs in r = 2952 AU and r = 81.2145 AU respectively show r3-dependence. These two power-law regions are connected smoothly with a transition zone (TZ), exhibiting an apparent gap in r = 4070 AU. The PI in the inner power-law region shows a deep minimum whose location seems to coincide with the point source at lambda = 7 mm. This can be regarded as another sign of a protoplanet in TZ. The observed radial profile of the PI is reproduced by a minimally flaring disk with an irregular surface density distribution or with an irregular temperature distribution or with the combination of both. The depletion factor of surface density in the inner power-law region (r 〈50 AU) is derived to be 0.16 from a simple model calculation. The obtained PI image also shows small scale asymmetries in the outer power-law region. Possible origins for these asymmetries include corrugation of the scattering surface in the outer region, and shadowing effect by a puffed up structure in the inner power-law region.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN33497 , Publications of the Astronomical Society of Japan (e-ISSN 2053-051X); 67; 5; 1-26
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  • 6
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    High-Contrast Imaging of Intermediate-Mass Giants with Long-Term Radial Velocity Trends (2016)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A radial velocity (RV) survey for intermediate-mass giants has been operated for over a decade at Okayama Astrophysical Observatory (OAO). The OAO survey has revealed that some giants show long-term linear RV accelerations (RV trends), indicating the presence of outer companions. Direct imaging observations can help clarify what objects generate these RV trends. We present the results of high-contrast imaging observations of six intermediate-mass giants with long-term RV trends using the Subaru Telescope and HiCIAO camera. We detected co-moving companions to gamma Hya B (0.61+0.12 0.14 Stellar Mass), HD 5608 B (0.10 +/- 0.01 Stellar Mass), and HD 109272 B (0.28 +/- 0.06 Stellar Mass). For the remaining targets( Dra, 18 Del, and HD 14067) we exclude companions more massive than 30-60 M(sub Jup) at projected separations of 1-7. We examine whether these directly imaged companions or unidentified long-period companions can account for the RV trends observed around the six giants. We find that the Kozai mechanism can explain the high eccentricity of the inner planets Dra b, HD 5608 b, and HD 14067 b.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN33488 , Astrophysical Journal (ISSN 0004-637X) (e-ISSN 1538-4357); 825; 2; 127
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  • 7
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    Near-Infrared Imaging Polarimetry of Inner Region of GG Tau A Disk (2016)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: By performing non-masked polarization imaging with Subaru HiCIAO, polarized scattered light from the inner region of the disk around the GGTau A system was successfully detected in the H band, with a spatial resolution of approximately0 07, revealing the complicated inner disk structures around this young binary. This paper reports the observation of an arc-like structure to the north of GG Tau Ab, and part of a circumstellar structure that is noticeable around GG Tau Aa, extending to a distance of approximately 28 au from the primary star. The speckle noise around GG Tau Ab constrains its disk radius to 13 au. Based on the size of the circumbinary ring and the circumstellar disk around GG Tau Aa, these mimajor axis of the binary's orbit is likely to be 62 au. A comparison of the present observations with previous Atacama Large Millimeter Array and near-infrared H2 emission observations suggests that the north arc could be part of a large streamer flowing from the circumbinary ring to sustain the circumstellar disks. According to the previous studies,the circumstellar disk around GG Tau Aa has enough mass and can sustain itself for a duration sufficient for planet formation; thus, our study indicates that planets can form within close (separation 100 au) young binary systems.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN43990 , The Astronomical Journal (ISSN 1538-3881); 153; 1; 7
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  • 8
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    Spiral Structure and Differential Dust Size Distribution in the LkH(alpha) 330 Disk (2016)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Dust trapping accelerates the coagulation of dust particles, and, thus, it represents an initial step toward the formation of planetesimals. We report H-band (1.6 microns) linear polarimetric observations and 0.87 mm interferometric continuum observations toward a transitional disk around LkH(alpha) 330. As a result, a pair of spiral arms were detected in the H-band emission, and an asymmetric (potentially arm-like) structure was detected in the 0.87 mm continuum emission. We discuss the origin of the spiral arm and the asymmetric structure and suggest that a massive unseen planet is the most plausible explanation. The possibility of dust trapping and grain growth causing the asymmetric structure was also investigated through the opacity index (beta) by plotting the observed spectral energy distribution slope between 0.87 mm from our Submillimeter Array observation and1.3 mm from literature. The results imply that grains are indistinguishable from interstellar medium-like dust in the east side (beta = 2.0 +/- 0.5) but are much smaller in the west side beta = 0.7+0.5 -0.4, indicating differential dust size distribution between the two sides of the disk. Combining the results of near-infrared and submillimeter observations, we conjecture that the spiral arms exist at the upper surface and an asymmetric structure resides in the disk interior. Future observations at centimeter wavelengths and differential polarization imaging in other bands (Y-K) with extreme AO imagers are required to understand how large dust grains form and to further explore the dust distribution in the disk.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN43988 , The Astronomical Journal (ISSN 0004-6256) (e-ISSN 1538-3881); 152; 6; 222
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  • 9
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    A Resolved Near-Infrared Image of the Inner Cavity in the GM Aur Transitional Disk (2016)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We present high-contrast H-band polarized intensity (PI) images of the transitional disk around the young solar like star GM Aur. The near-infrared direct imaging of the disk was derived by polarimetric differential imaging using the Subaru 8.2 m Telescope and HiCIAO. An angular resolution and an inner working angle of 0 07 and radius approximately 0 05, respectively, were obtained. We clearly resolved a large inner cavity, with a measured radius of 18+/ 2 au, which is smaller than that of a submillimeter interferometric image (28 au). This discrepancy in the cavity radii at near-infrared and submillimeter wavelengths may be caused by a 34M(sub Jup) planet about 20 au away from the star, near the edge of the cavity. The presence of a near-infrared inner cavity is a strong constraint on hypotheses for inner cavity formation in a transitional disk. A dust filtration mechanism has been proposed to explain the large cavity in the submillimeter image, but our results suggest that this mechanism must be combined with an additional process. We found that the PI slope of the outer disk is significantly different from the intensity slope obtained from HSTNICMOS, and this difference may indicate the grain growth process in the disk.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN41439 , The Astrophysical Journal Letters (ISSN 2041-8205); 831; 1; L7
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  • 10
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    The First Brown Dwarf Discovered by the Backyard Worlds: Planet 9 Citizen Science Project (2017)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The Wide-field Infrared Survey Explorer (WISE) is a powerful tool for finding nearby brown dwarfs and searching for new planets in the outer solar system, especially with the incorporation of NEOWISE and NEOWISE Reactivation data. However, so far, searches for brown dwarfs in WISE data have yet to take advantage of the full depth of the WISE images. To efficiently search this unexplored space via visual inspection, we have launched anew citizen science project, called "Backyard Worlds: Planet 9," which asks volunteers to examine short animations composed of difference images constructed from time-resolved WISE co adds. We report the first new substellar object discovered by this project, WISEA J110125.95+540052.8, a T5.5 brown dwarf located approximately 34 pc from the Sun with a total proper motion of approx.0. "7/ yr. WISEA J110125.95+540052.8 has a WISE W2 magnitude of W2 = 15.37+/- 0.09; our sensitivity to this source demonstrates the ability of citizen scientists to identify moving objects via visual inspection that are 0.9 mag fainter than the W2 single-exposure sensitivity, a threshold that has limited prior motion-based brown dwarf searches with WISE.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN45486 , The Astrophysical Journal Letters (ISSN 2041-8205) (e-ISSN 2041-8213); 841; 2; L19
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