Smithsonian Astrophysical Observatory

About: Smithsonian Astrophysical Observatory is a facility organization based out in Cambridge, Massachusetts, United States. It is known for research contribution in the topics: Galaxy & Stars. The organization has 1665 authors who have published 3622 publications receiving 132183 citations. The organization is also known as: SAO.

Formation of super-earth mass planets at 125–250 au from a solar-type star

Abstract: We investigate pathways for the formation of icy super-Earth mass planets orbiting at 125–250 AU around a 1 star. An extensive suite of coagulation calculations demonstrates that swarms of 1 cm–10 m planetesimals can form super-Earth mass planets on timescales of 1–3 Gyr. Collisional damping of 10−2−102 cm particles during oligarchic growth is a highlight of these simulations. In some situations, damping initiates a second runaway growth phase where 1000–3000 km protoplanets grow to super-Earth sizes. Our results establish the initial conditions and physical processes required for in situ formation of super-Earth planets at large distances from the host star. For nearby dusty disks in HD 107146, HD 202628, and HD 207129, ongoing super-Earth formation at 80–150 AU could produce gaps and other structures in the debris. In the solar system, forming a putative planet X at AU ( AU) requires a modest (very massive) protosolar nebula.

Exploring the unusually high black-hole-to-bulge mass ratios in ngc 4342 and ngc 4291: the asynchronous growth of bulges and black holes

Abstract: We study two nearby early-type galaxies, NGC 4342 and NGC 4291, that host unusually massive black holesrelative to their low stellar mass. The observed black-hole-to-bulge mass ratios of NGC 4342 and NGC 4291are 6 . 9 +3 . 8−2 . 3 % and 1 . 9% ±0 . 6%, respectively, which significantly exceed the typical observed ratio of ∼0 . 2%. Asa consequence of the exceedingly large black-hole-to-bulge mass ratios, NGC 4342 and NGC 4291 are ≈5 . 1 σ and ≈3 . 4 σ outliers from the M • – M bulge scaling relation, respectively. In this paper, we explore the origin of theunusually high black-hole-to-bulge mass ratio. Based on Chandra X-ray observations of the hot gas content ofNGC 4342 and NGC 4291, we compute gravitating mass profiles, and conclude that both galaxies reside in massivedark matter halos, which extend well beyond the stellar light. The presence of dark matter halos around NGC 4342and NGC 4291 and a deep optical image of the environment of NGC 4342 indicate that tidal stripping, in which 90% of the stellar mass was lost, cannot explain the observed high black-hole-to-bulge mass ratios. Therefore,we conclude that these galaxies formed with low stellar masses, implying that the bulge and black hole did notgrow in tandem. We also find that the black hole mass correlates well with the properties of the dark matter halo,suggesting that dark matter halos may play a major role in regulating the growth of the supermassive black holes.

Chronology of star formation and disk evolution in the Eagle Nebula

Abstract: Context. Massive star-forming regions are characterized by intense ionizing fluxes, strong stellar winds and, occasionally, supernovae explosions, all of which have important effects on the surrounding media, on the star-formation process and on the evolution of young stars and their circumstellar disks. We present a multiband study of the massive young cluster NGC 6611 and its parental cloud (the Eagle Nebula) with the aim of studying how OB stars affect the early stellar evolution and the formation of other stars. Aims. We search for evidence of triggering of star formation by the massive stars inside NGC 6611 on a large spatial scale (∼10 parsec) and ongoing disk photoevaporation in NGC 6611 and how its efficiency depends on the mass of the central stars. Methods. We assemble a multiband catalog of the Eagle Nebula with photometric data, ranging from B band to 8.0 μm, and X-ray data obtained with two new and one archival Chandra/ACIS-I observation. We select the stars with disks from infrared photometry and disk-less ones from X-ray emission, which are associated both with NGC 6611 and the outer region of the Eagle Nebula. We study induced photoevaporation searching for the spatial variation of disk frequency for distinct stellar mass ranges. The triggering of star formation by OB stars has been investigated by deriving the history of star formation across the nebula. Results. We find evidence of sequential star formation in the Eagle Nebula going from the southeast (2.6 Myears) to the northwest (0.3 Myears), with the median age of NGC 6611 members ∼1 Myear. In NGC 6611, we observe a drop of the disk frequency close to massive stars (up to an average distance of 1 parsec), without observable effects at larger distances. Furthermore, disks are more frequent around low-mass stars (≤1 M� ) than around high-mass stars, regardless of the distance from OB stars. Conclusions. The star-formation chronology we find in the Eagle Nebula does not support the hypothesis of a large-scale process triggered by OB stars in NGC 6611. Instead, we speculate that it was triggered by the encounter (about 3 Myears ago) with a giant molecular shell created by supernovae explosions about 6 Myears ago. We find evidence of disk photoevaporation close to OB stars, where disks are heated by incident extreme ultraviolet (EUV) radiation. No effects are observed at large distances from OB stars, where photoevaporation is induced by the far ultraviolet (FUV) radiation, and long timescales are usually required to completely dissipate the disks.

Aluminum-26 and beryllium-10 in greenland ice.

Abstract: Activities of beryllium-10 and aluminum-26 dissolved in 200-year-old Greenland ice were found to be 18.4 (+ 8.4, - 4.8) x 10-6 and 3.2 ± 0.9 x 10-7 disintegration per minute per liter, respectively. From these values and the precipitation rate (30 milliliters of water per square centimeter per year), the production rates of these isotopes are calculated to be 3.6 (+ 1.6, - 0.9) x 10-2 and 1.7 ± 0.5 x 10-4 atom per second * square centimeter. These rates agree with the rates calculated for the production of these isotopes by cosmic rays in the atmosphere. Probably all the Al26 in the ice is accounted for by such atmospheric production; however, an upper limit for the influx of cosmic dust bearing aluminum-26 is calculated at 3.2 x 105 tons per year for Earth. Only upper limits could be found for Al26 and Be10 in the undissolved particulate matter in the ice; their addition to the activities in the dissolved material leaves our conclusions unchanged.

Dusty WDs in the WISE all sky survey ∩ SDSS

Abstract: A recent cross-correlation between the Sloan Digital Sky Survey (SDSS) Data Release 7 White Dwarf Catalog with the Wide-Field Infrared Survey Explorer (WISE) all-sky photometry at 3.4, 4.6, 12, and 22 μm performed by Debes et al. resulted in the discovery of 52 candidate dusty white dwarfs (WDs). However, the 6'' WISE beam allows for the possibility that many of the excesses exhibited by these WDs may be due to contamination from a nearby source. We present MMT+SAO Wide-Field InfraRed Camera J- and H-band imaging observations (0.''5-1.''5 point spread function) of 16 of these candidate dusty WDs and confirm that four have spectral energy distributions (SEDs) consistent with a dusty disk and are not accompanied by a nearby source contaminant. The remaining 12 WDs have contaminated WISE photometry and SEDs inconsistent with a dusty disk when the contaminating sources are not included in the photometry measurements. We find the frequency of disks around single WDs in the WISE ∩ SDSS sample to be 2.6%-4.1%. One of the four new dusty WDs has a mass of 1.04 M {sub ☉} (progenitor mass 5.4 M {sub ☉}) and its discovery offers the first confirmation that massive WDs (and their massive progenitor stars)more » host planetary systems.« less