UV-optical Emission of AB Aur b Is Consistent with Scattered Stellar Light
Yifan ZhouBrendan P. BowlerHaifeng YangAniket SanghiGregory J. HerczegAdam L. KrausJaehan BaeFeng LongKatherine B. FolletteKimberly Ward-DuongZhaohuan ZhuLauren I. BiddleLaird M. CloseLillian Yushu JiangYa-Lin Wu
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Abstract The proposed protoplanet AB Aur b is a spatially concentrated emission source imaged in the millimeter-wavelength disk gap of the Herbig Ae/Be star AB Aur. Its near-infrared spectrum and absence of strong polarized light have been interpreted as evidence supporting the protoplanet interpretation. However, the complex scattered-light structures in the AB Aur disk pose challenges in resolving the emission source and interpreting the true nature of AB Aur b. We present new images of the AB Aur system obtained using the Hubble Space Telescope Wide Field Camera 3 in the ultraviolet (UV) and optical bands. AB Aur b and the known disk spirals are recovered in the F336W, F410M, and F645N bands. The spectral energy distribution of AB Aur b shows absorption in the Balmer jump, mimicking that of early-type stars. By comparing the colors of AB Aur b to those of the host star, the disk spirals, and predictions from scattered light and self-luminous models, we find that the emission from AB Aur b is inconsistent with planetary photospheric or accretion shock models. Instead, it is consistent with those measured in the circumstellar disks that trace scattered light. We conclude that the UV and visible emission from AB Aur b does not necessitate the presence of a protoplanet. We synthesize observational constraints on AB Aur b and discuss inconsistent interpretations among different data sets. Considering the significance of the AB Aur b discovery, we advocate for further observational evidence to verify its planetary nature.Keywords:
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We present a new analysis of the physical conditions in three Herbig-Haro complexes (HH 54, HH 212, and the L 1157 protostellar jet) using archival data from the Infrared Array Camera on the Spitzer Space Telescope. As described in detail in Paper I, the emission observed using the 4.5 μm filter is enhanced in molecular shocks (T = 1000–4000 K) at relatively high temperatures or densities compared with that observed with the 8.0 μm filter. Using these data sets, we investigate different distributions of gas between high and low temperatures/densities. Our analysis reveals the presence of a number of warm/dense knots, most of which appear to be associated with working surfaces such as the head of bow shocks and cometary features, and reverse shocks in the ejecta. These are distributed not only along the jet axis, as expected, but also across it. While some knotty or fragmenting structures can be explained by instabilities in shocked flows, others can be more simply explained by the scenario that the mass ejection source acts as a "shot gun," periodically ejecting bullets of material along similar but not identical trajectories. Such an explanation challenges to some degree the present paradigm for jet flows associated with low-mass protostars. It also gives clues to reconciling our understanding of the mass ejection mechanism in high- and low-mass protostars and evolved stars.
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We present 450, 850 μm and 1300 μm images of regions with embedded candidate protostars. Some of them are associated with HH objects (HH 7-11, HH 1-2, HH 147, HH 111, HH 108) and have been previously identified in the course of a 1300 μm survey. Other regions were taken from the IRAS PSC (04239+2436, 04368+2557, 20050+2720, 20386+6751, 22134+5834, 23011+6126). The new mm/submm images show the detailed structure of the regions some of which contain new compact sources as well as extended emission features. The inferred mm/submm fluxes are combined with IRAS data in order to derive the temperature of the associated dust, its mass and the re-radiated luminosity. Taking the ratio of FIR-to-submm luminosity as an indicator for the evolutionary stage, we find that 15 out of 17 sources have , indicating that most objects are probably genuine protostars. For the first time, we detect dust emission associated with HH objects themselves, H2 and CO flows which we interpret as density enhancements swept up by the ejected material.
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Abstract Characterization of how dense molecular cores evolve into stars has historically been made through observational changes in their 2 to 25 μm spectral energy distribution (SED) or bolometric temperature via the Class system. Linking these observational classes to a physical protostellar phase or Stages in a consistent manner remains challenging. In order to provide a uniform indicator of whether an observationally classified embedded protostar candidate is likely to be a physical phase Stage 0 or I protostar, we performed an HCO + ( J =3-2) survey of Class 0+I and Flat SED young stellar objects (YSOs) in the Spitzer nearby (D < 500 pc) Gould Belt cloud surveys. We use criteria from van Kempen et al .(2009) to classify sources as Stage 0+I or bona fide protostars and find 84% of our HCO + detected sources meet that criteria. We recommend 0.54 Myr as an evolutionary timescale for these embedded protostars. We discuss trends in our sample with spatial distribution, molecular cloud extinction, spectral index, and bolometric temperature and luminosity.
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Massive protostars are generally enshrouded in dust, so that most of their radiation emerges in the far infrared. For protostars embedded in opaque, spherical cores, the spectral energy distribution (SED) is determined by two distance-independent parameters, the luminosity-to-mass ratio, is the radius of the core. Chakrabarti & McKee (2005a) have derived an approximate analytic expression for the SED that agrees well with numerical results. It is generally not possible to infer the power-law of the density from the SED of a massive protostar. Masses and accretion rates are inferred for several well-studied sources.
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view Abstract Citations (73) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectral Energy of First Protostellar Cores: Detecting ``Class -I'' Protostars with ISO and SIRTF Boss, Alan P. ; Yorke, Harold W. Abstract Radiative hydrodynamical models of protostellar collapse are used to calculate the spectral energy distributions of single and binary protostars at the phase of formation of the first (outer) protostellar core. In accordance with the established nomenclature, where classes 0, I, II, and III form a sequence in time, we term these pre-class 0 objects to be class-I ('class minus one') objects. These class -I objects are characterized by central core temperatures of approximately 200 K, envelope temperatures of approximately 10 K, and substantial far-infrared and submillimeter-wave fluxes. While undetectable by IRAS, these objects should be detectable by Infrared Space Observatory (ISO) and Space Infrared Telescope Facility (SITF) at 60 micrometer and longer wavelengths. First protostellar cores exist for times on the order of a few percent of the total collapse time, implying that a small fraction of all protostellar objects should be class -I objects. Publication: The Astrophysical Journal Pub Date: February 1995 DOI: 10.1086/187743 Bibcode: 1995ApJ...439L..55B Keywords: Far Infrared Radiation; Hydrodynamic Equations; Mathematical Models; Protostars; Spectral Energy Distribution; Star Formation; Stellar Cores; Computerized Simulation; Infrared Astronomy; Infrared Astronomy Satellite; Infrared Space Observatory (Iso); Space Infrared Telescope Facility; Astrophysics; INFRARED: STARS; STARS: FORMATION; STARS: PRE--MAIN-SEQUENCE full text sources ADS | data products SIMBAD (1)
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We report the discovery of an extremely red object embedded in the massive SCUBA core JCMT 18354-0649S. This object is not associated with any known radio or far-IR source, though it appears in Spitzer IRAC data obtained as part of the GLIMPSE survey. At shorter wavelengths, this embedded source exhibits an extreme color, K − L' = 6.7. At an assumed distance of 5.7 kpc, this source has a near-IR luminosity of ∼1000 L☉. Its spectral energy distribution (SED) rises sharply from 2.1 μm to 8 μm, similar to that of a Class 0 young stellar object. Theoretical modeling of the SED indicates that the central star has a mass of 6–12 M☉, with an optical extinction of more than 30. As both inflow and outflow motions are present in JCMT 18354-0649S, we suggest that this deeply embedded source is (1) a massive protostar in the early stages of accretion, and (2) the driving source of a massive molecular outflow evident in HCN J = 3–2 profiles observed toward this region.
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The region south of the reflection nebula NGC1333 in Perseus is an active star forming region including numerous Herbig-Haro objects and at least 5 protostar candidates with molecular outflows and far-infrared emission. It has been actively studied in various wave bands (e.g. Aspin et al 1994 and references therein). We observed this region with ASCA with the primary objective to detect X-rays from the protostars embedded deep in the molecular cloud.
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view Abstract Citations (39) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The spectrum of Herbig-Haro object No. 1. Böhm, K. -H. ; Perry, J. F. ; Schwartz, R. Abstract A spectroscopic and spectrophotometric study of Herbig-Haro Object No. 1 has been carried out using four image-tube spectra covering the spectral range 3700 A < A <% 6850 A. New line identifications include additional [Fe ii] and [N ii] lines as well as the Balmer lines HlO, Hl1, and Hl2. Paying special attention to the complicated behavior of the dispersion curve on image-tube plates, we derive a preliminary radial velocity of - 15 i 7 km 1 for the inner parts of HerbigHaro No. 1. The surrounding gas at a distance of about 10" from the center (radiating only in [0 ii] A3727 and the Balmer lines) has a radial velocity of approximately 0 km 1 The line intensities show a "change" in comparison to earlier measurements of typically 15-30 percent. These differences can be attributed either to systematic errors in the two spectrophotometric studies or to a real time change (corresponding to the changes observed by Herbig on direct photographs) during the last 15 years from T, 7500' to T, 10,000' K and from N, 1.3 x 10 to N, 2 x 10 in the inner regions of Herbig-Haro No. 1. The line ratio [S ii] 6717/6731 indicates N, 9.0 x 10 , and the ratio [0 ii] 3726/3729 shows N, 2.4 x 10 in the regions of formation of these lines. The abundance ratio S/Ne/O is 0.1/ 0.6/1.0, in fair agreement with planetary nebulae abundances. The Balmer decrement agrees well with newer calculations for Menzel's case B. There is no indication that the Balmer lines (with half-widths less than 1 A) are broader than the other emission lines. We argue that these two facts may not be compatible with the recently proposed hypothesis that the excitation is due to fast protons. Subject headings: nebulae - spectrophotometry - star formation Publication: The Astrophysical Journal Pub Date: January 1973 DOI: 10.1086/151855 Bibcode: 1973ApJ...179..149B full text sources ADS | data products SIMBAD (3)
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We point out that protoplanets created in the framework of the tidal downsizing (TD) theory for planet formation play a very important role for the evolution of accretion discs hosting them. Since all TD protoplanets are initially as massive as ∼10MJ, they are able to open very deep gaps in their discs, and even completely isolate the inner disc flows from the outer ones. Furthermore, in contrast to other planet formation theories, TD protoplanets are mass donors for their protostars. One potentially observable signature of planets being devoured by their protostars are FU Ori like outbursts, and episodic protostar accretion more generally, as discussed by a number of authors recently. Here, we explore another observational implication of the TD hypothesis: dust poor inner accretion flows, which we believe may be relevant to some of the observed millimetre-bright transitional discs around protostars. In our model, a massive protoplanet interrupts the flow of the outer dust-rich disc on its protostar, and at the same time loses a part of its dust-poor envelope into the inner disc. This then powers the observed gas-but-no-dust accretion on to the star. Upon a more detailed investigation, we find that this scenario is quite natural for young massive discs but is less so for older discs, e.g., those whose self-gravitating phase has terminated a fraction of a Myr or more ago. This stems from the fact that TD protoplanets of such an age should have contracted significantly, and so are unlikely to lose much mass. Therefore, we conclude that either (i) the population of ‘transition discs’ with large holes and dust-poor accretion is much younger than generally believed, or (ii) there is a poorly understood stage for late removal of dust-poor envelopes from TD planets; (iii) another explanation for the observations is correct.
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