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Sample records for low-mass protostar b1-b

  1. A Cold Complex Chemistry Toward the Low-mass Protostar B1-b: Evidence for Complex Molecule Production in Ices

    NASA Astrophysics Data System (ADS)

    Öberg, Karin I.; Bottinelli, Sandrine; Jørgensen, Jes K.; van Dishoeck, Ewine F.

    2010-06-01

    Gas-phase complex organic molecules have been detected toward a range of high- and low-mass star-forming regions at abundances which cannot be explained by any known gas-phase chemistry. Recent laboratory experiments show that UV irradiation of CH3OH-rich ices may be an important mechanism for producing complex molecules and releasing them into the gas phase. To test this ice formation scenario, we mapped the B1-b dust core and nearby protostar in CH3OH gas using the IRAM 30 m telescope to identify locations of efficient non-thermal ice desorption. We find three CH3OH abundance peaks tracing two outflows and a quiescent region on the side of the core facing the protostar. The CH3OH gas has a rotational temperature of ~10 K at all locations. The quiescent CH3OH abundance peak and one outflow position were searched for complex molecules. Narrow, 0.6-0.8 km s-1 wide, HCOOCH3 and CH3CHO lines originating in cold gas are clearly detected, CH3OCH3 is tentatively detected, and C2H5OH and HOCH2CHO are undetected toward the quiescent core, while no complex molecular lines were found toward the outflow. The core abundances with respect to CH3OH are ~2.3% and 1.1% for HCOOCH3 and CH3CHO, respectively, and the upper limits are 0.7%-1.1%, which is similar to most other low-mass sources. The observed complex molecule characteristics toward B1-b and the pre-dominance of HCO-bearing species suggests a cold ice (below 25 K, the sublimation temperature of CO) formation pathway followed by non-thermal desorption through, e.g., UV photons traveling through outflow cavities. The observed complex gas composition together with the lack of any evidence of warm gas-phase chemistry provides clear evidence of efficient complex molecule formation in cold interstellar ices. Based on observations carried out with the IRAM 30 m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).

  2. Winds from Low Mass Protostars

    NASA Astrophysics Data System (ADS)

    Shu, Frank H.; Lizano, Susana; Adams, Fred C.; Ruden, Steven P.

    In its last stages, star formation in molecular clouds includes the onset of a stellar wind that helps to clear away the surrounding placenta of gas and dust, thereby making the young stellar object optically visible. The authors discuss new observational evidence that the emerging wind is largely neutral and atomic in low-mass protostars. They then suggest a simple theoretical mechanism for the generation of such powerful neutral winds.

  3. Deuterated water in low-mass protostars

    NASA Astrophysics Data System (ADS)

    Coutens, Audrey; Vastel, Charlotte; Chess Collaboration; Wish Collaboration; Hexos Collaboration

    2013-07-01

    In addition to its dominant role in the cooling of warm gas and in the oxygen chemistry, water is a primordial species in the emergence of life, and comets may have brought a large fraction to Earth to form the oceans. Observations of deuterated water are an important complement for studies of H2O to understand how water forms and how it has evolved from cold prestellar cores to protoplanetary disks and consequently oceans for the Earth's specific, but probably not isolated, case. Several deuterated water transitions were observed with the Herschel/HIFI (Heterodyne Instrument for Far Infrared) instrument towards three low-mass protostars: IRAS 16293-2422, NGC1333 IRAS4A and NGC1333 IRAS4B. In the first source, both HDO and D2O lines are detected, thanks to the unbiased spectral survey carried out by the CHESS key program (Vastel et al. 2010, Coutens et al. 2013a). In the framework of a collaboration between the CHESS, WISH and HEXOS programs, two HDO key lines were observed towards the two other protostars. In addition, complementary observations were carried out with several ground-based single-dish telescopes (IRAM-30m, JCMT, APEX). We used the non-LTE RATRAN spherical model (Hogerheijde & van der Tak 2000) to determine the HDO abundance distribution throughout the protostellar envelope. An abundance jump at 100 K is required to reproduce the line profiles. Indeed, water molecules trapped in the icy grain mantles thermally desorb in the hot corinos, the inner warm regions of the protostellar envelopes. We also obtain that it is necessary to add a water-rich external absorbing layer to reproduce the absorbing components of the HDO and D2O fundamental transitions in all sources (Coutens et al. 2012, 2013a,b). The results derived for the different sources will be then presented and discussed.

  4. COMPLEX MOLECULES TOWARD LOW-MASS PROTOSTARS: THE SERPENS CORE

    SciTech Connect

    Oeberg, Karin I.; Van der Marel, Nienke; Kristensen, Lars E.; Van Dishoeck, Ewine F.

    2011-10-10

    Gas-phase complex organic molecules are commonly detected toward high-mass protostellar hot cores. Detections toward low-mass protostars and outflows are comparatively rare, and a larger sample is the key to investigate how the chemistry responds to its environment. Guided by the prediction that complex organic molecules form in CH{sub 3}OH-rich ices and thermally or non-thermally evaporate with CH{sub 3}OH, we have identified three sight lines in the Serpens core-SMM1, SMM4, and SMM4-W-which are likely to be rich in complex organics. Using the IRAM 30 m telescope, narrow lines (FWHM of 1-2 km s{sup -1}) of CH{sub 3}CHO and CH{sub 3}OCH{sub 3} are detected toward all sources, HCOOCH{sub 3} toward SMM1 and SMM4-W, and C{sub 2}H{sub 5}OH not at all. Beam-averaged abundances of individual complex organics range between 0.6% and 10% with respect to CH{sub 3}OH when the CH{sub 3}OH rotational temperature is applied. The summed complex organic abundances also vary by an order of magnitude, with the richest chemistry toward the most luminous protostar SMM1. The range of abundances compare well with other beam-averaged observations of low-mass sources. Complex organic abundances are of the same order of magnitude toward low-mass protostars and high-mass hot cores, but HCOOCH{sub 3} is relatively more important toward low-mass protostars. This is consistent with a sequential ice photochemistry, dominated by CHO-containing products at low temperatures and early times.

  5. Water D/H Ratio In Low-Mass Protostars

    NASA Astrophysics Data System (ADS)

    Persson, Magnus V.; Jørgensen, Jes K.; van Dishoeck, Ewine F.; Harsono, Daniel

    2013-07-01

    Water is an important molecule for our life on Earth, but its way from formation on the surfaces of dust grains to planets and the accompanying chemical processing are not well understood. Through evaporation in the warm inner regions of protostars, water brings complex organics and other species previously locked up in the ice into the gas phase. The water deuterium fractionation (HDO/H2O abundance ratio) has traditionally been used to infer the amount of water that was brought to the Earth by comets. Deducing this ratio in the warm gas of deeply-embedded low-mass protostars allows to extend the discussion of the origin of Earth's water to earlier evolutionary stages. This poster present high-angular resolution, ground based interferometric observations of both HDO and H2(18)O water isotopologues toward several Class~0 low-mass protostars. The emission is compact, and stems from the inner few 100 AU in all sources. The derived amount of deuterium fractionation in water, obtained assuming LTE and optically thin emission, is the same within the uncertainties in all sources and shows only small enhancements compared with Earth's oceans and solar system's comets.

  6. Chemical tracers of episodic accretion in low-mass protostars

    NASA Astrophysics Data System (ADS)

    Visser, Ruud; Bergin, Edwin A.; Jørgensen, Jes K.

    2015-05-01

    Aims: Accretion rates in low-mass protostars can be highly variable in time. Each accretion burst is accompanied by a temporary increase in luminosity, heating up the circumstellar envelope and altering the chemical composition of the gas and dust. This paper aims to study such chemical effects and discusses the feasibility of using molecular spectroscopy as a tracer of episodic accretion rates and timescales. Methods: We simulate a strong accretion burst in a diverse sample of 25 spherical envelope models by increasing the luminosity to 100 times the observed value. Using a comprehensive gas-grain network, we follow the chemical evolution during the burst and for up to 105 yr after the system returns to quiescence. The resulting abundance profiles are fed into a line radiative transfer code to simulate rotational spectra of C18O, HCO+, H13CO+, and N2H+ at a series of time steps. We compare these spectra to observations taken from the literature and to previously unpublished data of HCO+ and N2H+ 6-5 from the Herschel Space Observatory. Results: The bursts are strong enough to evaporate CO throughout the envelope, which in turn enhances the abundance of HCO+ and reduces that of N2H+. After the burst, it takes 103-104 yr for CO to refreeze and for HCO+ and N2H+ to return to normal. The H2O snowline expands outwards by a factor of ~10 during the burst; afterwards, it contracts again on a timescale of 102-103 yr. The chemical effects of the burst remain visible in the rotational spectra for as long as 105 yr after the burst has ended, highlighting the importance of considering luminosity variations when analyzing molecular line observations in protostars. The spherical models are currently not accurate enough to derive robust timescales from single-dish observations. As follow-up work, we suggest that the models be calibrated against spatially resolved observations in order to identify the best tracers to be used for statistically significant source samples. Herschel

  7. Modelling water in the envelopes of low-mass protostars

    NASA Astrophysics Data System (ADS)

    van Kempen, Tim A.; Jørgensen, Jes K.; Hogerheijde, Michiel R.; van Dishoeck, Ewine F.

    Using sophisticated spherically symmetric radiative transfer models for gas and dust, we simulate the emission of H2O and its isotopes for the circumstellar envelopes around class 0 protostars, as preparatory science for the ESA cornerstone mission Herschel and its spectrometer, HIFI. L483mm is taken as an example. We probe a wide range of models in which dust, freeze-out and a large variety of abundance structures and optical depths are taken into account. A sample of water lines is selected that are observable by Herschel. Expected fluxes for these lines are derived from the models, convolved with the Herschel beam size. 1. Introduction Water has been detected by the LWS instruments aboard ISO in low-mass protostars (e.g. Ceccarelli et al. 1999, Giannini et al. 2001). The origin of the water lines is still subject of discussion, however. It has been theorized to originate in both the outflow and the quiescent infalling envelope. Ceccarelli et al. (1999) place the water in the small (200 AU), dense (> 107cm-3) and warm (> 100 K) region of the protostellar envelope. The ESA Herschel mission and in particular the HIFI instrument are particularly well suited to observe rotational far-infrared and submillimeter water lines in these environments and test the various models. 2. Approach We started with the physical structure deduced by Jørgensen (2004) for L483mm (Lbol = 9Lsol, Menv10K = 4.4Msol, D=200 pc), giving the density and temperature profiles for a typical protostellar envelope. These profiles are the result of a dust radiative transfer calculation with DUSTY (Ivezic & Elitzur, 1997). The line radiative transfer is subsequently calculated through RATRAN, developed by Hogerheijde & van der Tak (2000). The dust to gas ratio has been set at 1:100, the dust opacities are approximated by the OH5 (Ossenkopf & Henning 1994) at a density of 106cm-3. To simulate the abundance of the water molecule, we have used trial abundances with the assumption that water freezes out

  8. A Complex Organic Slushy Bathing Low-Mass Protostars

    NASA Astrophysics Data System (ADS)

    Drozdovskaya, Maria; Walsh, Catherine; Visser, Ruud; Harsono, Daniel; van Dishoeck, Ewine

    2015-08-01

    Complex organic molecules are ubiquitous companions of young forming stars. They were first observed in hot cores surrounding high-mass protostars [e.g., 1], but have since also been detected in the environs of several low-mass counterparts [e.g., 2]. Recent studies have shown that colder envelopes and positions with impinging outflows may also glow with emission from complex organic species [e.g., 3, 4]. For this meeting, I would like to present physicochemical modeling results on the synthesis of complex organics in an envelope-cavity system that is subject to non-thermal processing. This includes wavelength-dependent radiative transfer calculations with RADMC [5] and a comprehensive gas-grain chemical network [6]. The results show that the morphology of such a system delineates three distinct regions: the cavity wall layer with time-dependent and species-variant enhancements; a torus rich in complex organic ices, but not reflected in gas-phase abundances; and the remaining outer envelope abundant in simpler solid and gaseous molecules. Within the adopted paradigm, complex organic molecules are demonstrated to have unique lifetimes and be grouped into early and late species [7]. Key chemical processes for forming and destroying complex organic molecules will be discussed. In addition, the results of adding newly experimentally verified routes [8] into the existing chemical networks will be shown.[1] Blake G. A., Sutton E. C., Masson C. R., Phillips T. G., 1987, ApJ, 315, 621[2] Jørgensen J. K., Favre C., Bisschop S. E., Bourke T. L., van Dishoeck E. F., Schmalzl M., 2012, ApJ, 757, L4[3] Arce H. G., Santiago-García J., Jørgensen J. K., Tafalla M., Bachiller R., 2008, ApJ, 681, L21[4] Öberg K. I., Bottinelli S., Jørgensen J. K., van Dishoeck E. F., 2010, ApJ, 716, 825[5] Dullemond C. P., Dominik C., 2004, A&A, 417, 159[6] Walsh C., Millar T. J., Nomura H., Herbst E., Widicus Weaver S., Aikawa Y., Laas J. C., Vasyunin A. I., 2014, A&A, 563, A33[7] Drozdovskaya

  9. Heavy water stratification in a low-mass protostar

    NASA Astrophysics Data System (ADS)

    Coutens, A.; Vastel, C.; Cazaux, S.; Bottinelli, S.; Caux, E.; Ceccarelli, C.; Demyk, K.; Taquet, V.; Wakelam, V.

    2013-05-01

    Context. Despite the low elemental deuterium abundance in the Galaxy, enhanced molecular deuterium fractionation has been found in the environments of low-mass star-forming regions and, in particular, the Class 0 protostar IRAS 16293-2422. Aims: The key program Chemical HErschel Surveys of Star forming regions (CHESS) aims at studying the molecular complexity of the interstellar medium. The high sensitivity and spectral resolution of the Herschel/HIFI (Heterodyne Instrument for Far-Infrared) instrument provide a unique opportunity to observe the fundamental 11,1-00,0 transition of ortho-D2O at 607 GHz and the higher energy 21,2-10,1 transition of para-D2O at 898 GHz, both of which are inaccessible from the ground. Methods: The ortho-D2O transition at 607 GHz was previously detected. We present in this paper the first tentative detection for the para-D2O transition at 898 GHz. The spherical Monte Carlo radiative transfer code RATRAN was used to reproduce the observed line profiles of D2O with the same method that was used to reproduce the HDO and H218O line profiles in IRAS 16293-2422. Results: As for HDO, the absorption component seen on the D2O lines can only be reproduced by adding an external absorbing layer, possibly created by the photodesorption of the ices at the edges of the molecular cloud. The D2O column density is found to be about 2.5 × 1012 cm-2 in this added layer, leading to a D2O/H2O ratio of about 0.5%. At a 3σ uncertainty, upper limits of 0.03% and 0.2% are obtained for this ratio in the hot corino and the colder envelope of IRAS 16293-2422, respectively. Conclusions: The deuterium fractionation derived in our study suggests that the ices present in IRAS 16293-2422 formed on warm dust grains (~15-20 K) in dense (~104-5 × 104 cm-3) translucent clouds. These results allow us to address the earliest phases of star formation and the conditions in which ices form. Based on Herschel/HIFI observations. Herschel is an ESA space observatory with

  10. Infrared Observations of Hot Gas and Cold Ice Toward the Low Mass Protostar Elias 29

    NASA Technical Reports Server (NTRS)

    Boogert, A. C. A.; Tielens, A. G. G. M.; Ceccarelli, C.; Boonman, A. M. S.; vanDishoeck, E. F.; Keane, J. V.; Whittet, D. C. B.; deGraauw, T.

    2000-01-01

    We have obtained the full 1-200 micrometer spectrum of the low luminosity (36 solar luminosity Class I protostar Elias 29 in the rho Ophiuchi molecular cloud. It provides a unique opportunity to study the origin and evolution of interstellar ice and the interrelationship of interstellar ice and hot core gases around low mass protostars. We see abundant hot CO and H2O gas, as well as the absorption bands of CO, CO2, H2O and "6.85 micrometer" ices. We compare the abundances and physical conditions of the gas and ices toward Elias 29 with the conditions around several well studied luminous, high mass protostars. The high gas temperature and gas/solid ratios resemble those of relatively evolved high mass objects (e.g. GL 2591). However, none of the ice band profiles shows evidence for significant thermal processing, and in this respect Elias 29 resembles the least evolved luminous protostars, such as NGC 7538 : IRS9. Thus we conclude that the heating of the envelope of the low mass object Elias 29 is qualitatively different from that of high mass protostars. This is possibly related to a different density gradient of the envelope or shielding of the ices in a circumstellar disk. This result is important for our understanding of the evolution of interstellar ices, and their relation to cometary ices.

  11. Observations of Carbon Chain Chemistry in the Envelopes of Low-Mass Protostars

    NASA Technical Reports Server (NTRS)

    Cordiner, M.; Charnley, S.; Buckle, J. V.; Walsh, C.; Millar, T. J.

    2012-01-01

    Observational results are reported from our surveys in the Northern Hemisphere (using the Onsala 20 m telescope) and the Southern Hemisphere (using the Mopra 22 m telescope) to search for 3 mm emission lines from carbon-chain-bearing species and other complex molecules in the envelopes of low-mass protostars. Based on a sample of approximately 60 sources, we find that carbon-chain-bearing species including HC3N (and C4H) are highly abundant in the vicinity of more than half of the observed protostars. The origin and evolution of these species, including their likely incorporation into ices in protoplanetary disks will be discussed

  12. From nearby low-mass protostars to high redshift starbursts: protostellar outflows tracing the IMF

    NASA Astrophysics Data System (ADS)

    Kristensen, Lars E.; Bergin, Edwin

    2015-08-01

    Embedded low-mass protostars are notoriously difficult to observe even in the nearest Galactic high-mass clusters where they outnumber the high-mass protostars by orders of magnitude. Thus, without a good tracer of the low-mass population, we do not have a good handle on the shape of the initial (core) mass function, leaving little hope for extrapolating to extragalactic regions where we will never have neither the sensitivity nor the resolution to directly observe this population. A good tracer of the low-mass population is needed.One such physical tracer is outflows. Outflow emission is directly proportional to envelope mass, and outflows are predominantly active during the deeply embedded phases of star formation. What is required for this method to work is species and transitions tracing outflows uniquely such that any signal is not diluted by the surrounding cloud, such as certain methanol transitions, water, high-J CO (J > 10).I will present a statistical model of a forming high-mass cluster. The model includes what we currently know about Galactic high-mass clusters and incorporates outflow emission from low-mass protostars. The latter component is obtained from observations of tens of nearby embedded low-mass protostellar outflows in the above-mentioned tracers. The model is benchmarked against ALMA and Herschel-HIFI observations of Galactic clusters proving the concept, and preliminary extrapolations to the extragalactic regime are presented. With this new probe, and traditional probes of the distant star formation which predominantly trace high mass stars, we will be able to explore the IMF in starburst galaxies from low to high redshift.

  13. Water in embedded low-mass protostars: cold envelopes and warm outflows

    NASA Astrophysics Data System (ADS)

    Kristensen, Lars E.; van Dishoeck, Ewine; Mottram, Joseph; Schmalzl, Markus; Visser, Ruud

    2015-08-01

    As stars form, gas from the parental cloud is transported through the molecular envelope to the protostellar disk from which planets eventually form. Water plays a crucial role in such systems: it forms the backbone of the oxygen chemistry, it is a unique probe of warm and hot gas, and it provides a unique link between the grain surface and gas-phase chemistries. The distribution of water, both as ice and gas, is a fundamental question to our understanding of how planetary systems, such as the Solar System, form.The Herschel Space Observatory observed many tens of embedded low-mass protostars in a suite of gas-phase water transitions in several programs (e.g. Water in Star-forming regions with Herschel, WISH, and the William Herschel Line Legacy Survey, WILL), and related species (e.g. CO in Protostars with HIFI, COPS-HIFI). I will summarize what Herschel has revealed about the water distribution in the cold outer molecular envelope of low-mass protostars, and the warm gas in outflows, the two components predominantly traced by Herschel observations. I will present our current understanding of where the water vapor is in protostellar systems and the underlying physical and chemical processes leading to this distribution. Through these dedicated observational surveys and complementary modeling efforts, we are now at a stage where we can quantify where the water is during the early stages of star formation.

  14. Study of deuterated water in the low-mass protostar IRAS16293-2422

    NASA Astrophysics Data System (ADS)

    Coutens, A.; Vastel, C.; Caux, E.; Ceccarelli, C.; Herschel Chess Team

    2011-05-01

    Observations of deuterated water are an important complement for studies of H2O, since they give strong constraints on the formation processes: grain surfaces versus gas-phase chemistry through energetic process as shocks. The CHESS (Chemical HErschel Surveys of Star forming regions) Key Program has allowed to detect a lot of transitions of HDO (8) and H2O (16) as well as its isotopes H_218O and H_217O towards the low-mass protostar IRAS16293-2422 thanks to the unbiaised spectral survey carried out with the HIFI instrument on board the Herschel Space Observatory. Complementary data of HDO from the ground-based telescopes IRAM and JCMT are also available, allowing a precise determination of the abundance of deuterated water through the protostar envelope. In order to reproduce the observed line profiles, we have performed a modeling of HDO from the hot corino through the envelope using the physical structure of the protostar (Crimier et al. 2010) and the spherical Monte Carlo radiative transfer code RATRAN, which takes also into account radiative pumping by continuum emission from dust. We have used new HDO collision rates with H_2, recently computed by Wiesenfeld, Scribano and Faure (2011, PCCP). The same method has been applied to model H_2O and its isotopes H_218O and H_217O. We will present the results of this analysis and discuss the determined abundances.

  15. Probing the effects of external irradiation on low-mass protostars through unbiased line surveys

    NASA Astrophysics Data System (ADS)

    Lindberg, J. E.; Jørgensen, J. K.; Watanabe, Y.; Bisschop, S. E.; Sakai, N.; Yamamoto, S.

    2015-12-01

    Context. The envelopes of molecular gas around embedded low-mass protostars show different chemistries, which can be used to trace their formation history and physical conditions. The excitation conditions of some molecular species can also be used to trace these physical conditions, making it possible to constrain for instance sources of heating and excitation. Aims: We study the range of influence of an intermediate-mass Herbig Be protostar. We also study the effect of feedback from the environment on the chemical and physical properties of embedded protostars. Methods: We followed up on an earlier line survey of the Class 0/I source R CrA IRS7B in the 0.8 mm window with an unbiased line survey of the same source in the 1.3 mm window using the Atacama Pathfinder Experiment (APEX) telescope. We also studied the excitation of the key species H2CO, CH3OH, and c-C3H2 in a complete sample of the 18 embedded protostars in the Corona Australis star-forming region. Radiative transfer models were employed to establish abundances of the molecular species. Results: We detect line emission from 20 molecular species (32 including isotopologues) in the two surveys. The most complex species detected are CH3OH, CH3CCH, CH3CHO, and CH3CN (the latter two are only tentatively detected). CH3CN and several other complex organic molecules are significantly under-abundant in comparison with what is found towards hot corino protostars. The H2CO rotational temperatures of the sources in the region decrease with the distance to the Herbig Be star R CrA, whereas the c-C3H2 temperatures remain constant across the star-forming region. Conclusions: The high H2CO temperatures observed towards objects close to R CrA suggest that this star has a sphere of influence of several 10 000 AU in which it increases the temperature of the molecular gas to 30-50 K through irradiation. The chemistry in the IRS7B envelope differs significantly from many other embedded protostars, which could be an effect of

  16. The Evolution of Matter in the Embedded Stages of Low-Mass Protostars

    NASA Astrophysics Data System (ADS)

    Jorgensen, Jes; Lommen, D.; Bourke, T. L.; van Dishoeck, E. F.; Wilner, D.; PROSAC Team

    2008-03-01

    One of the most important questions about low-mass star formation is how circumstellar disks form and evolve through the embedded protostellar stages. We present the results of high angular resolution (1-2"; 200-400 AU) observations from a large program, PROSAC, studying embedded low-mass protostars (Class 0 and I objects) with the Submillimeter Array. In total 17 sources have been observed in a variety of lines of common molecular species together with continuum at (sub)millimeter wavelengths. The continuum observations reveal the presence of compact emission on the smallest scales in all sources which can best be attributed to thermal emission from dust in the circumstellar disks. The inferred masses of the central disks are comparable for both Class 0 and I objects suggesting that disks are formed and rapidly grow in size early in the evolution of the protostars. Line observations of the more evolved Class I systems reveal rotational signatures which in turn constrain the central stellar masses. Together with single-dish continuum data, these observations for the first time allow us to trace evolution of the mass of the stars, disks and envelopes through these pivotal stages.

  17. Subarcsecond resolution observations of warm water toward three deeply embedded low-mass protostars

    NASA Astrophysics Data System (ADS)

    Persson, M. V.; Jørgensen, J. K.; van Dishoeck, E. F.

    2012-05-01

    Context. Water is present during all stages of star formation: as ice in the cold outer parts of protostellar envelopes and dense inner regions of circumstellar disks, and as gas in the envelopes close to the protostars, in the upper layers of circumstellar disks and in regions of powerful outflows and shocks. Because of its key importance in the understanding of its origin in our own solar system, following the evolution of water all the way to the planet-forming disk is a fundamental task in research in star formation and astrochemistry. Aims: In this paper we probe the mechanism regulating the warm gas-phase water abundance in the innermost hundred AU of deeply embedded (Class 0) low-mass protostars, and investigate its chemical relationship to other molecular species during these stages. Methods: Millimeter wavelength thermal emission from the para-H218O 31,3 - 22,0 (Eu = 203.7 K) line was imaged at high angular resolution (0.75 arcsec; 190 AU) with the IRAM Plateau de Bure Interferometer toward the deeply embedded low-mass protostars NGC 1333-IRAS2A and NGC 1333-IRAS4A. Results: Compact H218O emission is detected toward IRAS2A and one of the components in the IRAS4A binary; in addition CH3OCH3, C2H5CN, and SO2 are detected. Extended water emission is seen toward IRAS2A, possibly associated with the outflow. Conclusions: The results complement a previous detection of the same transition toward NGC 1333-IRAS4B. The detections in all systems suggests that the presence of water on ≲ 100 AU scales is a common phenomenon in embedded protostars and that the non-detections of hot water with Spitzer toward the two systems studied in this paper are likely due to geometry and high extinction at mid-infrared wavelengths. We present a scenario in which the origin of the emission from warm water is in a flattened disk-like structure dominated by inward motions rather than rotation. The gas-phase water abundance varies between the sources, but is generally much lower than

  18. Water deuterium fractionation in the low-mass protostar NGC1333-IRAS2A

    NASA Astrophysics Data System (ADS)

    Liu, F.-C.; Parise, B.; Kristensen, L.; Visser, R.; van Dishoeck, E. F.; Güsten, R.

    2011-03-01

    Context. Although deuterium enrichment of water may provide an essential piece of information in the understanding of the formation of comets and protoplanetary systems, only a few studies up to now have aimed at deriving the HDO/H2O ratio in low-mass star forming regions. Previous studies of the molecular deuteration toward the solar-type class 0 protostar, IRAS 16293-2422, have shown that the D/H ratio of water is significantly lower than other grain-surface-formed molecules. It is not clear if this property is general or particular to this source. Aims: In order to see if the results toward IRAS 16293-2422 are particular, we aimed at studying water deuterium fractionation in a second low-mass solar-type protostar, NGC1333-IRAS2A. Methods: Using the 1-D radiative transfer code RATRAN, we analyzed five HDO transitions observed with the IRAM 30 m, JCMT, and APEX telescopes. We assumed that the abundance profile of HDO in the envelope is a step function, with two different values in the inner warm (T > 100 K) and outer cold (T < 100 K) regions of the protostellar envelope. Results: The inner and outer abundance of HDO is found to be well constrained at the 3σ level. The obtained HDO inner and outer fractional abundances are xHDO_in = 6.6 × 10-8-1.0 × 10-7(3σ) and x^{HDO}out=9×10-11= 9 × 10-11-1.0-1.8 × 10-9(3σ). These values are close to those in IRAS 16293-2422, which suggests that HDO may be formed by the same mechanisms in these two solar-type protostars. Taking into account the (rather poorly onstrained) H2O abundance profile deduced from Herschel observations, the derived HDO/H2O in the inner envelope is ≥1% and in the outer envelope it is 0.9%-18%. These values are more than one order of magnitude higher than what is measured in comets. If the same ratios apply to the protosolar nebula, this would imply that there is some efficient reprocessing of the material between the protostellar and cometary phases. Conclusions: The H2O inner fractional

  19. Submillimeter-Wave Observations toward the Low-Mass Protostar IRAS 15398-3359 at Subarcsecond Resolution

    NASA Astrophysics Data System (ADS)

    Oya, Y.; Sakai, N.; Watanabe, Y.; Yamamoto, S.; Sakai, T.; Hirota, T.; Lindberg, J. E.; Bisschop, S. E.; Jørgensen, J. K.; van Dishoeck, E. F.

    2015-12-01

    Subarcsecond 0."5 images of H2CO and CCH line emission have been obtained in the 0.8 mm band toward the low-mass protostar IRAS 15398-3359 in the Lupus 1 cloud with ALMA. We have detected a compact component concentrated in the vicinity of the protostar and a well-collimated outflow cavity extending along the northeast-southwest axis. The inclination angle of the outflow is found to be almost edge-on (20°) based on the kinematic structure of the outflow cavity. The centrally concentrated component is interpreted by use of a model of the infalling rotating envelope with the estimated inclination angle, and the mass of the protostar is estimated to be less than 0.09 ⊙.

  20. Imaging chemical differentiation around the low-mass protostar L483-mm

    NASA Astrophysics Data System (ADS)

    Jørgensen, J. K.

    2004-09-01

    This paper presents a millimeter wavelength aperture-synthesis study of the spatial variations of the chemistry in the envelope around the deeply embedded low-mass protostar L483-mm on ˜1000 AU (5 arcsec) scales. Lines of 8 molecular species including CN, C18O, CS, C34S, HCN, H13CN, HCO+ and N2H+ have been observed using the Owens Valley Radio Observatory Millimeter Array. Continuum emission at 2.7-3.4 mm is well-fit by an envelope model based on previously reported submillimeter continuum images down to the sensitivity of the interferometer without introducing a disk/compact source, in contrast to what is seen for other protostellar objects. A velocity gradient in dense material close to the central protostar is traced by HCN, CS and N2H+, and is perpendicular to the large-scale CO outflow, with a pattern consistent with rotation around a ˜1 M⊙ central object. Velocity gradients in the propagation direction of the outflow suggest a clear interaction between the outflowing material and ``quiescent'' core. Significant differences are observed between the emission morphologies of various molecular species. The C18O interferometer observations are fit with a ``drop'' abundance profile where CO is frozen-out in a region of the envelope with temperatures lower than 40 K and densities higher than 1.5 × 105 cm-3, which is also required to reproduce previously reported single-dish observations. The N2H+ emission strongly resembles that of NH3 and is found to be absent toward the central continuum source. This is a direct consequence of the high CO abundances in the inner region as illustrated by a chemical model for the L483 envelope. The observed CN emission forms a spatial borderline between the outflowing and quiescent material probed by, respectively, HCO+ and N2H+, and also shows intermediate velocities compared to these two species. A scenario is suggested in which CN is enhanced in the walls of an outflow cavity due to the impact of UV irradiation either from

  1. The complex chemistry of outflow cavity walls exposed: the case of low-mass protostars

    NASA Astrophysics Data System (ADS)

    Drozdovskaya, Maria N.; Walsh, Catherine; Visser, Ruud; Harsono, Daniel; van Dishoeck, Ewine F.

    2015-08-01

    Complex organic molecules are ubiquitous companions of young low-mass protostars. Recent observations suggest that their emission stems, not only from the traditional hot corino, but also from offset positions. In this work, 2D physicochemical modelling of an envelope-cavity system is carried out. Wavelength-dependent radiative transfer calculations are performed and a comprehensive gas-grain chemical network is used to simulate the physical and chemical structure. The morphology of the system delineates three distinct regions: the cavity wall layer with time-dependent and species-variant enhancements; a torus rich in complex organic ices, but not reflected in gas-phase abundances and the remaining outer envelope abundant in simpler solid and gaseous molecules. Strongly irradiated regions, such as the cavity wall layer, are subject to frequent photodissociation in the solid phase. Subsequent recombination of the photoproducts leads to frequent reactive desorption, causing gas-phase enhancements of several orders of magnitude. This mechanism remains to be quantified with laboratory experiments. Direct photodesorption is found to be relatively inefficient. If radicals are not produced directly in the icy mantle, the formation of complex organics is impeded. For efficiency, a sufficient number of FUV photons needs to penetrate the envelope, and elevated cool dust temperatures need to enable grain-surface radical mobility. As a result, a high stellar luminosity and a sufficiently wide cavity favour chemical complexity. Furthermore within this paradigm, complex organics are demonstrated to have unique lifetimes and be grouped into early (formaldehyde, ketene, methanol, formic acid, methyl formate, acetic acid and glycolaldehyde) and late (acetaldehyde, dimethyl ether and ethanol) species.

  2. A study of deuterated water in the low-mass protostar IRAS 16293-2422

    NASA Astrophysics Data System (ADS)

    Coutens, A.; Vastel, C.; Caux, E.; Ceccarelli, C.; Bottinelli, S.; Wiesenfeld, L.; Faure, A.; Scribano, Y.; Kahane, C.

    2012-03-01

    Context. Water is a primordial species in the emergence of life, and comets may have brought a large fraction to Earth to form the oceans. To understand the evolution of water from the first stages of star formation to the formation of planets and comets, the HDO/H2O ratio is a powerful diagnostic. Aims: Our aim is to determine precisely the abundance distribution of HDO towards the low-mass protostar IRAS 16293-2422 and learn more about the water formation mechanisms by determining the HDO/H2O abundance ratio. Methods: A spectral survey of the source IRAS 16293-2422 was carried out in the framework of the CHESS (Chemical Herschel Surveys of Star forming regions) Herschel key program with the HIFI (Heterodyne Instrument for the Far-Infrared) instrument, allowing detection of numerous HDO lines. Other transitions have been observed previously with ground-based telescopes. The spherical Monte Carlo radiative transfer code RATRAN was used to reproduce the observed line profiles of HDO by assuming an abundance jump. To determine the H2O abundance throughout the envelope, a similar study was made of the H218O observed lines, as the H2O main isotope lines are contaminated by the outflows. Results: It is the first time that so many HDO and H218O transitions have been detected towards the same source with high spectral resolution. We derive an inner HDO abundance (T ≥ 100 K) of about 1.7 × 10-7 and an outer HDO abundance (T < 100 K) of about 8 × 10-11. To reproduce the HDO absorption lines observed at 894 and 465 GHz, it is necessary to add an absorbing layer in front of the envelope. It may correspond to a water-rich layer created by the photodesorption of the ices at the edges of the molecular cloud. At a 3σ uncertainty, the HDO/H2O ratio is 1.4-5.8% in the hot corino, whereas it is 0.2-2.2% in the outer envelope. It is estimated at ~4.8% in the added absorbing layer. Conclusions: Although it is clearly higher than the cosmic D/H abundance, the HDO/H2O ratio remains

  3. Shockingly low water abundances in Herschel/PACS observations of low-mass protostars in Perseus

    NASA Astrophysics Data System (ADS)

    Karska, A.; Kristensen, L. E.; van Dishoeck, E. F.; Drozdovskaya, M. N.; Mottram, J. C.; Herczeg, G. J.; Bruderer, S.; Cabrit, S.; Evans, N. J.; Fedele, D.; Gusdorf, A.; Jørgensen, J. K.; Kaufman, M. J.; Melnick, G. J.; Neufeld, D. A.; Nisini, B.; Santangelo, G.; Tafalla, M.; Wampfler, S. F.

    2014-12-01

    Context. Protostars interact with their surroundings through jets and winds impinging on the envelope and creating shocks, but the nature of these shocks is still poorly understood. Aims: Our aim is to survey far-infrared molecular line emission from a uniform and significant sample of deeply-embedded low-mass young stellar objects (YSOs) in order to characterize shocks and the possible role of ultraviolet radiation in the immediate protostellar environment. Methods: Herschel/PACS spectral maps of 22 objects in the Perseus molecular cloud were obtained as part of the William Herschel Line Legacy (WILL) survey. Line emission from H2O, CO, and OH is tested against shock models from the literature. Results: Observed line ratios are remarkably similar and do not show variations with physical parameters of the sources (luminosity, envelope mass). Most ratios are also comparable to those found at off-source outflow positions. Observations show good agreement with the shock models when line ratios of the same species are compared. Ratios of various H2O lines provide a particularly good diagnostic of pre-shock gas densities, nH ~ 105 cm-3, in agreement with typical densities obtained from observations of the post-shock gas when a compression factor on the order of 10 is applied (for non-dissociative shocks). The corresponding shock velocities, obtained from comparison with CO line ratios, are above 20 km s-1. However, the observations consistently show H2O-to-CO and H2O-to-OH line ratios that are one to two orders of magnitude lower than predicted by the existing shock models. Conclusions: The overestimated model H2O fluxes are most likely caused by an overabundance of H2O in the models since the excitation is well-reproduced. Illumination of the shocked material by ultraviolet photons produced either in the star-disk system or, more locally, in the shock, would decrease the H2O abundances and reconcile the models with observations. Detections of hot H2O and strong OH

  4. High-J CO survey of low-mass protostars observed with Herschel-HIFI

    NASA Astrophysics Data System (ADS)

    Yıldız, U. A.; Kristensen, L. E.; van Dishoeck, E. F.; San José-García, I.; Karska, A.; Harsono, D.; Tafalla, M.; Fuente, A.; Visser, R.; Jørgensen, J. K.; Hogerheijde, M. R.

    2013-08-01

    Context. In the deeply embedded stage of star formation, protostars start to heat and disperse their surrounding cloud cores. The evolution of these sources has traditionally been traced through dust continuum spectral energy distributions (SEDs), but the use of CO excitation as an evolutionary probe has not yet been explored due to the lack of high-J CO observations. Aims: The aim is to constrain the physical characteristics (excitation, kinematics, column density) of the warm gas in low-mass protostellar envelopes using spectrally resolved Herschel data of CO and compare those with the colder gas traced by lower excitation lines. Methods: Herschel-HIFI observations of high-J lines of 12CO, 13CO, and C18O (up to Ju = 10, Eu up to 300 K) are presented toward 26 deeply embedded low-mass Class 0 and Class I young stellar objects, obtained as part of the Water In Star-forming regions with Herschel (WISH) key program. This is the first large spectrally resolved high-J CO survey conducted for these types of sources. Complementary lower J CO maps were observed using ground-based telescopes, such as the JCMT and APEX and convolved to matching beam sizes. Results: The 12CO 10-9 line is detected for all objects and can generally be decomposed into a narrow and a broad component owing to the quiescent envelope and entrained outflow material, respectively. The 12CO excitation temperature increases with velocity from ~60 K up to ~130 K. The median excitation temperatures for 12CO, 13CO, and C18O derived from single-temperature fits to the Ju = 2-10 integrated intensities are ~70 K, 48 K and 37 K, respectively, with no significant difference between Class 0 and Class I sources and no trend with Menv or Lbol. Thus, in contrast to the continuum SEDs, the spectral line energy distributions (SLEDs) do not show any evolution during the embedded stage. In contrast, the integrated line intensities of all CO isotopologs show a clear decrease with evolutionary stage as the envelope is

  5. A RECENT ACCRETION BURST IN THE LOW-MASS PROTOSTAR IRAS 15398-3359: ALMA IMAGING OF ITS RELATED CHEMISTRY

    SciTech Connect

    Jørgensen, Jes K.; Brinch, Christian; Lindberg, Johan E.; Bisschop, Suzanne E.; Visser, Ruud; Bergin, Edwin A.; Sakai, Nami; Yamamoto, Satoshi; Harsono, Daniel; Van Dishoeck, Ewine F.; Persson, Magnus V.

    2013-12-20

    Low-mass protostars have been suggested to show highly variable accretion rates throughout their evolution. Such changes in accretion, and related heating of their ambient envelopes, may trigger significant chemical variations on different spatial scales and from source-to-source. We present images of emission from C{sup 17}O, H{sup 13}CO{sup +}, CH{sub 3}OH, C{sup 34}S and C{sub 2}H toward the low-mass protostar IRAS 15398-3359 on 0.''5 (75 AU diameter) scales with the Atacama Large Millimeter/submillimeter Array at 340 GHz. The resolved images show that the emission from H{sup 13}CO{sup +} is only present in a ring-like structure with a radius of about 1-1.''5 (150-200 AU) whereas the CO and other high dipole moment molecules are centrally condensed toward the location of the central protostar. We propose that HCO{sup +} is destroyed by water vapor present on small scales. The origin of this water vapor is likely an accretion burst during the last 100-1000 yr increasing the luminosity of IRAS 15398-3359 by a factor of 100 above its current luminosity. Such a burst in luminosity can also explain the centrally condensed CH{sub 3}OH and extended warm carbon-chain chemistry observed in this source and furthermore be reflected in the relative faintness of its compact continuum emission compared to other protostars.

  6. Observational evidence for dissociative shocks in the inner 100 AU of low-mass protostars using Herschel-HIFI

    NASA Astrophysics Data System (ADS)

    Kristensen, L. E.; van Dishoeck, E. F.; Benz, A. O.; Bruderer, S.; Visser, R.; Wampfler, S. F.

    2013-09-01

    Aims: Herschel-HIFI spectra of H2O towards low-mass protostars show a distinct velocity component not seen in observations from the ground of CO or other species. The aim is to characterise this component in terms of excitation conditions and physical origin. Methods: A velocity component with an offset of ~10 km s-1 detected in spectra of the H2O 110-101 557 GHz transition towards six low-mass protostars in the "Water in star-forming regions with Herschel" (WISH) programme is also seen in higher-excited H2O lines. The emission from this component is quantified and local excitation conditions are inferred using 1D slab models. Data are compared to observations of hydrides (high-J CO, OH+, CH+, C+, OH) where the same component is uniquely detected. Results: The velocity component is detected in all six targeted H2O transitions (Eup ~ 50-250 K), as well as in CO 16-15 towards one source, Ser SMM1. Inferred excitation conditions imply that the emission arises in dense (n ~ 5 × 106-108 cm-3) and hot (T ~ 750 K) gas. The H2O and CO column densities are ≳1016 and 1018 cm-2, respectively, implying a low H2O abundance of ~10-2 with respect to CO. The high column densities of ions such as OH+ and CH+ (both ≳1013 cm-2) indicate an origin close to the protostar where the UV field is strong enough that these species are abundant. The estimated radius of the emitting region is 100 AU. This component likely arises in dissociative shocks close to the protostar, an interpretation corroborated by a comparison with models of such shocks. Furthermore, one of the sources, IRAS 4A, shows temporal variability in the offset component over a period of two years which is expected from shocks in dense media. High-J CO gas detected with Herschel-PACS with Trot ~ 700 K is identified as arising in the same component and traces the part of the shock where H2 reforms. Thus, H2O reveals new dynamical components, even on small spatial scales in low-mass protostars. Herschel is an ESA space

  7. The complex environment around the low-mass protostar IRAS 16293-2422

    NASA Astrophysics Data System (ADS)

    Schöier, Frederik L.; Jörgensen, Jes K.; Lahuis, Fred; van Dishoeck, Ewine F.; Blake, Geoff A.; Evans, Neal J.; C2d Irs Team

    The deeply embedded, low-mass, proto-binary star IRAS 16293-2422 has attained considerable interest over the last decade, in particular, driven by the detection of millimetre line emission from a large number of complex organic molecules and the possibility of this source harbouring a 'hot core', similar to those found in regions of high-mass star formation (e.g. van Dishoeck et al. 1995; Ceccarelli et al. 2000; Schöier et al. 2002; Cazaux et al. 2003). High angular resolution observations of the central core region of IRAS 16293-2422 have been carried out for a number of molecules using the BIMA and OVRO millimetre arrays (Schöier et al. 2005; see Figure 1 for examples). Most molecules show a separation of red (4-7 km s-1) and blue (0-4 km s-1) emission peaks roughly perpendicular to the large-scale outflow, thought to be driven by one of the protostars (MM1), indicative of rotation in the envelope. Some species, e.g. HNC and N2H+, also seem to trace the interaction of the outflow with the circumstellar material. The observed chemical differentiation of C18O, HNC, and N2H+ is consistent with the recent chemical model of IRAS 16293-2422 by Doty et al. (2004). Moreover, SiO and CH3OH appear to be partly associated with outflow activity where the ices are liberated by grain-grain collisions. We also report the detection of mid-infrared (23-35 μm) emission from IRAS 16293-2422 by the Spitzer Space Telescope infrared spectrograph, IRS (Jørgensen et al. 2005). The detection of mid-infrared emission suggests that the envelope is optically thin at these wavelengths. A detailed, spherically symmetric, radiative transfer model reproducing the full SED from 23 μm to 1.3mm requires a large, approximately 1000AU, inner cavity of the envelope in order to avoid quenching the emission from the central source (Figure 2). This corroborates a previous suggestion based on high angular resolution millimetre interferometric data (Schöier et al. 2004). An alternative

  8. The Spectral Signature of Accretion in Low-Mass Protostars: Observations and Non-LTE Modelling

    NASA Astrophysics Data System (ADS)

    Wiesemeyer, Helmut

    1997-06-01

    This work demonstrates the feasibility of a study bringing together theoretical concepts of the earliest phase of low-mass star formation and its observational evidence. Thus, two aspects have been considered: Observational evidence: In order to detect protostellar collapse by virtue of kinematical features in spectral line profiles, both optically thick and optically thin tracers are needed. According to Leung & Brown (1977, ApJ 214, L73), a protostellar envelope undergoing collapse exhibits a red-shifted self-absorption in a molecular line transition if the excitation gradient is negative. Optically thin emission (e.g. from the corresponding isotopomere's line) corroborates the conclusions by ruling out the case of independent components filling the observing beam. The nearby (d~200 pc) globular filament L 1082 (no. 9 from a catalog assembled by Schneider & Elmegreen, 1979, ApJS 41, 87) provides at least three candidates showing unambigeous footprints of protostellar collapse. By means of millimeter-interferometry (with the iram and bima interferometers Asz well as single dish spectroscopy and continuum imaging (using the iram 30 m telescope), these candidates were identified and characterized. As moderately optically thick high-density tracers, the CS (2,1), (3,2) and (5,4) transitions have been observed. The optically thin (2,1) lines of C34S and C18O were measured to confirm the evidence for collapse. Preliminary results from observations with isophot and isocam were used to better constrain the luminosity of one of the collapse candidates, which subsequently has been classified as an extreme Class 0 protostar. Theoretical concepts: For reasons evidenced by the observed column density distributions and by systematic shifts of the molecular line emission across the sources, spherically-symmetric collapse has to be ruled out. Instead, scenarios such as core formation in sheet-like clouds (as proposed by Hartmann et al., 1994, ApJ 430, L49) and magnetic accretion

  9. On the origin of H2CO abundance enhancements in low-mass protostars

    NASA Astrophysics Data System (ADS)

    Schöier, F. L.; Jørgensen, J. K.; van Dishoeck, E. F.; Blake, G. A.

    2004-04-01

    High angular resolution H2CO 218 GHz line observations have been carried out toward the low-mass protostars IRAS 16293-2422 and L1448-C using the Owens Valley Millimeter Array at ˜2 arcsec resolution. Simultaneous 1.37 mm continuum data reveal extended emission which is compared with that predicted by model envelopes constrained from single-dish data. For L1448-C the model density structure works well down to the 400 AU scale to which the interferometer is sensitive. For IRAS 16293-2422, a known proto-binary object, the interferometer observations indicate that the binary has cleared much of the material in the inner part of the envelope, out to the binary separation of ˜800 AU. For both sources there is excess unresolved compact emission centered on the sources, most likely due to accretion disks ⪉200 AU in size with masses of ⪆0.02 M⊙ (L1448-C) and ⪆0.1 M⊙ (IRAS 16293-2422). The H2CO data for both sources are dominated by emission from gas close to the positions of the continuum peaks. The morphology and velocity structure of the H2CO array data have been used to investigate whether the abundance enhancements inferred from single-dish modelling are due to thermal evaporation of ices or due to liberation of the ice mantles by shocks in the inner envelope. For IRAS 16293-2422 the H2CO interferometer observations indicate the presence of rotation roughly perpendicular to the large scale CO outflow. The H2CO distribution differs from that of C18O, with C18O emission peaking near MM1 and H2CO stronger near MM2. For L1448-C, the region of enhanced H2CO emission extends over a much larger scale >1'' than the radius of 50-100 K (0.6 arcsrec - 0.15 arcsec) where thermal evaporation can occur. The red-blue asymmetry of the emission is consistent with the outflow; however the velocities are significantly lower. The H2CO 322-221/303-202 flux ratio derived from the interferometer data is significantly higher than that found from single-dish observations for both

  10. Low-Mass Star Formation: From Molecular Cloud Cores to Protostars and Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Inutsuka, S.-I.; Machida, M.; Matsumoto, T.; Tsukamoto, Y.; Iwasaki, K.

    2016-05-01

    This review describes realistic evolution of magnetic field and rotation of the protostars, dynamics of outflows and jets, and the formation and evolution of protoplanetary disks. Recent advances in the protostellar collapse simulations cover a huge dynamic range from molecular cloud core density to stellar density in a self-consistent manner and account for all the non-ideal magnetohydrodynamical effects, such as Ohmic resistivity, ambipolar diffusion, and Hall current. We explain the emergence of the first core, i.e., the quasi-hydrostatic object that consists of molecular gas, and the second core, i.e., the protostar. Ohmic dissipation largely removes the magnetic flux from the center of a collapsing cloud core. A fast well-collimated bipolar jet along the rotation axis of the protostar is driven after the magnetic field is re-coupled with warm gas (˜103 K) around the protostar. The circumstellar disk is born in the "dead zone", a region that is de-coupled from the magnetic field, and the outer radius of the disk increases with that of the dead zone during the early accretion phase. The rapid increase of the disk size occurs after the depletion of the envelope of molecular cloud core. The effect of Hall current may create two distinct populations of protoplanetary disks.

  11. Reconnection X-winds: spin-down of low-mass protostars

    NASA Astrophysics Data System (ADS)

    Ferreira, Jonathan; Pelletier, Guy; Appl, Stefan

    2000-02-01

    We investigate the interaction of a protostellar magnetosphere with a large-scale magnetic field threading the surrounding accretion disc. It is assumed that a stellar dynamo generates a dipolar-type field with its magnetic moment aligned with the disc magnetic field. This leads to a magnetic neutral line at the disc mid-plane and gives rise to magnetic reconnection, converting closed protostellar magnetic flux into open field lines. These are simultaneously loaded with disc material, which is then ejected in a powerful wind. This process efficiently brakes down the protostar to 10-20per cent of the break-up velocity during the embedded phase.

  12. TENTATIVE DETECTION OF DEUTERATED METHANE TOWARD THE LOW-MASS PROTOSTAR IRAS 04368+2557 IN L1527

    SciTech Connect

    Sakai, Nami; Watanabe, Yoshimasa; Yamamoto, Satoshi; Shirley, Yancy L.; Sakai, Takeshi; Hirota, Tomoya

    2012-10-10

    The millimeter-wave rotational transition line (J{sub K} = 1{sub 0}-0{sub 0}) of deuterated methane CH{sub 3}D has tentatively been detected toward the low-mass Class 0 protostar IRAS 04368+2557 in L1527 with the Heinrich Hertz Submillimeter Telescope. This is the first detection of CH{sub 3}D in interstellar clouds, if confirmed. The column density and fractional abundance of CH{sub 3}D are determined to be (9.1 {+-} 3.4) Multiplication-Sign 10{sup 15} cm{sup -2} and (3.0 {+-} 1.1) Multiplication-Sign 10{sup -7}, respectively, where we assume the rotational temperature of 25 K. The column density and fractional abundance of the gaseous CH{sub 4} are estimated to be (1.3-4.6) Multiplication-Sign 10{sup 17} cm{sup -2} and (4.3-15.2) Multiplication-Sign 10{sup -6}, respectively, by adopting the molecular D/H ratios of 2%-7% reported for various molecules in L1527. The fractional abundance of CH{sub 4} is higher than or comparable to that found in high-mass star-forming cores by infrared observations. It is sufficiently high to trigger the efficient production of various carbon-chain molecules in a lukewarm region near the protostar, which supports the scenario of warm carbon-chain chemistry.

  13. Constraining the physical structure of the inner few 100 AU scales of deeply embedded low-mass protostars

    NASA Astrophysics Data System (ADS)

    Persson, M. V.; Harsono, D.; Tobin, J. J.; van Dishoeck, E. F.; Jørgensen, J. K.; Murillo, N.; Lai, S.-P.

    2016-05-01

    Context. The physical structure of deeply embedded low-mass protostars (Class 0) on scales of less than 300 AU is still poorly constrained. While molecular line observations demonstrate the presence of disks with Keplerian rotation toward a handful of sources, others show no hint of rotation. Determining the structure on small scales (a few 100 AU) is crucial for understanding the physical and chemical evolution from cores to disks. Aims: We determine the presence and characteristics of compact, disk-like structures in deeply embedded low-mass protostars. A related goal is investigating how the derived structure affects the determination of gas-phase molecular abundances on hot-core scales. Methods: Two models of the emission, a Gaussian disk intensity distribution and a parametrized power-law disk model, are fitted to subarcsecond resolution interferometric continuum observations of five Class 0 sources, including one source with a confirmed Keplerian disk. Prior to fitting the models to the de-projected real visibilities, the estimated envelope from an independent model and any companion sources are subtracted. For reference, a spherically symmetric single power-law envelope is fitted to the larger scale emission (~1000 AU) and investigated further for one of the sources on smaller scales. Results: The radii of the fitted disk-like structures range from ~90-170 AU, and the derived masses depend on the method. Using the Gaussian disk model results in masses of 54-556 × 10-3 M⊙, and using the power-law disk model gives 9-140 × 10-3 M⊙. While the disk radii agree with previous estimates the masses are different for some of the sources studied. Assuming a typical temperature distribution (r-0.5), the fractional amount of mass in the disk above 100 K varies from 7% to 30%. Conclusions: A thin disk model can approximate the emission and physical structure in the inner few 100 AU scales of the studied deeply embedded low-mass protostars and paves the way for

  14. H_2CO and CH_3OH abundances in the envelopes around low-mass protostars

    NASA Astrophysics Data System (ADS)

    Jørgensen, J. K.; Schöier, F. L.; van Dishoeck, E. F.

    2005-07-01

    This paper presents the third in a series of single-dish studies of molecular abundances in the envelopes around a large sample of 18 low-mass pre- and protostellar objects. It focuses on typical grain mantle products and organic molecules, including H2CO, CH3OH and CH3CN. With a few exceptions, all H2CO lines can be fit by constant abundances of 7× 10-11{-}8× 10-9 throughout the envelopes if ortho- and para lines are considered independently. The current observational dataset does not require a large H2CO abundance enhancement in the inner warm regions, but this can also not be ruled out. Through comparison of the H2CO abundances of the entire sample, the H2CO ortho-para ratio is constrained to be 1.6 ± 0.3 consistent with thermalization on grains at temperatures of 10-15 K. The H2CO abundances can be related to the empirical chemical network established on the basis of our previously reported survey of other species and is found to be closely correlated with that of the nitrogen-bearing molecules. These correlations reflect the freeze-out of molecules at low temperatures and high densities, with the constant H2CO abundance being a measure of the size of the freeze-out zone. An improved fit to the data is obtained with a "drop" abundance structure in which the abundance is typically a few ×10-10 when the temperature is lower than the evaporation temperature and the density high enough so that the timescale for depletion is less than the lifetime of the core. The location of the freeze-out zone is constrained from CO observations. Outside the freeze-out zone, the H2CO abundance is typically a few × 10-9{-}10-8. The observations show that the CH3OH lines are significantly broader than the H2CO lines, indicating that they probe kinematically distinct regions. CH3OH is moreover only detected toward a handful of sources and CH3CN toward only one, NGC 1333-IRAS2. For NGC 1333-IRAS2, CH3OH and CH3CN abundance enhancements of two-three orders of magnitude at

  15. The low-mass YSO CB230-A: investigating the protostar and its jet with NIR spectroscopy and Spitzer observations

    NASA Astrophysics Data System (ADS)

    Massi, F.; Codella, C.; Brand, J.; di Fabrizio, L.; Wouterloot, J. G. A.

    2008-11-01

    scenario is that CB230-A is a Class 0/I YSO driving an atomic jet that is observed to be almost monopolar probably due to its inclination to the plane of the sky and the resulting higher extinction of its red side. This primary jet appears to be sufficiently energetic to open the cavity visible in the NIR images and drive the large-scale molecular outflow observed at mm-wavelengths. CB230-A was revealed to be a good location to test the innermost structure of accreting low-mass protostars. Appendices A and B are only available in electronic form at http://www.aanda.org

  16. HIGH D{sub 2}O/HDO RATIO IN THE INNER REGIONS OF THE LOW-MASS PROTOSTAR NGC 1333 IRAS2A

    SciTech Connect

    Coutens, A.; Jørgensen, J. K.; Persson, M. V.; Van Dishoeck, E. F.; Vastel, C.; Taquet, V.

    2014-09-01

    Water plays a crucial role both in the interstellar medium and on Earth. To constrain its formation mechanisms and its evolution through the star formation process, the determination of the water deuterium fractionation ratios is particularly suitable. Previous studies derived HDO/H{sub 2}O ratios in the warm inner regions of low-mass protostars. We here report a detection of the D{sub 2}O 1{sub 1,} {sub 0}-1{sub 0,} {sub 1} transition toward the low-mass protostar NGC 1333 IRAS2A with the Plateau de Bure interferometer: this represents the first interferometric detection of D{sub 2}O—and only the second solar-type protostar for which this isotopologue is detected. Using the observations of the HDO 5{sub 4,} {sub 2}-6{sub 3,} {sub 3} transition simultaneously detected and three other HDO lines previously observed, we show that the HDO line fluxes are well reproduced with a single excitation temperature of 218 ± 21 K and a source size of ∼0.''5. The D{sub 2}O/HDO ratio is ∼(1.2 ± 0.5) × 10{sup –2}, while the use of previous H{sub 2}{sup 18}O observations give an HDO/H{sub 2}O ratio of ∼(1.7 ± 0.8) × 10{sup –3}, i.e., a factor of seven lower than the D{sub 2}O/HDO ratio. These results contradict the predictions of current grain surface chemical models and indicate that either the surface deuteration processes are poorly understood or that both sublimation of grain mantles and water formation at high temperatures (≳230 K) take place in the inner regions of this source. In the second scenario, the thermal desorption of the grain mantles would explain the high D{sub 2}O/HDO ratio, while water formation at high temperature would explain significant extra production of H{sub 2}O leading to a decrease of the HDO/H{sub 2}O ratio.

  17. MAGNETIC FIELD STRUCTURE AROUND LOW-MASS CLASS 0 PROTOSTARS: B335, L1527, AND IC348-SMM2

    SciTech Connect

    Davidson, J. A.; Novak, G.; Matthews, T. G.; Matthews, B.; Goldsmith, P. F.; Chapman, N.; Volgenau, N. H.; Vaillancourt, J. E.; Attard, M.

    2011-05-10

    We report new 350 {mu}m polarization observations of the thermal dust emission from the cores surrounding the low-mass, Class 0 young stellar objects L1527, IC348-SMM2, and B335. We have inferred magnetic field directions from these observations and have used them together with results in the literature to determine whether magnetically regulated core-collapse and star formation models are consistent with the observations. These models predict a pseudo-disk with its symmetry axis aligned with the core magnetic field. The models also predict a magnetic field pinch structure on a scale less than or comparable to the infall radii for these sources. In addition, if the core magnetic field aligns (or nearly aligns) the core rotation axis with the magnetic field before core collapse, then the models predict the alignment (or near alignment) of the overall pinch field structure with the bipolar outflows in these sources. We show that if one includes the distorting effects of bipolar outflows on magnetic fields, then in general the observational results for L1527 and IC348-SMM2 are consistent with these magnetically regulated models. We can say the same for B335 only if we assume that the distorting effects of the bipolar outflow on the magnetic fields within the B335 core are much greater than for L1527 and IC348-SMM2. We show that the energy densities of the outflows in all three sources are large enough to distort the magnetic fields predicted by magnetically regulated models.

  18. B-1B excels in conventional role

    SciTech Connect

    Scott, W.B.

    1992-07-01

    A report is presented of an observational flight performed in a USAF B-1B to better understand the operational aspects of the aircraft's new conventional bombing mission as an integral element of a multiaircraft tactical strike package. The basic flight plan consisted of a standard takeoff and climb, cruising to the training area at 22,000 ft, descending for a 400 ft low-level run, making two simulated bomb drops, and climbing back to 25,000 ft for the return to base. Attention is given the new/enhanced avionics, the ALQ-161 defensive electronic warfare system and ripple-release Mk. 82 bombing procedures.

  19. Computational Modeling of the Class I Low-Mass Protostar Elias 29 Applying Optical Constants of Ices Processed By High Energy Cosmic Ray Analogs

    NASA Astrophysics Data System (ADS)

    Rocha, W. R. M.; Pilling, S.

    2015-04-01

    We present a study of the effects of high energy cosmic rays (CRs) over the astrophysical ices, observed toward the embedded class I protostar Elias 29, by using computational modeling and laboratory data. Its spectrum was observed with the Infrared Space Observatory (ISO) covering 2.3-190 μm. The modeling employed the three-dimensional Monte Carlo radiative transfer code RADMC-3D and laboratory data of bombarded ice grains by CR analogs and unprocessed ices (not bombarded). We are assuming that Elias 29 has a self-irradiated disk with inclination i = 60.°0, surrounded by an envelope with a bipolar cavity. The results show that absorption features toward Elias 29 are better reproduced by assuming a combination between unprocessed astrophysical ices at low temperature (H2O, CO, CO2) and bombarded ices (H2O:CO2) by high energy CRs. Evidences of the ice processing around Elias 29 can be observed by the good fitting around 5.5-8.0 μm, by polar and apolar ice segregation in 15.15-15.25 μm, and by the presence of the CH4 and HCOOH ices. Given that non-nitrogen compounds were employed in this work, we assume that absorption around 5.5-8.0 μm should not be associated with the NH4+ ion (see the 2003 work of Shutte & Khanna ), but more probably with aliphatic ethers (e.g., R1-OCH2-R2), CH3CHO, and related species. The results obtained in this paper are important because they show that the environment around protostars is better modeled considering processed samples and, consequently, demonstrate the chemical evolution of the astrophysical ices.

  20. Phylogeography of E1b1b1b-M81 haplogroup and analysis of its subclades in Morocco.

    PubMed

    Reguig, Ahmed; Harich, Nourdin; Barakat, Abdelhamid; Rouba, Hassan

    2014-01-01

    In this study we analyzed 295 unrelated Berber-speaking men from northern, central, and southern Morocco to characterize frequency of the E1b1b1b-M81 haplogroup and to refine the phylogeny of its subclades: E1b1b1b1-M107, E1b1b1b2-M183, and E1b1b1b2a-M165. For this purpose, we typed four biallelic polymorphisms: M81, M107, M183, and M165. A large majority of the Berber-speaking male lineages belonged to the Y-chromosomal E1b1b1b-M81 haplogroup. The frequency ranged from 79.1% to 98.5% in all localities sampled. E1b1b1b2-M183 was the most dominant subclade in our samples, ranging from 65.1% to 83.1%. In contrast, the E1b1b1b1-M107 and E1b1b1b2a-M165 subclades were not found in our samples. Our results suggest a predominance of the E1b1b1b-M81 haplogroup among Moroccan Berber-speaking males with a decreasing gradient from south to north. The most prevalent subclade in this haplogroup was E1b1b1b2-M183, for which diffferences among these three groups were statistically significant between central and southern groups. PMID:25397701

  1. The jet and the disk of the HH 212 low-mass protostar imaged by ALMA: SO and SO2 emission

    NASA Astrophysics Data System (ADS)

    Podio, L.; Codella, C.; Gueth, F.; Cabrit, S.; Bachiller, R.; Gusdorf, A.; Lee, C.-F.; Lefloch, B.; Leurini, S.; Nisini, B.; Tafalla, M.

    2015-09-01

    Context. The investigation of the disk formation and jet launching mechanism in protostars is crucial to understanding the earliest stages of star and planet formation. Aims: We aim to constrain the physical and dynamical properties of the molecular jet and disk of the HH 212 protostellar system at unprecedented angular scales, exploiting the capabilities of the Atacama Large Millimeter Array (ALMA). Methods: The ALMA observations of HH 212 in emission lines from sulfur-bearing molecules, SO 98-87, SO 1011-1010, SO282,6-71,7, are compared with simultaneous CO 3-2, SiO 8-7 data. The molecules column density and abundance are estimated using simple radiative transfer models. Results: SO 98-87 and SO282,6-71,7 show broad velocity profiles. At systemic velocity, they probe the circumstellar gas and the cavity walls. Going from low to high blue- and red-shifted velocities the emission traces the wide-angle outflow and the fast (~100-200 km s-1), collimated (~90 AU) molecular jet revealing the inner knots with timescales ≤50 yr. The jet transports a mass-loss rate ≥ 0.2-2 × 10-6 M⊙ yr-1, implying high ejection efficiency (≥ 0.03-0.3). The SO and SO2 abundances in the jet are ~ 10-7-10-6. SO 1011-1010 emission is compact and shows small-scale velocity gradients, indicating that it originates partly from the rotating disk previously seen in HCO+ and C17O, and partly from the base of the jet. The disk mass is ≥ 0.002-0.013 M⊙ and the SO abundance in the disk is ~ 10-8-10-7. Conclusions: SO and SO2 are effective tracers of the molecular jet in the inner few hundreds AU from the protostar. Their abundances indicate that 1-40% of sulfur is in SO and SO2 due to shocks in the jet/outflow and/or to ambipolar diffusion at the wind base. The SO abundance in the disk is 3-4 orders of magnitude larger than in evolved protoplanetary disks. This may be due to an SO enhancement in the accretion shock at the envelope-disk interface or in spiral shocks if the disk is partly

  2. Herschel Key Program, "Dust, Ice, and Gas In Time" (DIGIT): The Origin of Molecular and Atomic Emission in Low-mass Protostars in Taurus

    NASA Astrophysics Data System (ADS)

    Lee, Jeong-Eun; Lee, Jinhee; Lee, Seokho; Evans, Neal J., II; Green, Joel D.

    2014-10-01

    Six low-mass embedded sources (L1489, L1551-IRS5, TMR1, TMC1-A, L1527, and TMC1) in Taurus have been observed with Herschel-PACS to cover the full spectrum from 50 to 210 μm as part of the Herschel key program, "Dust, Ice, and Gas In Time." The relatively low intensity of the interstellar radiation field surrounding Taurus minimizes contamination of the [C II] emission associated with the sources by diffuse emission from the cloud surface, allowing study of the [C II] emission from the source. In several sources, the [C II] emission is distributed along the outflow, as is the [O I] emission. The atomic line luminosities correlate well with each other, as do the molecular lines, but the atomic and molecular lines correlate poorly. The relative contribution of CO to the total gas cooling is constant at ~30%, while the cooling fraction by H2O varies from source to source, suggesting different shock properties resulting in different photodissociation levels of H2O. The gas with a power-law temperature distribution with a moderately high density can reproduce the observed CO fluxes, indicative of CO close to LTE. However, H2O is mostly subthermally excited. L1551-IRS5 is the most luminous source (Łbol = 24.5 L ⊙) and the [O I] 63.1 μm line accounts for more than 70% of its FIR line luminosity, suggesting complete photodissociation of H2O by a J shock. In L1551-IRS5, the central velocity shifts of the [O I] line, which exceed the wavelength calibration uncertainty (~70 km s-1) of PACS, are consistent with the known redshifted and blueshifted outflow direction.

  3. Distributed low-mass star formation in the IRDC G34.43+00.24

    SciTech Connect

    Foster, Jonathan B.; Arce, Héctor G.; Offner, Stella; Kassis, Marc; Sanhueza, Patricio; Jackson, James M.; Finn, Susanna C.; Sakai, Takeshi; Sakai, Nami; Yamamoto, Satoshi; Guzmán, Andrés E.; Rathborne, Jill M.

    2014-08-20

    We have used deep near-infrared observations with adaptive optics to discover a distributed population of low-mass protostars within the filamentary Infrared Dark Cloud G34.43+00.24. We use maps of dust emission at multiple wavelengths to determine the column density structure of the cloud. In combination with an empirically verified model of the magnitude distribution of background stars, this column density map allows us to reliably determine overdensities of red sources that are due to embedded protostars in the cloud. We also identify protostars through their extended emission in the K band, which comes from excited H{sub 2} in protostellar outflows or reflection nebulosity. We find a population of distributed low-mass protostars, suggesting that low-mass protostars may form earlier than, or contemporaneously with, high-mass protostars in such a filament. The low-mass protostellar population may also produce the narrow line-width SiO emission observed in some clouds without high-mass protostars. Finally, we use a molecular line map of the cloud to determine the virial parameter per unit length along the filament and find that the highest mass protostars form in the most bound portion of the filament, as suggested by theoretical models.

  4. High fat diet deviates PtC-specific B1 B cell phagocytosis in obese mice

    PubMed Central

    Vo, Hung; Chiu, Joanna; Allaimo, Danielle; Mao, Changchuin; Wang, Yaqi; Gong, Yuefei; Ow, Hooisweng; Porter, Tyrone; Zhong, Xuemei

    2014-01-01

    Phagocytosis had been attributed predominantly to “professional” phagocytes such as macrophages, which play critical roles in adipose tissue inflammation. However, recently, macrophage-like phagocytic activity has been reported in B1 B lymphocytes. Intrigued by the long-established correlation between high fat diet (HFD)-induced obesity and immune dysfunction, we investigated how HFD affects B1 B cell phagocytosis. A significant number of B1 B cells recognize phosphatidylcholine (PtC), a common phospholipid component of cell membrane. We report here that unlike macrophages, B1 B cells have a unique PtC-specific phagocytic function. In the presence of both PtC-coated and non-PtC control fluorescent nano-particles, B1 B cells from healthy lean mice selectively engulfed PtC-coated beads, whereas B1 B cells from HFD-fed obese mice non-discriminately phagocytosed both PtC-coated and control beads. Morphologically, B1 B cells from obese mice resembled macrophages, displaying enlarged cytosol and engulfed more beads. Our study suggests for the first time that HFD can affect B1 B cell phagocytosis, substantiating the link of HFD-induced obesity and immune deviation. PMID:25866632

  5. Hydroxysteroid sulfotransferase 2B1b expression and localization in normal human brain

    PubMed Central

    Salman, Emily D.; Faye-Petersen, Ona; Falany, Charles N.

    2012-01-01

    Steroid sulfonation in the human brain has not been well characterized. The major sulfotransferase (SULT) isoforms that conjugate steroids in humans are SULT1E1, SULT2A1, and SULT2B1b. SULT2B1b catalyzes the sulfonation of 3β-hydroxysteroids, including neurosteroids dehydroepiandrosterone and pregnenolone, as well as cholesterol and several hydroxycholesterols. SULT2B1b mRNA and protein expression were detected in adult and fetal human brain sections, whereas neither mRNA, nor protein expression were identified for SULT1E1 or SULT2A1. Using immunohistochemical analysis, SULT2B1b expression was detected in neurons and oligodendrocytes in adult brain and in epithelial tissues in 28-week-old fetal brain. Sulfonation of cholesterol, oxysterols, and neurosteroids in the brain is apparently catalyzed by SULT2B1b since expression of neither SULT2A1 nor SULT1E1 was detected in human brain sections. SULT2B1b mRNA and protein were also detected in human U373-MG glioblastoma cells. Both mRNA and protein expression of liver X receptor (LXR)-β, but not LXR-α, were detected in U373-MG cells, and LXR-β activation resulted in a decrease in SULT2B1b protein expression. Since hydroxycholesterols are important physiological LXR activators, this suggests a role for regulation of sterol metabolism by LXR and SULT2B1b. Therefore, elucidating key enzymes in the metabolism of cholesterol and neurosteroids could help define the properties of steroid conjugation in the human brain. PMID:24683427

  6. B1b cells recognize protective antigens after natural infection and vaccination.

    PubMed

    Cunningham, Adam F; Flores-Langarica, Adriana; Bobat, Saeeda; Dominguez Medina, Carmen C; Cook, Charlotte N L; Ross, Ewan A; Lopez-Macias, Constantino; Henderson, Ian R

    2014-01-01

    There are multiple, distinct B-cell populations in human beings and other animals such as mice. In the latter species, there is a well-characterized subset of B-cells known as B1 cells, which are enriched in peripheral sites such as the peritoneal cavity but are rare in the blood. B1 cells can be further subdivided into B1a and B1b subsets. There may be additional B1 subsets, though it is unclear if these are distinct populations or stages in the developmental process to become mature B1a and B1b cells. A limitation in understanding B1 subsets is the relative paucity of specific surface markers. In contrast to mice, the existence of B1 cells in human beings is controversial and more studies are needed to investigate the nature of these enigmatic cells. Examples of B1b antigens include pneumococcal polysaccharide and the Vi antigen from Salmonella Typhi, both used routinely as vaccines in human beings and experimental antigens such as haptenated-Ficoll. In addition to inducing classical T-dependent responses some proteins are B1b antigens and can induce T-independent (TI) immunity, examples include factor H binding protein from Borrelia hermsii and porins from Salmonella. Therefore, B1b antigens can be proteinaceous or non-proteinaceous, induce TI responses, memory, and immunity, they exist in a diverse range of pathogenic bacteria, and a single species can contain multiple B1b antigens. An unexpected benefit to studying B1b cells is that they appear to have a propensity to recognize protective antigens in bacteria. This suggests that studying B1b cells may be rewarding for vaccine design as immunoprophylactic and immunotherapeutic interventions become more important due to the decreasing efficacy of small molecule antimicrobials. PMID:25400633

  7. B1b Cells Recognize Protective Antigens after Natural Infection and Vaccination

    PubMed Central

    Cunningham, Adam F.; Flores-Langarica, Adriana; Bobat, Saeeda; Dominguez Medina, Carmen C.; Cook, Charlotte N. L.; Ross, Ewan A.; Lopez-Macias, Constantino; Henderson, Ian R.

    2014-01-01

    There are multiple, distinct B-cell populations in human beings and other animals such as mice. In the latter species, there is a well-characterized subset of B-cells known as B1 cells, which are enriched in peripheral sites such as the peritoneal cavity but are rare in the blood. B1 cells can be further subdivided into B1a and B1b subsets. There may be additional B1 subsets, though it is unclear if these are distinct populations or stages in the developmental process to become mature B1a and B1b cells. A limitation in understanding B1 subsets is the relative paucity of specific surface markers. In contrast to mice, the existence of B1 cells in human beings is controversial and more studies are needed to investigate the nature of these enigmatic cells. Examples of B1b antigens include pneumococcal polysaccharide and the Vi antigen from Salmonella Typhi, both used routinely as vaccines in human beings and experimental antigens such as haptenated-Ficoll. In addition to inducing classical T-dependent responses some proteins are B1b antigens and can induce T-independent (TI) immunity, examples include factor H binding protein from Borrelia hermsii and porins from Salmonella. Therefore, B1b antigens can be proteinaceous or non-proteinaceous, induce TI responses, memory, and immunity, they exist in a diverse range of pathogenic bacteria, and a single species can contain multiple B1b antigens. An unexpected benefit to studying B1b cells is that they appear to have a propensity to recognize protective antigens in bacteria. This suggests that studying B1b cells may be rewarding for vaccine design as immunoprophylactic and immunotherapeutic interventions become more important due to the decreasing efficacy of small molecule antimicrobials. PMID:25400633

  8. Protostar mass functions in young clusters

    SciTech Connect

    Myers, Philip C.

    2014-01-20

    In an improved model of protostar mass functions (PMFs), protostars gain mass from isothermal cores in turbulent clumps. Their mass accretion rate is similar to Shu accretion at low mass and to reduced Bondi accretion at high mass. Accretion durations follow a simple expression in which higher-mass protostars accrete for longer times. These times are set by ejections, stellar feedback, and gravitational competition, which terminate accretion and reduce its efficiency. The mass scale is the mass of a critically stable isothermal core. In steady state, the PMF approaches a power law at high mass because of competition between clump accretion and accretion stopping. The power law exponent is the ratio of the timescales of accretion and accretion stopping. The protostar luminosity function (PLF) peaks near 1 L {sub ☉} because of inefficient accretion of core gas. Models fit observed PLFs in four large embedded clusters. These indicate that their underlying PMFs may be top-heavy compared with the initial mass function, depending on the protostar radius model.

  9. Three micron spectroscopy of low-mass pre-main-sequence stars

    SciTech Connect

    Sato, Shuji; Nagata, Tetsuya; Tanaka, Masuo; Yamamoto, Tetsuo Kyoto Univ. Tokyo Univ. Institute of Space and Astronautical Science, Sagamihara )

    1990-08-01

    Low-resolution spectra were obtained of 16 premain-sequence stars, and ice-band features are detected in young T Tauri stars (TTSs) and in low-mass protostars. The TTSs have an ice band optical depth tau(ice) of 0.1-0.4. The tau(ice) for objects in the Taurus dark cloud decreases progressively from protostars to TTSs. The apparent color temperatures of the continuum spectra are 800-1200 K for protostars and 1100-1500 K for TTSs. The color temperatures of the continuum increase to 1200-2000K after correcting the protostar spectra for foreground extinction. This common temperature range in both young TTSs and protostars suggests that the inner boundary of the circumstellar disk is determined by the sublimation of refractory grains. 39 refs.

  10. The capsular polysaccharide Vi from Salmonella Typhi is a B1b antigen

    PubMed Central

    Marshall, Jennifer L.; Flores-Langarica, Adriana; Kingsley, Robert A.; Hitchcock, Jessica R.; Ross, Ewan A.; Lopez-Macias, Constantino; Lakey, Jeremy; Martin, Laura B.; Toellner, Kai-Michael; MacLennan, Calman A.; MacLennan, Ian C; Henderson, Ian R.; Dougan, Gordon; Cunningham, Adam F.

    2012-01-01

    Vaccination with purified capsular polysaccharide Vi antigen from Salmonella Typhi can protect against typhoid fever, although the mechanism for its efficacy is not clearly established. Here, we have characterised the B cell response to this vaccine in wild-type and T cell-deficient mice. We show that immunization with Typhim Vi rapidly induces proliferation in B1b peritoneal cells, but not in B1a cells or marginal zone (MZ) B cells. This induction of B1b proliferation is concomitant with the detection of splenic Vi-specific antibody secreting cells and protective antibody and Rag1-deficient B1b cell chimeras generated by adoptive transfer induced specific antibody after Vi immunization. Furthermore, antibody derived from peritoneal B cells is sufficient to confer protection against Salmonella that express Vi antigen. Expression of Vi by Salmonella during infection did not inhibit the development of early antibody responses to non-Vi antigens. Despite this, the protection conferred by immunization of mice with porin proteins from Salmonella, which induce antibody-mediated protection, was reduced after infection with Vi-expressing Salmonella, although protection was not totally abrogated. This work therefore suggests that in mice, B1b cells contribute to the protection induced by Vi antigen and targeting non-Vi antigens as sub-unit vaccines may offer an attractive strategy to augment current Vi-based vaccine strategies. PMID:23162127

  11. Studies of low-mass star formation with the large deployable reflector

    NASA Technical Reports Server (NTRS)

    Hollenbach, D. J.; Tielens, Alexander G. G. M.

    1984-01-01

    Estimates are made of the far-infrared and submillimeter continuum and line emission from regions of low mass star formation. The intensity of this emission is compared with the sensitivity of the large deployable reflector (LDR), a large space telescope designed for this wavelength range. The proposed LDR is designed to probe the temperature, density, chemical structure, and the velocity field of the collapsing envelopes of these protostars. The LDR is also designed to study the accretion shocks on the cores and circumstellar disks of low-mass protostars, and to detect shock waves driven by protostellar winds.

  12. Intrinsic fluorescence spectra characteristics of vitamin B1, B2, and B6

    NASA Astrophysics Data System (ADS)

    Yang, Hui; Xiao, Xue; Zhao, Xuesong; Hu, Lan; Lv, Caofang; Yin, Zhangkun

    2015-11-01

    This paper presents the intrinsic fluorescence characteristics of vitamin B1, B2 and B6 measured with 3D fluorescence Spectrophotometer. Three strong fluorescence areas of vitamin B2 locate at λex/λem=270/525nm, 370/525nm and 450/525nm, one fluorescence areas of vitamin B1 locates at λex/λem=370/460nm, two fluorescence areas of vitamin B6 locates at λex/λem=250/370nm and 325/370nm were found. The influence of pH of solution to the fluorescence profile was also discussed. Using the PARAFAC algorithm, 10 vitamin B1, B2 and B6 mixed solutions were successfully decomposed, and the emission profiles, excitation profiles, central wavelengths and the concentration of the three components were retrieved precisely through about 5 iteration times.

  13. Plant compounds that induce polychlorinated biphenyl biodegradation by Arthrobacter sp. strain B1B.

    PubMed Central

    Gilbert, E S; Crowley, D E

    1997-01-01

    Plant compounds that induced Arthrobacter sp. strain B1B to cometabolize polychlorinated biphenyls (PCBs) were identified by a screening assay based on the formation of a 4,4'-dichlorobiphenyl ring fission product. A chemical component of spearmint (Mentha spicata), l-carvone, induced Arthrobacter sp. strain B1B to cometabolize Aroclor 1242, resulting in significant degradation of 26 peaks in the mixture, including selected tetra- and pentachlorobiphenyls. Evidence for PCB biodegradation included peak disappearance, formation of a phenylhexdienoate ring fission product, and chlorobenzoate accumulation in the culture supernatant. Carvone was not utilized as a growth substrate and was toxic at concentrations of greater than 500 mg liter-1. Several compounds structurally related to l-carvone, including limonene, p-cymene, and isoprene, also induced cometabolism of PCBs by Arthrobacter sp. strain B1B. A structure-activity analysis showed that chemicals with an unsaturated p-menthane structural motif promoted the strongest cometabolism activity. These data suggest that certain plant-derived terpenoids may be useful for promoting enhanced rates of PCB biodegradation by soil bacteria. PMID:9143124

  14. Hydroxysteroid Sulfotransferase SULT2B1b Promotes Hepatocellular Carcinoma Cells Proliferation In Vitro and In Vivo

    PubMed Central

    Yang, Xiaoming; Xu, Yali; Guo, Fenghua; Ning, Yanxia; Zhi, Xiuling; Yin, Lianhua; Li, Xiaobo

    2013-01-01

    Hydroxysteroid sulfotransferase 2B1b (SULT2B1b) is highly selective for the addition of sulfate groups to 3β-hydroxysteroids. Although previous reports have suggested that SULT2B1b is correlated with cell proliferation of hepatocytes, the relationship between SULT2B1b and the malignant phenotype of hepatocarcinoma cells was not clear. In the present study, we found that SULT2B1 was comparatively higher in the human hepatocarcinoma tumorous tissues than their adjacent tissues. Besides, SULT2B1b overexpression promoted the growth of the mouse hepatocarcinoma cell line Hepa1-6, while Lentivirus-mediated SULT2B1b interference inhibited growth as assessed by the CCK-8 assay. Likewise, inhibition of SULT2B1b expression induced cell-cycle arrest and apoptosis in Hepa1-6 cells by upregulating the expression of FAS, downregulating the expression of cyclinB1, BCL2 and MYC in vitro and in vivo at both the transcript and protein levels. Knock-down of SULT2B1b expression significantly suppressed tumor growth in nude mouse xenografts. Moreover, proliferation rates and SULT2B1b expression were highly correlated in the human hepatocarcinoma cell lines Huh-7, Hep3B, SMMC-7721 and BEL-7402 cells. Knock-down of SULT2B1b inhibited cell growth and cyclinB1 levels in human hepatocarcinoma cells and suppressed xenograft growth in vivo. In conclusion, SULT2B1b expression promotes proliferation of hepatocellular carcinoma cells in vitro and in vivo, which may contribute to the progression of HCC. PMID:23593328

  15. CLASS 0 PROTOSTARS IN THE PERSEUS MOLECULAR CLOUD: A CORRELATION BETWEEN THE YOUNGEST PROTOSTARS AND THE DENSE GAS DISTRIBUTION

    SciTech Connect

    Sadavoy, S. I.; Di Francesco, J.; André, Ph.; Maury, A.; Men'shchikov, A.; Motte, F.; Hennemann, M.; Könyves, V.; Louvet, F.; Roy, A.; Bernard, J.-P.; Nguyên-Lu'o'ng, Q.; Schneider, N.; Bontemps, S.; Arzoumanian, D.; Hill, T.; Peretto, N.; and others

    2014-06-01

    We use PACS and SPIRE continuum data at 160 μm, 250 μm, 350 μm, and 500 μm from the Herschel Gould Belt Survey to sample seven clumps in Perseus: B1, B1-E, B5, IC 348, L1448, L1455, and NGC 1333. Additionally, we identify and characterize the embedded Class 0 protostars using detections of compact Herschel sources at 70 μm as well as archival Spitzer catalogs and SCUBA 850 μm photometric data. We identify 28 candidate Class 0 protostars, four of which are newly discovered sources not identified with Spitzer. We find that the star formation efficiency of clumps, as traced by Class 0 protostars, correlates strongly with the flatness of their respective column density distributions at high values. This correlation suggests that the fraction of high column density material in a clump reflects only its youngest protostellar population rather than its entire source population. We propose that feedback from either the formation or evolution of protostars changes the local density structure of clumps.

  16. Episodic Accretion among the Orion Protostars

    NASA Astrophysics Data System (ADS)

    Fischer, William J.; Safron, Emily; Megeath, S. Thomas

    2016-06-01

    Episodic accretion, where a young stellar object undergoes stochastic spikes in its disk-to-star accretion rate one or more times over its formation period, may be a crucial process in the formation of low-mass stars. These spikes result in a factor of 10 to 100 increase in the source luminosity over the course of several months that may persist for years. Six years after the Spitzer survey of the Orion molecular clouds, the WISE telescope mapped Orion with similar wavelength coverage. Thus, the two surveys can be used to explore the mid-infrared variability of young stars on this timescale, which is suitable for discovering episodic accretion events. Out of 319 Orion protostars that were targets of the Herschel Orion Protostar Survey, we identified two examples of episodic accretion with this method. One of them, HOPS 223, was previously known. The other, HOPS 383, is the first known example of episodic accretion in a Class 0 protostar (age < 0.2 Myr). With these and one other outburst that began early in the Spitzer mission, we estimate that the most likely interval between protostellar outbursts is 740 years, with a 90% confidence interval of 470 to 6200 years. These outbursts are weaker than the optically revealed FU Ori events. We will update the mid-infrared light curves of HOPS 223 and HOPS 383 with recent data from FORCAST aboard SOFIA; HOPS 223 shows signs of fading.

  17. ABCG1 is required for pulmonary B-1 B cell and natural antibody homeostasis

    PubMed Central

    Baldan, Angel; Gonen, Ayelet; Choung, Christina; Que, Xuchu; Marquart, Tyler J.; Hernandez, Irene; Bjorkhem, Ingemar; Ford, David A.; Witztum, Joseph L.; Tarling, Elizabeth J.

    2014-01-01

    Many metabolic diseases, including atherosclerosis, type 2 diabetes, pulmonary alveolar proteinosis (PAP), and obesity, have a chronic inflammatory component involving both innate and adaptive immunity. Mice lacking the ATP binding cassette (ABC) transporter ABCG1 develop chronic inflammation in the lungs, associated with lipid accumulation (cholesterol, cholesterol ester, and phospholipid) and cholesterol crystal deposition, characteristic of atherosclerotic lesions and PAP. Here we demonstrate that specific lipids, likely oxidized (Ox) phospholipids and/or sterols, elicit a lung-specific immune response in Abcg1−/− mice. Loss of ABCG1 results in increased levels of specific oxysterols, phosphatidylcholines and oxidized phospholipids, including 1-palmitoyl-2-(5’-oxovaleroyl)-sn-glycero-3-phosphocholine (POVPC), in the lungs. Further, we identify a niche-specific increase in natural antibody (NAb)-secreting B-1 B cells in response to this lipid accumulation that is paralleled by increased titers of IgM, IgA and IgG against oxidation specific epitopes such as those on OxLDL and malondialdehyde-modified LDL (MDA-LDL). Finally we identify a cytokine/chemokine signature reflective of increased B cell activation, antibody secretion and homing. Collectively, these data demonstrate that the accumulation of lipids in Abcg1−/− mice induces the specific expansion and localization of B-1 B cells, which secrete NAbs that may help protect against the development of atherosclerosis. Indeed, despite chronic lipid accumulation and inflammation, hyperlipidemic mice lacking ABCG1 develop smaller atherosclerotic lesions compared to controls. These data also suggest that Abcg1−/− mice may represent a new model in which to study the protective functions of B-1 B cells/NAbs, and suggest novel targets for pharmacologic intervention and treatment of disease. PMID:25339664

  18. Study of external dynamic flap loads on a 6 percent B-1B model

    NASA Technical Reports Server (NTRS)

    Seiner, John M.; Manning, James C.; Capone, Francis J.; Pendergraft, Odis C., Jr.

    1991-01-01

    The origin of dynamic pressure loads on external divergent engine nozzle flaps of the B-1B aircraft was investigated in the NASA/LaRC 16 foot transonic tunnel using a 6 percent full span model with powered engine nacelles. External flap dynamic loads and afterbody drag associated with flap removal were measured using this model. Both dry and max. A/B power nozzles were evaluated in this study. As a result of this study, the principal mechanisms responsible for high dynamic external flap loads were determined along with performance penalty associated with flap removal.

  19. Preparation, Purification, and Identification of a Monoclonal Antibody Against NRP2 b1b2 Domain.

    PubMed

    Yang, Yun; Chen, Na; Li, Zhe; Wang, Xian-Jiang; Wang, Sheng-Yu; Tingwu; Luo, Fang-Hong; Yan, Jiang-Hua

    2015-10-01

    First identified as a high-affinity kinase-deficient receptor for class-3 semaphorins and vascular endothelial growth factor (VEGF) families, Neuropilin2 (NRP2) is a transmembrane non-tyrosine-kinase glycoprotein that has a vital function in neuronal patterning. Furthermore, NRP2 expression is often upregulated in cancer tissues and correlated with poor prognosis. In the present study, we report the establishment of a monoclonal antibody specific for NRP2b1b2 domain (NRP2 MAb) through hybridoma method. NRP2 MAb is measured to have a titer of 5.12 × 10(5) against NRP2b1b2 in indirect ELISA. Western blotting, flow cytometry, and immunofluorescence analysis indicate that NRP2 MAb can combine full-length NRP2 in LoVo and SW480 cells. Besides helping further understand NRP2-related pathological mechanisms and cell-signaling pathways, NRP2 MAb may act as a therapeutic agent for cancer in the future. PMID:26492624

  20. Characterizing Dust and Ice Toward Protostars in the Orion Molecular Cloud Complex

    NASA Astrophysics Data System (ADS)

    Poteet, Charles Allen

    Protostars are young stars in the process of accreting infalling envelopes of gas and dust which are transported from the diffuse interstellar medium through gravitational collapse. Although the envelopes are commonly thought to be comprised of cold, pristine material from the interstellar medium, recent space-based studies suggest that protostellar envelopes of low- and high-mass protostars contain thermally processed dust and ice. Unlike the envelope material from luminous, massive protostars, where dust and ice are subject to processing by direct stellar irradiation, thermally processed materials in low-mass protostars may be the consequence of accretion-driven outbursts, shocks in protostellar outflows, or transport of materials from the inner disk to the envelope by outflows and winds. We present an analysis of mid-infrared spectra of a large sample of protostars from the Orion Molecular Cloud complex, the most active region of star formation within the nearest 500 pc. The spectra, obtained with the Infrared Spectrograph onboard the Spitzer Space Telescope , reveal strong silicate and solid molecular absorption bands. Using spectral decomposition analyses to determine the dust and ice composition toward the protostars, we find that the amorphous silicate composition is more dominated by amorphous pyroxene than dust in the Galactic diffuse interstellar medium, and that the mass fraction of amorphous pyroxene varies between protostars. Toward the perplexing protostar HOPS-68, we report the first unambiguous detection of (1) crystalline silicate absorption in a cold, infalling protostellar envelope and (2) highly processed carbon dioxide ice mantles. Moreover, we find evidence for crystalline silicate absorption towards two additional protostars. These results provide strong evidence that dust and ice delivered to planet-forming disks around low-mass stars in the protostellar phase may be processed by feedback from the central protostar.

  1. Protostars and Planets VI

    NASA Astrophysics Data System (ADS)

    Beuther, Henrik; Klessen, Ralf S.; Dullemond, Cornelis P.; Henning, Thomas

    The Protostars and Planets book and conference series has been a long-standing tradition that commenced with the first meeting led by Tom Gehrels and held in Tucson, Arizona, in 1978. The goal then, as it still is today, was to bridge the gap between the fields of star and planet formation as well as the investigation of planetary systems and planets. As Tom Gehrels stated in the preface to the first Protostars and Planets book, "Cross-fertilization of information and understanding is bound to occur when investigators who are familiar with the stellar and interstellar phases meet with those who study the early phases of solar system formation." The central goal remained the same for the subsequent editions of the books and conferences Protostars and Planets II in 1984, Protostars and Planets III in 1990, Protostars and Planets IV in 1998, and Protostars and Planets V in 2005, but has now been greatly expanded by the flood of new discoveries in the field of exoplanet science. The original concept of the Protostars and Planets series also formed the basis for the sixth conference in the series, which took place on July 15-20, 2013. It was held for the first time outside of the United States in the bustling university town of Heidelberg, Germany. The meeting attracted 852 participants from 32 countries, and was centered around 38 review talks and more than 600 posters. The review talks were expanded to form the 38 chapters of this book, written by a total of 250 contributing authors. This Protostars and Planets volume reflects the current state-of-the-art in star and planet formation, and tightly connects the fields with each other. It is structured into four sections covering key aspects of molecular cloud and star formation, disk formation and evolution, planetary systems, and astrophysical conditions for life. All poster presentations from the conference can be found at www.ppvi.org. In the eight years that have passed since the fifth conference and book in the

  2. Wind tunnel study of wake downwash behind A 6% scale model B1-B aircraft

    SciTech Connect

    Strickland, J.H.; Tadios, E.L.; Powers, D.A.

    1990-05-01

    Parachute system performance issues such a turnover and wake recontact may be strongly influenced by velocities induced by the wake of the delivering aircraft, especially if the aircraft is maneuvering at the time of parachute deployment. The effect of the aircraft on the parachute system is a function of the aircraft size, weight, and flight path. In order to provide experimental data for validation of a computer code to predict aircraft wake velocities, a test was conducted in the NASA 14 {times} 22 ft wind tunnel using a 5.78% model of the B-1B strategic bomber. The model was strut mounted through the top of its fuselage by a mechanism which was capable of pitching the model at moderate rates. In this series of tests, the aircraft was pitched at 10{degree}/sec from a cruise angle of attack of 5.3{degree} to an angle of attack of 11{degree} in order to simulate a 2.2g pullup. Data were also taken for the subsequent pitch down sequence back to the cruise angle of attack. Instantaneous streamwise and vertical velocities were measured in the wake at a number of points using a hot wire anemometer. These data have been reduced to the form of downwash coefficients which are a function of the aircraft angle of attack time-history. Unsteady effects are accounted for by use of a wake convection lag-time correlation. 12 refs., 59 figs., 4 tabs.

  3. Protostars in Perseus

    NASA Astrophysics Data System (ADS)

    Barsony, M.; Ward-Thompson, D.; Andre, P.; O'Linger, J.

    1997-12-01

    We present new millimeter, submillimeter, and far-infrared images of three Class 0 protostar systems in Perseus: L1448C, the triple system L1448N, and IRAS 03282+3035. The data were acquired with a 7-element bolometer array on the IRAM 30-m, the common user bolometer, UKT14, on the 15-m James Clerk Maxwell Telescope, and via extensive HIRES processing and modelling of the IRAS data (Aumann, Fowler, & Melnyk 1990). All three sources power bipolar molecular outflows. The spectacular outflow from L1448C is seen in dust emission for the first time at 60, 100, and 1300 microns. The instantaneous outflow mechanical luminosity derived from this emission is found to be a high fraction ( 50%) of the source luminosity, a property recently found to be another distinguishing characteristic of Class 0 protostars, the earliest observable protostellar stage (Bontemps et al. 1996). Extensive HIRES point-source modelling of the 100-micron IRAS emission around IRAS 03282 shows that the emitting dust is co-extensive with the flattened dense gas core, as traced by previous ammonia observations, from which the protostar is forming (Bachiller, Martin-Pintado, & Planesas 1991; Tafalla et al. 1993). References Aumann, H.H., Fowler, J.W., & Melnyk, M. 1990, AJ 99 1674 Bontemps, S., Andre, P., Terebey, S., & Cabrit, S. 1996, A&A 311 858 Bachiller, R., Martin-Pintado, J., & Planesas, P. 1991, A&A 251 639 Tafalla, M, Bachiller, R., Martin-Pintado, J. & M.C.H. Wright 1993, ApJL 415 L139

  4. Waterfalls Around Protostars

    NASA Astrophysics Data System (ADS)

    Mottram, J. C.; van Dishoeck, E. F.; Schmalzl, M.; Kristensen, L. E.; Visser, R.; Hogerheijde, M. R.; Bruderer, S.

    2013-07-01

    Water is uniquely sensitive to motion of any kind within the protostellar environment due to its large Einstein A coefficient. As part of the 'Water in star-forming regions with Herschel' (WISH) survey, infall signatures were detected in the HIFI water spectra observed towards 5 Class 0/I protostars observed. The combination of observations of multiple water transitions and full 1-D non-LTE radiative transfer models of protostellar envelopes provides a self-consistent way to probe the physics and chemistry of infalling envelope material.

  5. Production and Screening of High Yield Avermectin B1b Mutant of Streptomyces avermitilis 41445 Through Mutagenesis

    PubMed Central

    Siddique, Samia; Syed, Quratulain; Adnan, Ahmad; Qureshi, Fahim Ashraf

    2014-01-01

    Background: Secondary metabolite production from wild strains is very low for economical purpose therefore certain strain improvement strategies are required to achieve hundred times greater yield of metabolites. Most important strain improvement techniques include physical and chemical mutagenesis. Broad spectrum mutagenesis through UV irradiation is the most important and convenient physical method. Objectives: The present study was conducted for enhanced production of avermectin B1b from Streptomyces avermitilis 41445 by mutagenesis using ultraviolet (UV) radiation, ethidium bromide (EB), and ethyl methanesulfonate (EMS) as mutagens. Materials and Methods: S. avermitilis DSM 41445 maintained on yeast extract malt extract glucose medium (YMG) was used as inoculum for SM2 fermentation medium. Spores of S. avermitilis DSM 41445 were exposed to UV radiation for physical broad spectrum mutagenesis and to EMS and EB for chemical mutagenesis. For each mutagen, the lethality rate and mutation rate were calculated along with positive mutation rate. Results: Avermectin B1b-hyper-producing mutant, produced using these three different methods, was selected according to the HPLC results. The mutant obtained after 45 minutes of UV radiation to the spores of S. avermitilis 41445, was found to be the best mutant for the enhanced production of avermectin B1b component (254.14 mg/L). Other avermectin B1b-hyper-producing mutants, were obtained from EMS (1 µL/mL) and EB (30 µL/mL) treatments, and yielded 202.63 mg/L and 199.30 mg/L of B1b, respectively. Conclusions: The hereditary stability analysis of the UV mentioning 45 minutes revealed the UV exposure time for mutants and 3 represented the colony taken from the plate irradiated for 45 minutes mutant showed that the production of avermectin B1b remained constant and no reverse mutation occurred after 15 generations. PMID:25147669

  6. Water in the warm inner regions of Class 0 protostars

    NASA Astrophysics Data System (ADS)

    Coutens, Audrey; Jørgensen, Jes K.; Persson, Magnus V.; van Dishoeck, Ewine; vastel, charlotte; Taquet, Vianney; Bottinelli, Sandrine; Caux, Emmanuel; Harsono, Daniel; Lykke, Julie M.

    2015-08-01

    Water plays a key role in many astrophysical environments (star-forming regions, outflows, prestellar cores, comets, asteroids, …) as well as for the emergence of life as we know it. Its detection in the inner regions of low-mass protostars raises the question whether this is similar to the water that is incorporated into comets and asteroids that may deliver it to Earth-like planets. The water deuterium fractionation is very helpful to understand how it forms and evolves. For example, Cleeves et al. (2014) showed that a contribution of water formed in the primordial cloud is necessary to explain the HDO/H2O ratio of the terrestrial oceans. Observations of the deuterated and non-deuterated forms of water at an early stage of star formation may therefore potentially be an important tool to describe the origin of water on Earth.We here present recent interferometric measurements of the distribution and deuteration of water on Solar System scales. During the last few years, a few HDO and H218O lines were observed in the inner regions of Class 0 protostars with interferometers (Jørgensen & van Dishoeck 2010, Codella+2010, Persson+ 2012, 2013, 2014, Taquet+ 2013), which enables estimates of the HDO/H2O ratios. Our recent detection of D2O with the Plateau de Bure interferometer towards the low-mass protostar NGC1333 IRAS2A leads to a surprisingly high D2O/HDO ratio compared with the HDO/H2O ratio (Coutens+ 2014). These results contradict the predictions of current grain surface chemical models and indicate that either an ingredient is missing in our understanding of the surface deuteration process or that both sublimation of grain mantles and water formation at high temperature (T > 230K) take place in the inner regions of protostars. We also present the first results of an ALMA Cycle 2 program (PI: A. Coutens) to target several HDO, H218O and D2O lines at a spatial resolution of ~0.3" (40 AU) toward the nearby protostellar binary IRAS16293-2422. These observations

  7. Kinetics of the B1-B2 phase transition in KCl under rapid compression

    NASA Astrophysics Data System (ADS)

    Lin, Chuanlong; Smith, Jesse S.; Sinogeikin, Stanislav V.; Park, Changyong; Kono, Yoshio; Kenney-Benson, Curtis; Rod, Eric; Shen, Guoyin

    2016-01-01

    Kinetics of the B1-B2 phase transition in KCl has been investigated under various compression rates (0.03-13.5 GPa/s) in a dynamic diamond anvil cell using time-resolved x-ray diffraction and fast imaging. Our experimental data show that the volume fraction across the transition generally gives sigmoidal curves as a function of pressure during rapid compression. Based upon classical nucleation and growth theories (Johnson-Mehl-Avrami-Kolmogorov theories), we propose a model that is applicable for studying kinetics for the compression rates studied. The fit of the experimental volume fraction as a function of pressure provides information on effective activation energy and average activation volume at a given compression rate. The resulting parameters are successfully used for interpreting several experimental observables that are compression-rate dependent, such as the transition time, grain size, and over-pressurization. The effective activation energy (Qeff) is found to decrease linearly with the logarithm of compression rate. When Qeff is applied to the Arrhenius equation, this relationship can be used to interpret the experimentally observed linear relationship between the logarithm of the transition time and logarithm of the compression rates. The decrease of Qeff with increasing compression rate results in the decrease of the nucleation rate, which is qualitatively in agreement with the observed change of the grain size with compression rate. The observed over-pressurization is also well explained by the model when an exponential relationship between the average activation volume and the compression rate is assumed.

  8. Water and complex organic molecules in the warm inner regions of solar-type protostars

    NASA Astrophysics Data System (ADS)

    Coutens, A.; Jørgensen, J. K.; Persson, M. V.; Lykke, J. M.; Taquet, V.; van Dishoeck, E. F.; Vastel, C.; Wampfler, S. F.

    2015-12-01

    Water and complex organic molecules play an important role in the emergence of Life. They have been detected in different types of astrophysical environments (protostars, prestellar cores, outflows, protoplanetary disks, comets, etc). In particular, they show high abundances towards the warm inner regions of protostars, where the icy grain mantles thermally desorb. Can a part of the molecular content observed in these regions be preserved during the star formation process and incorporated into asteroids and comets, that can deliver it to planetary embryos through impacts? By comparison with cometary studies, interferometric observations of solar-type protostars can help to address this important question. We present recent results obtained with the Plateau de Bure interferometer about water deuteration, glycolaldehyde and ethylene glycol towards the low-mass protostar NGC 1333 IRAS2A.

  9. Stellar Properties of Embedded Protostars: Progress and Prospects

    NASA Technical Reports Server (NTRS)

    Greene, Thomas

    2006-01-01

    Until now, high extinctions have prevented direct observation of the central objects of self-embedded, accreting protostars. However, sensitive high dispersion spectrographs on large aperture telescopes have allowed us to begin studying the stellar astrophysical properties of dozens of embedded low mass protostars in the nearest regions of star formation. These high dispersion spectra allow, for the first time, direct measurements of their stellar effective temperatures, surface gravities, rotation velocities, radial velocities (and spectroscopic binarity), mass accretion properties, and mass outflow indicators. Comparisons of the stellar properties with evolutionary models also allow us to estimate masses and constrain ages. We find that these objects have masses similar to those of older, more evolved T Tauri stars, but protostars have higher mean rotation velocities and angular momenta. Most protostars indicate high mass accretion or outflow, but some in Taurus-Auriga appear to be relatively quiescent. These new results are testing, expanding, and refining the standard star formation paradigm, and we explore how to expand this work further.

  10. Far-infrared CO and H2O emission in intermediate-mass protostars

    NASA Astrophysics Data System (ADS)

    Matuszak, M.; Karska, A.; Kristensen, L. E.; Herczeg, G. J.; Tychoniec, Ł.; van Kempen, T. A.; Fuente, A.

    2015-06-01

    Context. Intermediate-mass young stellar objects (YSOs) provide a link to understanding how feedback from shocks and UV radiation scales from low- to high-mass star forming regions. Aims: Our aim is to analyze excitation of CO and H2O in deeply embedded intermediate-mass YSOs and compare it with similar studies on low-mass and high-mass YSOs. Methods: Herschel/PACS spectral maps are analyzed for six YSOs with bolometric luminosities of Lbol ~ 102-103L⊙. The maps cover spatial scales of ~104 AU in several CO and H2O lines located in the ~55-210 μm range. Results: Rotational diagrams of CO show two temperature components at Trot ~ 320 K and Trot ~ 700-800 K, comparable to low- and high-mass protostars probed at similar spatial scales. The diagrams for H2O show a single component at Trot ~ 130 K, as seen in low-mass protostars, and about 100 K lower than in high-mass protostars. Since the uncertainties in Trot are on the same order as the difference between the intermediate and high-mass protostars, we cannot conclude whether the change in rotational temperature occurs at a specific luminosity or whether the change is more gradual from low- to high-mass YSOs. Conclusions: Molecular excitation in intermediate-mass protostars is comparable to the central 103 AU of low-mass protostars and consistent within the uncertainties with the high-mass protostars probed at 3 × 103 AU scales, suggesting similar shock conditions in all those sources. Appendix A is available in electronic form at http://www.aanda.org

  11. 75 FR 3159 - Corporate Reorganizations; Distributions Under Sections 368(a)(1)(D) and 354(b)(1)(B); Correction

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-01-20

    ...) that were published in the Federal Register on Friday, December 18, 2009 (74 FR 67053) providing... Sections 368(a)(1)(D) and 354(b)(1)(B); Correction AGENCY: Internal Revenue Service (IRS), Treasury... final regulations (TD 9475) contain an error that may prove to be misleading and is in need...

  12. B-1 B cell IgM antibody initiates T cell elicitation of contact sensitivity.

    PubMed

    Askenase, P W; Tsuji, R F

    2000-01-01

    Although B-1 B cells have received considerable attention, their actual role in the normal functioning of the immune system is unclear. The hypothesized role of B-1 cell IgM in natural protective immunity is just being established. We have uncovered a separate and novel role for B-1 cell IgM in initiating the elicitation of acquired T cell-dependent contact sensitivity (CS), the prototype of in vivo T cell immunity, early after immunization (within 4 days). The recent recognition of a similarly unanticipated role of B cells in a variety of T cell responses, may indicate that B-1 cell IgM has a broader role in immunity than thought previously. We showed that 24 hr CS responses, and rises in local IFN-gamma levels at 24 hrs later after antigen (Ag) challenge the ears, were absent in pan B cell and antibody deficient mice. The mechanism of B cell involvement in CS-initiation is via local C5a generation early (1-2 hrs) after antigen (Ag) challenge of the ears, in 4 day contact sensitized mice. C5a activates local mast cells to release serotonin (5-HT) and TNF alpha to induce endothelial ICAM-1 and VCAM-1, leading to T cell recruitment. We hypothesized that C5a was generated via complement activation due to antibodies forming local AgAb complexes, and that B-1 cell IgM was involved because isotype switching of B-2 cells to produce C-activating IgG isotypes, could not occur as early as day 4. Indeed, B-1 cell deficient CBA/N-xid mice lacked C5a in 2 hr ear extracts, and had impaired CS ear swelling and elaboration of IFN-gamma at 24 hrs. Importantly, adoptive transfer of purified normal peritoneal B-1 cells, or just i.v. injection of Ag-specific IgM monoclonal antibodies in sensitized xid, restored deficient early C5a and late 24 hr ear swelling. These results suggest that early after Ag challenge, specific B-1 cell IgM, produced at distant sites by prior sensitization, forms AgAb complexes that trigger elaboration of C5a, to activate mast cell release of vasoactive TNF

  13. Estimating the Internal Luminosities of Protostars with SOFIA/FORCAST

    NASA Astrophysics Data System (ADS)

    Huard, Tracy L.; Terebey, Susan

    2016-01-01

    During the last decade, the Spitzer Space Telescope and Herschel Space Telescope enabled large infrared surveys of nearby molecular clouds forming low mass stars. The 70 micron observations obtained by those facilities provide estimates of the internal luminosities of protostars that are reliable to within a factor of 2, in general. Spitzer observations at shorter wavelengths yield estimates that are much less constrained, reliable only to within an order of magnitude, at best. With the Stratospheric Observatory for Infrared Astronomy (SOFIA) routinely operating science flights, this facility may be used to further study protostellar populations. We demonstrate that mid-infrared images obtained with the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST) achieve internal luminosities with reliability comparable to that achieved by 70 micron observations. With its dynamic range and greater angular resolution, FORCAST may be used to characterize protostars that were either saturated or merged with other sources in previous surveys.

  14. Site-Directed Mutagenesis of Human Cytosolic Sulfotransferase (SULT) 2B1b to Phospho-mimetic Ser348Asp Results in an Isoform With Increased Catalytic Activity

    PubMed Central

    Salman, Emily D.; He, Dongning; Runge-Morris, Melissa; Kocarek, Thomas A.; Falany, Charles N.

    2011-01-01

    Human SULT2B1b is distinct from other SULT isoforms due to the presence of unique amino (N)- and carboxy (C)-terminal peptides. Using site-directed mutagenesis, it was determined that phosphorylation of Ser348 was associated with nuclear localization. To investigate the effects of this phosphorylation of Ser348 on activity and cellular localization, an in silico molecular mimic was generated by mutating Ser348 to an Asp. The Asp residue mimics the shape and charge of a phospho-Ser and homology models of SULT2B1b-phospho-S348 and SULT2B1b-S348D suggest a similar significant structural rearrangement in the C-terminal peptide. To evaluate the functional consequences of this post-translational modification and predicted rearrangement, 6His-SULT2B1b-S348D was synthesized, expressed, purified and characterized. The 6His-SULT2B1b-S348D has a specific activity for DHEA sulfation ten-fold higher than recombinant 6His-SULT2B1b (209.6 and 21.8 pmol·min−1·mg−1, respectively). Similar to native SULT2B1b, gel filtration chromatography showed SULT2B1b-S348D was enzymatically active as a homodimer. Stability assays comparing SULT2B1b and SUL2B1b-S348 demonstrated that SULT2B1b is 60% less thermostable than SULT2B1b-348D. The increased stability and sulfation activity allowed for better characterization of the sulfation kinetics for putative substrates as well as the determination of dissociation constants that were difficult to obtain with wild-type (WT) 6His-SULT2B1b. The KDs for DHEA and PAPS binding to 6His-SULT2B1b-S348D were 650 ± 7 nM and 265 ± 4 nM, respectively, whereas KDs for binding of substrates to the WT enzyme could not be determined. Characterization of the molecular mimic SULT2B1b-S348D provides a better understanding for the role of the unique structure of SULT2B1b and its effect on sulfation activity, and has allowed for improved kinetic characterization of the SULT2B1b enzyme. PMID:21855633

  15. Overexpression of SULT2B1b is an independent prognostic indicator and promotes cell growth and invasion in colorectal carcinoma

    PubMed Central

    Hu, Liang; Yang, Guang-Zhen; Zhang, Yu; Feng, Dan; Zhai, Yan-Xia; Gong, Hui; Qi, Chen-Ye; Fu, Hao; Ye, Ming-Ming; Cai, Qing-Ping; Gao, Chun-Fang

    2015-01-01

    Aberrant expression of cytosolic sulfotransferase 2B1b (SULT2B1b) has been reported in several human malignancies. However, the expression pattern and clinical significance of SULT2B1b in colorectal carcinoma (CRC) remains unknown. Real-time quantitative PCR, western blot, and immunohistochemistry analyses were used to determine SULT2B1b expression in CRC clinical samples and CRC-derived cell lines. Kaplan–Meier and Cox proportional regression analyses were used to evaluate the association between SULT2B1b expression and patient survival in two independent cohorts of 485 patients with CRC. Gain- and loss-of-function approaches were employed to investigate the role of SULT2B1b in regulation of CRC cell growth and invasion. We found that SULT2B1b expression was frequently upregulated in CRC clinical samples and CRC-derived cell lines and was significantly correlated with lymph node metastasis and TNM stage in both the training and validation cohorts. Patients with higher intratumoral SULT2B1b expression had a significantly shorter disease-specific survival (DSS) and disease-free survival (DFS) than those with lower expression. Importantly, increased expression of SULT2B1b significantly predicted poor DSS and DFS and was an independent unfavorable prognostic indicator for stage II patients in both cohorts. Functional studies revealed that overexpression of SULT2B1b promoted CRC cell growth and invasion in vitro. Conversely, knockdown of SULT2B1b inhibited these processes. In conclusion, our findings suggest that SULT2B1b expression correlates with disease progression and metastasis and may serve as a novel prognostic biomarker and potential therapeutic target for patients with CRC. PMID:26121319

  16. Star Formation: Chemistry as a Probe of Embedded Protostars

    NASA Astrophysics Data System (ADS)

    Visser, R.

    2013-10-01

    The embedded phase of star formation is the crucial phase where most of the stellar mass is assembled. Velocity-resolved spectra reveal an infalling envelope, bipolar outflows, and perhaps an infant circumstellar disk - all locked together in a cosmic dance of gravitational collapse and magnetic winds. Densities and temperatures change by orders of magnitude as the protostar evolves, driving a chemistry as exotic as it is fascinating. I will review two examples of how to exploit chemistry and molecular spectroscopy to study the physics of low-mass star formation: energetic feedback and episodic accretion.

  17. Tracing the origin of warm water emission through the stages of low-mass star formation

    NASA Astrophysics Data System (ADS)

    Vilhelm Persson, Magnus; Jorgensen, Jes K.; Coutens, Audrey; van Dishoeck, Ewine

    2015-08-01

    Water is a crucial molecule in the physics and chemistry of star- and planet formation, but its evolution from cold cores to disks is still poorly constrained. The gas-phase abundance of water varies between cold and warm regions up to a factor of 105 and this abundance variation makes water an excellent diagnostic of the physical structure in these sources.The origin of the warm water emission in deeply-embedded low-mass protostars is still debated, however. Current options include the innermost envelope (‘hot corino’), heated by the luminosity from the central protostar; a young disk heated by shocks related to ongoing accretion or the warm disk surface layers heated radiatively by the young star. Determining the location and kinematics of the warm water is important because it provides insights into whether water, and the locked up complex organics, actually moves from the outer envelope into the disk, and if so, whether it enters the disk mostly as gas or ice. Evolutionary models suggest that water and complex species enter the disk mostly as ice but this is so far unconfirmed observationally.Thus, in our collaboration we are undertaking a study of warm water in low-mass protostars. So far we have obtained interferometric maps of several isotopologues of water toward four deeply-embedded (i.e. Class 0) low-mass protostars with PdBI and ALMA. The detected water emission is compact toward the Class 0 sources, and a significant source of uncertainty in determining the abundances is the poorly constrained physical structure in the inner regions. Thus we try to constrain this physical structure by fitting simple disk models to the dust continuum visibilities that are left after subtracting a model of the spherical envelope. Furthermore we estimate upper limits to the warm water content toward the Class I protostars TMC-1A and L1527 from observations with PdBI.In this talk I will summarize our ongoing work in tracing the warm water emission through the various

  18. Physical oceanographic processes at candidate dredged-material disposal sites B1B and 1M offshore San Francisco

    SciTech Connect

    Sherwood, C.R.; Denbo, D.W.; Downing, J.P. ); Coats, D.A. )

    1990-10-01

    The US Army Corps of Engineers (USACE), San Francisco District, has identified two candidate sites for ocean disposal of material from several dredging projects in San Francisco Bay. The disposal site is to be designated under Section 103 of the Ocean Dumping Act. One of the specific criteria in the Ocean Dumping Act is that the physical environments of the candidate sites be considered. Toward this goal, the USACE requested that the Pacific Northwest Laboratory conduct a study of physical oceanographic and sediment transport processes at the candidate sites, B1B and 1M. The results of that study are presented in this report. 40 refs., 27 figs., 10 tabs.

  19. High Resolution Near-IR Spectroscopy of Protostars With Large Telescopes

    NASA Technical Reports Server (NTRS)

    Greene, Tom; DeVincenzi, Donald L. (Technical Monitor)

    2001-01-01

    It is now possible to measure absorption spectra of Class I protostars using D greater than or = 8m telescopes equipped with sensitive cryogenic IR spectrographs. Our latest high-resolution (R approx. 20,000) Keck data reveal that Class I protostars are indeed low-mass stars with dwarf-like features. However, they differ from T Tauri stars in that Class I protostars have much higher IR veilings (tau(sub k) greater than or = 1 - 3+) and they are rotating quickly, v sin i greater than 20 km/s. Interestingly, the vast majority of protostellar absorption spectra show stellar - not disk - absorption features. A preliminary H-R diagram suggests that protostellar photospheres may have different physical structures than T Tauri stars, perhaps due to their higher accretion rates.

  20. [Fe II] Emission Tracing Massive, Irradiated Jets from Intermediate-Mass Protostars in the Carina Nebula

    NASA Astrophysics Data System (ADS)

    Reiter, Megan; Smith, Nathan

    2013-07-01

    We present new spectroscopy and HST and ground-based AO imaging of five protostellar jets in the Carina nebula. Near-IR [Fe II] emission traces dense gas in the jet that is self-shielded from Lyman continuum photons from nearby O-type stars, but is excited by non-ionizing FUV photons that penetrate the ionization front within the jet. New near-IR [Fe II] images reveal a substantial mass of dense, neutral gas that is not seen in Halpha emission from these jets, leading to densities and mass-loss rate estimates an order of magnitude higher than those derived from the Halpha emission measure. Higher jet mass-loss rates require higher accretion rates, implying that these jets are driven by intermediate-mass (~2-8 Msun) protostars. For two of the sources, mid-IR luminosities of the driving sources are clearly consistent with intermediate-mass protostars, while the other two driving sources are more deeply embedded and require imaging at longer wavelengths with high spatial resolution to confirm their luminosity. Tangential velocities from new proper motion measurements exceed velocities typical for lower-luminosity sources (100-200 km/s). In addition, these outflows are highly collimated, with opening angles of only a few degrees, similar to low-mass protostars. We propose that these jets reflect essentially the same outflow phenomenon seen in low-mass protostars, but that the collimated atomic jet core is irradiated and rendered observable. Thus, the jets in Carina constitute a new view of collimated jets from intermediate-mass protostars that exists in a feedback dominated environment, and offer strong additional evidence that stars up to ~8 Msun form by the same accretion mechanisms as low-mass stars.

  1. Carbon Chains and Methanol toward Embedded Protostars

    NASA Astrophysics Data System (ADS)

    Graninger, Dawn M.; Wilkins, Olivia H.; Öberg, Karin I.

    2016-03-01

    Large interstellar organic molecules are potential precursors of prebiotic molecules. Their formation pathways and chemical relationships with one another and simpler molecules are therefore of great interest. In this paper we address the relationships between two classes of large organic molecules, carbon chains and saturated complex organic molecules at the early stages of star formation through observations of C4H and CH3OH. We surveyed these molecules with the IRAM 30 m telescope toward 16 deeply embedded low-mass protostars selected from the Spitzer c2d ice survey. We find that CH3OH and C4H are positively correlated, indicating that these two classes of molecules can coexist during the embedded protostellar stage. The C4H/CH3OH gas abundance ratio tentatively correlates with the CH4/CH3OH ice abundance ratio in the same lines of sight. This relationship supports a scenario where carbon chain formation in protostellar envelopes begins with CH4 ice desorption. Based on observations carried out with the IRAM 30 m Telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).

  2. A submillimeter line survey of low-mass protostars: prelude to ALMA and Herschel

    NASA Astrophysics Data System (ADS)

    van Dishoeck, E. F.; Jørgensen, J. K.; Maret, S.; Ceccarelli, C.; Caux, E.; Schöier, F. L.; Castets, A.; Tielens, A. G. G. M.

    2005-01-01

    The results from a single-dish molecular line survey of a set of 18 deeply embedded young stellar objects are summarized. More than 40 lines from 16 different species were observed with the JCMT, Onsala, IRAM 30m and SEST telescopes. The multi-transition data are analyzed using a temperature and density structure derived from models of the dust continuum emission. For the outer envelope (>300 AU), the data indicate a "drop" abundance profile for many species, with normal abundances in the outer- and innermost regions and highly depleted abundances in an intermediate zone. This zone is bounded at the outer edge by the density where the timescale for freeze-out becomes longer than the life-time of the core, and at the inner edge by the evaporation temperature of the species involved. In the innermost envelope (<300 AU), all ices evaporate resulting in jumps in the abundances of complex organic molecules such as CH3OH. A key project for Herschel will be to survey gas-phase water in these objects, whose abundance shows extreme variations with temperature. ALMA will be able to directly image the chemical variations throughout the envelope and zoom in on the inner hot core and protoplanetary disks on scales on tens of AU.

  3. THE MAGNETIC FIELD MORPHOLOGY OF THE CLASS 0 PROTOSTAR L1157-mm

    SciTech Connect

    Stephens, Ian W.; Looney, Leslie W.; Kwon, Woojin; Crutcher, Richard M.; Hull, Charles L. H.; Plambeck, Richard L.; Chapman, Nicholas; Novak, Giles; Matthews, Tristan; Davidson, Jacqueline; Vaillancourt, John E.; Shinnaga, Hiroko

    2013-05-20

    We present the first detection of polarization around the Class 0 low-mass protostar L1157-mm at two different wavelengths. We show polarimetric maps at large scales (10'' resolution at 350 {mu}m) from the SHARC-II Polarimeter and at smaller scales (1.''2-4.''5 at 1.3 mm) from the Combined Array for Research in Millimeter-wave Astronomy (CARMA). The observations are consistent with each other and show inferred magnetic field lines aligned with the outflow. The CARMA observations suggest a full hourglass magnetic field morphology centered about the core; this is only the second well-defined hourglass detected around a low-mass protostar to date. We apply two different methods to CARMA polarimetric observations to estimate the plane-of-sky magnetic field magnitude, finding values of 1.4 and 3.4 mG.

  4. Powerful jets driven by intermediate-mass protostars in the Carina Nebula

    NASA Astrophysics Data System (ADS)

    Reiter, Megan; Smith, N.

    2014-01-01

    The Carina nebula hosts the largest known population of powerful HH jets driven by intermediate-mass stars in a single region. These jets are externally irradiated by dozens of O-type stars in Carina that illuminate unshocked material in the jet, allowing for a more complete census of the mass-loss. Despite the strong incident ionizing radiation, portions of these jets remain neutral. Near-IR [Fe II] images reveal dense, neutral gas that was not seen in previous studies of Hα emission. We show that near-IR [Fe II] emitting gas must be self-shielded from Lyman continuum photons, regardless of its excitation mechanism (shocks, FUV radiation, or both). High densities are required for the survival of Fe+ amid the strong Lyman continuum luminosity from Tr14, raising estimates of the mass-loss rates by an order of magnitude. New proper motion measurements using Halpha images with a ~4.25 year baseline reveal tangential velocities of >200 km/s, in some cases exceeding velocities typical for jets from low-mass stars. In addition, these outflows are highly collimated, with opening angles of only a few degrees, similar to low-mass protostars. We propose that these jets reflect essentially the same outflow phenomenon seen in low-mass protostars, but that the collimated atomic jet core is irradiated and rendered observable. Thus, the irradiated jets in Carina constitute a new view of jets from intermediate-mass protostars that demonstrate that they are as collimated as their low-mass counterparts, but support higher densities and velocities, leading to higher mass-loss rates. This scaling of phenomena seen in low-mass star formation offers strong additional evidence that stars up to ~8 Msun form by the same accretion mechanism as low-mass stars.

  5. Constraining the Abundances of Complex Organics in the Inner Regions of Solar-type Protostars

    NASA Astrophysics Data System (ADS)

    Taquet, Vianney; López-Sepulcre, Ana; Ceccarelli, Cecilia; Neri, Roberto; Kahane, Claudine; Charnley, Steven B.

    2015-05-01

    The high abundances of Complex Organic Molecules (COMs) with respect to methanol, the most abundant COM, detected toward low-mass protostars, tend to be underpredicted by astrochemical models. This discrepancy might come from the large beam of the single-dish telescopes, encompassing several components of the studied protostar, commonly used to detect COMs. To address this issue, we have carried out multi-line observations of methanol and several COMs toward the two low-mass protostars NGC 1333-IRAS 2A and -IRAS 4A with the Plateau de Bure interferometer at an angular resolution of 2″, resulting in the first multi-line detection of the O-bearing species glycolaldehyde and ethanol and of the N-bearing species ethyl cyanide toward low-mass protostars other than IRAS 16293. The high number of detected transitions from COMs (more than 40 methanol transitions for instance) allowed us to accurately derive the source size of their emission and the COM column densities. The COM abundances with respect to methanol derived toward IRAS 2A and IRAS 4A are slightly, but not substantitally, lower than those derived from previous single-dish observations. The COM abundance ratios do not vary significantly with the protostellar luminosity, over five orders of magnitude, implying that low-mass hot corinos are quite chemically rich as high-mass hot cores. Astrochemical models still underpredict the abundances of key COMs, such as methyl formate or di-methyl ether, suggesting that our understanding of their formation remains incomplete.

  6. A model for the transcriptional regulation of the CYP2B1/B2 gene in rat liver.

    PubMed Central

    Prabhu, L; Upadhya, P; Ram, N; Nirodi, C S; Sultana, S; Vatsala, P G; Mani, S A; Rangarajan, P N; Surolia, A; Padmanaban, G

    1995-01-01

    The phenobarbitone-responsive minimal promoter has been shown to lie between nt -179 and nt + 1 in the 5' (upstream) region of the CYP2B1/B2 gene in rat liver, on the basis of the drug responsiveness of the sequence linked to human growth hormone gene as reporter and targeted to liver as an asialoglycoprotein-DNA complex in vivo. Competition analyses of the nuclear protein-DNA complexes formed in gel shift assays with the positive (nt -69 to -98) and negative (nt -126 to -160) cis elements (PE and NE, respectively) identified within this region earlier indicate that the same protein may be binding to both the elements. The protein species purified on PE and NE affinity columns appear to be identical based on SDS/PAGE analysis, where it migrates as a protein of 26-28 kDa. Traces of a high molecular weight protein (94-100 kDa) are also seen in the preparation obtained after one round of affinity chromatography. The purified protein stimulates transcription of a minigene construct containing the 179 nt on the 5' side of the CYP2B1/B2 gene linked to the I exon in a cell-free system from liver nuclei. The purified protein can give rise to all the three complexes (I, II, and III) with the PE, just as the crude nuclear extract, under appropriate conditions. Manipulations in vitro indicate that the NE has a significantly higher affinity for the dephosphorylated form than for the phosphorylated form of the protein. The PE binds both forms. Phenobarbitone treatment of the animal leads to a significant increase in the phosphorylation of the 26- to 28-kDa and 94-kDa proteins in nuclear labeling experiments followed by isolation on a PE affinity column. We propose that the protein binding predominantly to the NE in the dephosphorylated state characterizes the basal level of transcription of the CYP2B1/B2 gene. Phenobarbitone treatment leads to phosphorylation of the protein, shifting the equilibrium toward binding to the PE. This can promote interaction with an upstream

  7. A model for the transcriptional regulation of the CYP2B1/B2 gene in rat liver.

    PubMed

    Prabhu, L; Upadhya, P; Ram, N; Nirodi, C S; Sultana, S; Vatsala, P G; Mani, S A; Rangarajan, P N; Surolia, A; Padmanaban, G

    1995-10-10

    The phenobarbitone-responsive minimal promoter has been shown to lie between nt -179 and nt + 1 in the 5' (upstream) region of the CYP2B1/B2 gene in rat liver, on the basis of the drug responsiveness of the sequence linked to human growth hormone gene as reporter and targeted to liver as an asialoglycoprotein-DNA complex in vivo. Competition analyses of the nuclear protein-DNA complexes formed in gel shift assays with the positive (nt -69 to -98) and negative (nt -126 to -160) cis elements (PE and NE, respectively) identified within this region earlier indicate that the same protein may be binding to both the elements. The protein species purified on PE and NE affinity columns appear to be identical based on SDS/PAGE analysis, where it migrates as a protein of 26-28 kDa. Traces of a high molecular weight protein (94-100 kDa) are also seen in the preparation obtained after one round of affinity chromatography. The purified protein stimulates transcription of a minigene construct containing the 179 nt on the 5' side of the CYP2B1/B2 gene linked to the I exon in a cell-free system from liver nuclei. The purified protein can give rise to all the three complexes (I, II, and III) with the PE, just as the crude nuclear extract, under appropriate conditions. Manipulations in vitro indicate that the NE has a significantly higher affinity for the dephosphorylated form than for the phosphorylated form of the protein. The PE binds both forms. Phenobarbitone treatment of the animal leads to a significant increase in the phosphorylation of the 26- to 28-kDa and 94-kDa proteins in nuclear labeling experiments followed by isolation on a PE affinity column. We propose that the protein binding predominantly to the NE in the dephosphorylated state characterizes the basal level of transcription of the CYP2B1/B2 gene. Phenobarbitone treatment leads to phosphorylation of the protein, shifting the equilibrium toward binding to the PE. This can promote interaction with an upstream

  8. The puzzling deuteration of methanol in low- to high-mass protostars

    NASA Astrophysics Data System (ADS)

    Ratajczak, A.; Taquet, V.; Kahane, C.; Ceccarelli, C.; Faure, A.; Quirico, E.

    2011-04-01

    Context. The current theory of methanol deuteration on interstellar grains predicts that the abundance ratio of the singly deuterated isotopologues [CH2DOH]/[CH3OD] should always be ~3. In warm regions where grain mantles have sublimated, gaseous methanol is detectable via its rotational transitions. In previous observational studies, the gas-phase [CH2DOH]/[CH3OD] ratio was measured and found to be significantly larger than 3 in low-mass protostars and close to 1 in the Orion IRc2 massive hot core. Aims: We present new measurements of the gas-phase [CH2DOH]/[CH3OD] ratio in two additional high-mass protostars, as well as in two intermediate-mass protostars, to either confirm or exclude the dependence of this ratio on the mass of the protostar. Methods: The observations were carried out using the IRAM-30 m telescope. Several rotational lines of each isotopologue were detected toward the intermediate-mass protostars, while only CH3OD lines were detected in the massive hot cores. The ratio [CH2DOH]/[CH3OD] (or its upper limit) was computed from both the averaged column densities and directly from line flux ratios. Results: Our results confirm that the [CH2DOH]/[CH3OD] ratio is substantially lower in massive hot cores than in (low-mass) hot-corinos, by typically one order of magnitude. Furthermore, they suggest that intermediate-mass protostars have similar properties to low-mass protostars. Conclusions: The measured [CH2DOH]/[CH3OD] ratios are inconsistent with the current theory of methanol deuteration, independently of the mass of the source. While the large ratios measured in low- and intermediate-mass sources can be explained qualitatively by various selective depletion mechanisms, the small ratios (<2) measured toward massive hot cores are puzzling. A revision of the deuterium chemistry in hot cores is suggested. Table A.1 is only available in electronic form at http://www.aanda.org

  9. Cataloging the Youngest Protostars in NGC2264

    NASA Astrophysics Data System (ADS)

    Barnes, Jonathan; Brown, Arianna; Terebey, Susan; CSI2264

    2016-06-01

    Protostars are young stars in their earliest stages of development. We can determine the current stage of development of a young star depending on its relative brightness at varying wavelengths. Protostars are brightest at far-infrared wavelengths, typically peaking at 70-100um. A previous catalog of young stars in NGC 2264 is based on Spitzer data with 24um being the longest available wavelength data. Herschel data at 70um was used to improve the census of protostars. We found 11 new class 0 and 1 protostar candidates that were previously not found in the Spitzer catalog and are bright at 70um. We describe the properties of these candidates.

  10. SULT2B1b Sulfotransferase: Induction by Vitamin D Receptor and Reduced Expression in Prostate Cancer

    PubMed Central

    Seo, Young-Kyo; Mirkheshti, Nooshin; Song, Chung S.; Kim, Soyoung; Dodds, Sherry; Ahn, Soon C.; Christy, Barbara; Mendez-Meza, Rosario; Ittmann, Michael M.; Abboud-Werner, Sherry

    2013-01-01

    An elevated tumor tissue androgen level, which reactivates androgen receptor in recurrent prostate cancer, arises from the intratumor synthesis of 5α-dihydrotestosterone through use of the precursor steroid dehydroepiandrosterone (DHEA) and is fueled by the steroidogenic enzymes 3β-hydroxysteroid dehydrogenase (3β-HSD1), aldoketoreductase (AKR1C3), and steroid 5-alpha reductase, type 1 (SRD5A1) present in cancer tissue. Sulfotransferase 2B1b (SULT2B1b) (in short, SULT2B) is a prostate-expressed hydroxysteroid SULT that converts cholesterol, oxysterols, and DHEA to 3β-sulfates. DHEA metabolism involving sulfonation by SULT2B can potentially interfere with intraprostate androgen synthesis due to reduction of free DHEA pool and, thus, conversion of DHEA to androstenedione. Here we report that in prostatectomy specimens from treatment-naive patients, SULT2B expression is markedly reduced in malignant tissue (P < .001, Mann-Whitney U test) compared with robust expression in adjacent nonmalignant glands. SULT2B was detected in formalin-fixed specimens by immunohistochemistry on individual sections and tissue array. Immunoblotting of protein lysates of frozen cancer and matched benign tissue confirmed immunohistochemistry results. An in-house–developed rabbit polyclonal antibody against full-length human SULT2B was validated for specificity and used in the analyses. Ligand-activated vitamin D receptor induced the SULT2B1 promoter in vivo in mouse prostate and increased SULT2B mRNA and protein levels in vitro in prostate cancer cells. A vitamin D receptor/retinoid X receptor-α–bound DNA element (with a DR7 motif) mediated induction of the transfected SULT2B1 promoter in calcitriol-treated cells. SULT2B knockdown caused an increased proliferation rate of prostate cancer cells upon stimulation by DHEA. These results suggest that the tumor tissue SULT2B level may partly control prostate cancer growth, and its induction in a therapeutic setting may inhibit disease

  11. Identifying the Low-Luminosity Population of Embedded Protostars in the c2d Observations of Clouds and Cores

    NASA Astrophysics Data System (ADS)

    Dunham, Michael M.; Crapsi, Antonio; Evans, Neal J., II; Bourke, Tyler L.; Huard, Tracy L.; Myers, Philip C.; Kauffmann, Jens

    2008-11-01

    We present the results of a search for all embedded protostars with internal luminosities <=1.0 L⊙ in the full sample of nearby, low-mass star-forming regions surveyed by the Spitzer Space Telescope Legacy Project "From Molecular Cores to Planet Forming Disks" (c2d). The internal luminosity of a source, Lint, is the luminosity of the central source and excludes luminosity arising from external heating. On average, the Spitzer c2d data are sensitive to embedded protostars with Lint >= 4 × 10-3(d/140 pc)2 L⊙, a factor of 25 better than the sensitivity of the Infrared Astronomical Satellite (IRAS) to such objects. We present a set of selection criteria used to identify candidates from the Spitzer data and examine complementary data to decide whether each candidate is truly an embedded protostar. We find a tight correlation between the 70 μm flux and internal luminosity of a protostar, an empirical result based on both observations and detailed two-dimensional radiative transfer models of protostars. We identify 50 embedded protostars with Lint <= 1.0 L⊙ 15 have Lint <= 0.1 L⊙. The intrinsic distribution of source luminosities increases to lower luminosities. While we find sources down to the above sensitivity limit, indicating that the distribution may extend to luminosities lower than probed by these observations, we are able to rule out a continued rise in the distribution below Lint = 0.1 L⊙. Between 75% and 85% of cores classified as starless prior to being observed by Spitzer remain starless to our luminosity sensitivity; the remaining 15%-25% harbor low-luminosity, embedded protostars. We compile complete spectral energy distributions for all 50 objects and calculate standard evolutionary signatures (Lbol, Tbol, and Lbol/Lsmm) and argue that these objects are inconsistent with the simplest picture of star formation, wherein mass accretes from the core onto the protostar at a constant rate.

  12. Chemistry in low-mass protostellar and protoplanetary regions

    PubMed Central

    van Dishoeck, Ewine F.

    2006-01-01

    When interstellar clouds collapse to form new stars and planets, the surrounding gas and dust become part of the infalling envelopes and rotating disks, thus providing the basic material from which new solar systems are formed. Instrumentation to probe the chemistry in low-mass star-forming regions has only recently become available. The results of a systematic program to study the abundances in solar-mass protostellar and protoplanetary regions are presented. Surveys at submillimeter and infrared wavelengths reveal a rich chemistry, including simple and complex (organic) gases, ices, polycyclic aromatic hydrocarbons, and silicates. Each of these species traces different aspects of the physical and chemical state of the objects as they evolve from deeply embedded protostars to pre-main sequence stars with planet-forming disks. Quantitative information on temperatures, densities, and abundances is obtained through molecular excitation and radiative transfer models as well as from analysis of solid-state line profiles. The chemical characteristics are dominated by freeze-out in the coldest regions and ice evaporation in the warmer zones. In the surface layers of disks, UV radiation controls the chemistry. The importance of complementary laboratory experiments and calculations to obtain basic molecular data is emphasized. PMID:16894165

  13. Chemistry in low-mass protostellar and protoplanetary regions.

    PubMed

    van Dishoeck, Ewine F

    2006-08-15

    When interstellar clouds collapse to form new stars and planets, the surrounding gas and dust become part of the infalling envelopes and rotating disks, thus providing the basic material from which new solar systems are formed. Instrumentation to probe the chemistry in low-mass star-forming regions has only recently become available. The results of a systematic program to study the abundances in solar-mass protostellar and protoplanetary regions are presented. Surveys at submillimeter and infrared wavelengths reveal a rich chemistry, including simple and complex (organic) gases, ices, polycyclic aromatic hydrocarbons, and silicates. Each of these species traces different aspects of the physical and chemical state of the objects as they evolve from deeply embedded protostars to pre-main sequence stars with planet-forming disks. Quantitative information on temperatures, densities, and abundances is obtained through molecular excitation and radiative transfer models as well as from analysis of solid-state line profiles. The chemical characteristics are dominated by freeze-out in the coldest regions and ice evaporation in the warmer zones. In the surface layers of disks, UV radiation controls the chemistry. The importance of complementary laboratory experiments and calculations to obtain basic molecular data is emphasized. PMID:16894165

  14. Physical oceanographic processes at candidate dredged-material disposal sites B1B and 1M offshore San Francisco

    SciTech Connect

    Sherwood, C.R.; Denbo, D.W.; Downing, J.P. ); Coats, D.A. )

    1990-10-01

    The US Army Corps of Engineers (USACE), San Francisco District, has identified two candidate sites for ocean disposal of material from several dredging projects in San Francisco Bay. The disposal site is to be designated under Section 103 of the Ocean Dumping Act. One of the specific criteria in the Ocean Dumping Act is that the physical environments of the candidate sites be considered. Toward this goal, the USACE requested that the Pacific Northwest Laboratory conduct studies of physical oceanographic and sediment transport processes at the candidate sites. Details of the methods and complete listing or graphical representation of the results are contained in this second volume of the two-volume report. Appendix A describes the methods and results of a pre-disposal bathymetric survey of Site B1B, and provides an analysis of the accuracy and precision of the survey. Appendix B describes the moorings and instruments used to obtain physical oceanographic data at the candidate sites, and also discussed other sources of data used in the analyses. Techniques used to analyze the formation, processed data, and complete results of various analyses are provided in tabular and graphical form. Appendix C provides details of the sediment transport calculations. Appendix D describes the format of the archived current meter data, which is available through the National Oceanographic Data Center. 43 refs., 54 figs., 58 tabs.

  15. Uncommon occurrence ratios of aflatoxin B1, B 2, G 1, and G 2 in maize and groundnuts from Malawi.

    PubMed

    Matumba, Limbikani; Sulyok, Michael; Njoroge, Samuel M C; Njumbe Ediage, Emmanuel; Van Poucke, Christof; De Saeger, Sarah; Krska, Rudolf

    2015-02-01

    We report an unusual aflatoxin profile in maize and groundnuts from Malawi, with aflatoxin G1 found routinely at equal or even higher levels than aflatoxin B1. Aflatoxin B1 (AFB1) ratio in a contaminated sample is generally greater than 50% of total aflatoxin (sum of aflatoxin B1, B2, G1, and G2). In Malawi, the aflatoxin occurrence ratios were determined by examining LC-MS/MS and HPLC fluorescence detection (FLD) data of 156 naturally contaminated raw maize and 80 groundnut samples collected in 2011 and 2012. Results showed that natural aflatoxin occurrence ratio differed. In 47% of the samples, the concentration of AFG1 was higher than that of AFB1. The mean concentration percentages of AFB1/AFB2/AFG1/AFG2 in reference to total aflatoxins were found to be 47:5:43:5%, respectively. The AFG1 and AFB1 50/50 trend was observed in maize and groundnuts and was consistent for samples collected in both years. If the AFB1 measurement was used to check compliance of total aflatoxin regulatory limit set at 10, 20, 100, and 200 μg/kg with an assumption that AFB1≥50% of the total aflatoxin content, 8, 13, 24, and 26% false negative rates would have occurred respectively. It is therefore important for legislation to consider total aflatoxins rather than AFB1 alone. PMID:25194830

  16. The pressure induced B1-B2 phase transition of alkaline halides and alkaline earth chalcogenides. A first principles investigation

    SciTech Connect

    Potzel, Oliver; Taubmann, Gerhard

    2011-05-15

    In this work, we considered the pressure induced B1-B2 phase transition of AB compounds. The DFT calculations were carried out for 11 alkaline halides, 11 alkaline earth chalcogenides and the lanthanide pnictide CeP. For both the B1 and the B2 structures of each compound, the energy was calculated as a function of the cell volume. The transition pressure, the bulk moduli and their pressure derivatives were obtained from the corresponding equations of state. The transition path of the Buerger mechanism was described using roots of the transition matrix. We correlated the computed enthalpies of activation to some structure defining properties of the compounds. A fair correlation to Pearsons hardness of the ions was observed. -- Graphical abstract: Pressure induced transition from the B1 structure (left) via the transition state (middle) to the B2 structure (right). Display Omitted highlights: > Pressure induced phase transitions in AB compounds were considered. > Alkaline halides and alkaline earth chalcogenides were treated. > DFT calculations with periodic boundary conditions were applied. > The transition path was described by roots of the transition matrix. > The enthalpy of activation was calculated for numerous compounds.

  17. Molecular Anions in Protostars, Prestellar Cores and Dark Clouds

    NASA Technical Reports Server (NTRS)

    Cordiner, Martin; Charnley, Steven; Buckle, Jane; Wash, Catherine; Millar, Tom

    2011-01-01

    From our recent survey work using the Green Bank Telescope, microwave emission lines from the hydrocarbon anion C6H(-) and its parent neutral C6H have been detected in six new sources. Using HC3N = 10(exp -9) emission maps, we targeted the most carbon-chain-rich sources for our anion survey, which included the low-mass Class 0 protostar L1251A-IRS3, the prestellar cores L1389-SMM1 and L1512, and the interstellar clouds Ll172A, TMC-1C and L1495B. Derived [C6H(-)]/[C6H] anion-to-neutral ratios are approximately 1-10. The greatest C6H(-) column densities are found in the quiescent clouds TMC-1C and L1495B, but the anion-to-neutral ratios are greatest in the prestellar cores and protostars. These results are interpreted in terms of the physical and chemical properties of the sources, and the implications for molecular cloud chemistry are discussed.

  18. Evolution of Massive Protostars Via Disk Accretion

    NASA Astrophysics Data System (ADS)

    Hosokawa, Takashi; Yorke, Harold W.; Omukai, Kazuyuki

    2010-09-01

    Mass accretion onto (proto-)stars at high accretion rates \\dot{M}_* > 10^{-4} M_{⊙} yr^{-1} is expected in massive star formation. We study the evolution of massive protostars at such high rates by numerically solving the stellar structure equations. In this paper, we examine the evolution via disk accretion. We consider a limiting case of "cold" disk accretion, whereby most of the stellar photosphere can radiate freely with negligible backwarming from the accretion flow, and the accreting material settles onto the star with the same specific entropy as the photosphere. We compare our results to the calculated evolution via spherically symmetric accretion, the opposite limit, whereby the material accreting onto the star contains the entropy produced in the accretion shock front. We examine how different accretion geometries affect the evolution of massive protostars. For cold disk accretion at 10-3 M sun yr-1, the radius of a protostar is initially small, R *sime a few R sun. After several solar masses have accreted, the protostar begins to bloat up and for M * ~= 10 M sun the stellar radius attains its maximum of 30-400 R sun. The large radius ~100 R sun is also a feature of spherically symmetric accretion at the same accreted mass and accretion rate. Hence, expansion to a large radius is a robust feature of accreting massive protostars. At later times, the protostar eventually begins to contract and reaches the zero-age main sequence (ZAMS) for M * ~= 30 M sun, independent of the accretion geometry. For accretion rates exceeding several 10-3 M sun yr-1, the protostar never contracts to the ZAMS. The very large radius of several hundreds R sun results in the low effective temperature and low UV luminosity of the protostar. Such bloated protostars could well explain the existence of bright high-mass protostellar objects, which lack detectable H II regions.

  19. Characterizing the small scale structures in the earliest stages of low-mass star formation

    NASA Astrophysics Data System (ADS)

    Vilhelm Persson, Magnus; van Dishoeck, Ewine; Tobin, John; Harsono, Daniel; Jørgensen, Jes K.

    2015-08-01

    In deeply-embedded low-mass protostars, the density and temperature distribution in the inner few hundred AU’s are poorly constrained. In sources where the envelope is less massive, i.e. the Class I stage, disks with Keplerian rotation have been inferred using C18O lines. However, constraining the various disk characteristics turns out to be difficult even in this case. Continuum and molecular line observations of optically thin tracers at very high sensitivity and resolution are needed to constrain the density, temperature and kinematics. Ultimately the assumed structure affects the determination of molecular abundances.We are attempting to model high-resolution dust continuum radio-interferometric observations of a few deeply-embedded low-mass protostars with a power-law disk model embedded in a spherical envelope.We model the interferometric visibilities taken with either the Plateau de Bure Interferometer or the ALMA telescope, probing scales down to a few tens of AU in some cases. Given the assumptions, the study shows disk sizes in the deeply-embedded phase that could be slightly larger than typical found in the more evolved Class I sources. The fitting also highlights that models for the physical structure of the inner envelope, on 500-2000 AU scales, needs to be improved. With future high sensitivity observations, we could potentially also be able to constrain any vertical density and temperature structure. In this poster I will present the

  20. Tracing Massive Protostellar Jets from Intermediate-Mass Protostars in the Carina Nebula

    NASA Astrophysics Data System (ADS)

    Reiter, A.

    2014-09-01

    We present new spectroscopy and imaging of four protostellar jets in the Carina nebula. Near-IR [Fe II] emission traces dense gas in the jet that is self-shielded from Lyman continuum photons from nearby O-type stars. New near-IR [Fe II] images reveal a substantial mass of dense, neutral gas that is not seen in the Halpha emission from these jets, leading to densities and mass-loss rate estimates an order of magnitude larger than those derived from the Halpha emission measure. Higher jet mass-loss rates require higher accretion rates, implying that these jets are driven by intermediate-mass (around 2 - 8 solar masses) protostars. Velocities from new proper motion and spectroscopic measurements fall among the velocities typically measured in lower-luminosity sources (100 - 200 km/s). We propose that these jets reflect essentially the same outflow phenomenon seen in low-mass protostars, but that the collimated atomic jet core is irradiated and rendered observable. Thus, the jets in Carina constitute a new view of collimated jets from intermediate-mass protostars that exist in a feedback-dominated environment, and offer strong additional evidence that stars up to 8 solar masses form by the same accretion mechanisms as low-mass stars.

  1. Determination of aflatoxins B1, B2, G1, and G2 in olive oil, peanut oil, and sesame oil.

    PubMed

    Bao, Lei; Trucksess, Mary W; White, Kevin D

    2010-01-01

    Edible oils are consumed directly, and used as ingredients in food, soaps, and skin products. However, oils such as olive oil, peanut oil, and sesame oil could be contaminated with aflatoxins, which are detrimental to human and animal health. A method using immunoaffinity column cleanup with RPLC separation and fluorescence detection (FLD) for determination of aflatoxins (AF) B1, B2, G1, and G2 in olive oil, peanut oil, and sesame oil was developed and validated. Test samples were extracted with methanol-water (55 + 45, v/v). After shaking and centrifuging, the lower layer was filtered, diluted with water, and filtered through glass microfiber filter paper. The filtrate was then passed through an immunoaffinity column, and the toxins were eluted with methanol. The toxins were then subjected to RPLC/FLD analysis after postcolumn UV photochemical derivatization. The accuracy and repeatability characteristics of the method were determined. Recoveries of AFB1 spiked at levels from 1.0 to 10.0 microg/kg in olive oil, peanut oil, and sesame oil ranged from 82.9 to 98.6%. RSDs ranged from 0.6 to 8.9%. HorRat values were < 0.2 for all of the matrixes tested. Recoveries of AF spiked at levels from 2.0 to 20.0 microg/kg ranged from 87.7 to 102.2%. RSDs ranged from 1.3 to 12.6%. HorRat values were < 0.4 for all of the matrixes tested. LC/MS/MS with multiple-reaction monitoring was used to confirm the identities of aflatoxins in a naturally contaminated peanut oil. PMID:20629398

  2. New analytical techniques for mycotoxins in complex organic matrices. [Aflatoxins B1, B2, G1, and G2

    SciTech Connect

    Bicking, M.K.L.

    1982-07-01

    Air samples are collected for analysis from the Ames Solid Waste Recovery System. The high level of airborne fungi within the processing area is of concern due to the possible presence of toxic mycotoxins, and carcinogenic fungal metabolites. An analytical method has been developed to determine the concentration of aflatoxins B1, B2, G1, and G2 in the air of the plant which produces Refuse Derived Fuel (RDF). After extraction with methanol, some components in the matrix are precipitated by dissolving the sample in 30% acetonitrile/chloroform. An aliquot of this solution is injected onto a Styragel column where the sample components undergo simultaneous size exclusion and reverse phase partitioning. Additional studies have provided a more thorough understanding of solvent related non-exclusion effects on size exclusion gels. The Styragel column appears to have a useable lifetime of more than six months. After elution from Styragel, the sample is diverted to a second column containing Florisil which has been modified with oxalic acid and deactivated with water. Aflatoxins are eluted with 5% water/acetone. After removal of this solvent, the sample is dissolved in 150 ..mu..L of a spotting solvent and the entire sample applied to a thin layer chromatography (TLC) plate using a unique sample applicator developed here. The aflatoxins on the TLC plate are analyzed by laser fluorescence. A detection limit of 10 pg is possible for aflatoxin standards using a nitrogen laser as the excitation source. Sample concentrations are determined by comparing with an internal standard, a specially synthesized aflatoxin derivative. In two separate RDF samples, aflatoxin B1 was found at levels of 6.5 and 17.0 ppB. The analytical method has also proven useful in the analysis of contaminated corn and peanut meal samples. 42 figures, 8 tables.

  3. Oxysterol Sulfation by SULT2B1b Suppresses LXR/SREBP-1c Signaling Pathway and Reduces Serum and Hepatic Lipids in Mouse Models of NAFLD

    PubMed Central

    Bai, Qianming; Zhang, Xin; Xu, Leyuan; Kakiyama, Genta; Heuman, Douglas; Sanyal, Arun; Pandak, William M.; Yin, Lianhua; Xie, Wen; Ren, Shunlin

    2012-01-01

    Background Cytosolic sulfotransferase (SULT2B1b) catalyzes oxysterol sulfation. 5-cholesten-3β-25-diol-3-sulfate (25HC3S), one product of this reaction, decreases intracellular lipids in vitro by suppressing LXR/SREBP-1c signaling, with regulatory properties opposite to those of its precursor 25-hydroxycholesterol (25HC). Up-regulation of SULT2B1b may be an effective strategy to treat hyperlipidemia and hepatic steatosis. Objectives To explore the effect and mechanism of oxysterol sulfation by SULT2B1b on lipid metabolism in vivo. Methods C57BL/6 and LDLR−/− mice were fed with high-cholesterol diet (HCD) or high-fat diet (HFD) for 10 weeks, and infected with adenovirus encoding SULT2B1b. SULT2B1b expressions in different tissues were determined by immunohistochemistry and western blot. Sulfated oxysterols in liver were analyzed by HPLC. Serum and hepatic lipid levels were determined by Wako Reagents and hematoxylin and eosin (H&E) staining. Gene expressions were determined by real-time RT-PCR and Western Blot. Results Following infection, SULT2B1b was successfully overexpressed in liver, aorta and lung tissues, but not in heart or kidney. SULT2B1b overexpression, combined with administration of 25HC, significantly increased the formation of 25HC3S in liver tissue; significantly decreased serum and hepatic lipid levels, including triglycerides, total cholesterol, free cholesterol, and free fatty acids, as compared to controls both in C57BL/6 and LDLR−/− mice. Gene expression analysis showed that increases in SULT2B1b expression were accompanied by reduction in key regulators and enzymes involved in lipid metabolism, including LXRα, SREBP-1, SREBP-2, acetyl-CoA carboxylase-1 (ACC1) and fatty acid synthase (FAS). Conclusion These findings support the hypothesis that 25HC3S is an important endogenous regulator of lipid biosynthesis. This pathway may represent a novel target for pharmacological intervention in NAFLD. PMID:22225954

  4. THE SPITZER ICE LEGACY: ICE EVOLUTION FROM CORES TO PROTOSTARS

    SciTech Connect

    Oeberg, Karin I.; Boogert, A. C. Adwin; Pontoppidan, Klaus M.; Van den Broek, Saskia; Van Dishoeck, Ewine F.; Bottinelli, Sandrine; Blake, Geoffrey A.; Evans, Neal J.

    2011-10-20

    Ices regulate much of the chemistry during star formation and account for up to 80% of the available oxygen and carbon. In this paper, we use the Spitzer c2d Legacy ice survey, complimented with data sets on ices in cloud cores and high-mass protostars, to determine standard ice abundances and to present a coherent picture of the evolution of ices during low- and high-mass star formation. The median ice composition H{sub 2}O:CO:CO{sub 2}:CH{sub 3}OH:NH{sub 3}:CH{sub 4}:XCN is 100:29:29:3:5:5:0.3 and 100:13:13:4:5:2:0.6 toward low- and high-mass protostars, respectively, and 100:31:38:4:-:-:- in cloud cores. In the low-mass sample, the ice abundances with respect to H{sub 2}O of CH{sub 4}, NH{sub 3}, and the component of CO{sub 2} mixed with H{sub 2}O typically vary by <25%, indicative of co-formation with H{sub 2}O. In contrast, some CO and CO{sub 2} ice components, XCN, and CH{sub 3}OH vary by factors 2-10 between the lower and upper quartile. The XCN band correlates with CO, consistent with its OCN{sup -} identification. The origin(s) of the different levels of ice abundance variations are constrained by comparing ice inventories toward different types of protostars and background stars, through ice mapping, analysis of cloud-to-cloud variations, and ice (anti-)correlations. Based on the analysis, the first ice formation phase is driven by hydrogenation of atoms, which results in an H{sub 2}O-dominated ice. At later prestellar times, CO freezes out and variations in CO freezeout levels and the subsequent CO-based chemistry can explain most of the observed ice abundance variations. The last important ice evolution stage is thermal and UV processing around protostars, resulting in CO desorption, ice segregation, and the formation of complex organic molecules. The distribution of cometary ice abundances is consistent with the idea that most cometary ices have a protostellar origin.

  5. 75 FR 34062 - Airworthiness Directives; Eurocopter France Model AS 350 B, BA, B1, B2, B3, and D, and Model...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-06-16

    ... April 11, 2000 (65 FR 19477-78). Examining the Docket You may examine the docket that contains the...'' under the DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and 3. Will not have... Directives; Eurocopter France Model AS 350 B, BA, B1, B2, B3, and D, and Model AS355 E, F, F1, F2, and...

  6. 20 CFR Appendix B to Part 718 - Standards for Administration and Interpretation of Pulmonary Function Tests. Tables B1, B2, B3...

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 20 Employees' Benefits 4 2014-04-01 2014-04-01 false Standards for Administration and Interpretation of Pulmonary Function Tests. Tables B1, B2, B3, B4, B5, B6. B Appendix B to Part 718 Employees' Benefits OFFICE OF WORKERS' COMPENSATION PROGRAMS, DEPARTMENT OF LABOR FEDERAL COAL MINE HEALTH AND SAFETY ACT OF 1969, AS AMENDED STANDARDS...

  7. Kinematics of powerful jets from intermediate-mass protostars in the Carina nebula

    NASA Astrophysics Data System (ADS)

    Reiter, Megan; Smith, Nathan

    2014-12-01

    We present measurements of proper motions and radial velocities of four powerful Herbig-Haro (HH) jets in the Carina nebula: HH 666, HH 901, HH 902, and HH 1066. Two epochs of Hubble Space Telescope imaging separated by a time baseline of ˜4.4 yr provide proper motions that allow us to measure the transverse velocities of the jets, while ground-based spectra sample their Doppler velocities. Together these yield full three-dimensional space velocities. Aside from HH 666, their identification as outflows was previously inferred only from morphology in images. Proper motions now show decisively that these objects are indeed jets, and confirm that the intermediate-mass protostars identified as the candidate driving sources for HH 666 and HH 1066 are indeed the origin of these outflows. The appearance of two new knots in the HH 1066 jet suggests recent (˜35 yr) changes in the accretion rate, underscoring the variable nature of accretion and outflow in the formation of intermediate-mass stars. In fact, kinematics and mass-ejection histories for all the jets suggest highly episodic mass loss, and point towards pronounced accretion fluctuations. Overall, we measure velocities similar to those found for low-mass protostars. However, the HH jets in Carina have higher densities and are more massive than their low-mass counterparts. Coarse estimates suggest that the heavy jets of intermediate-mass protostars can compete with or even exceed inject ˜10 or more times the cumulative momentum injection of lower mass protostars.

  8. LUMINOSITY FUNCTIONS OF SPITZER-IDENTIFIED PROTOSTARS IN NINE NEARBY MOLECULAR CLOUDS

    SciTech Connect

    Kryukova, E.; Megeath, S. T.; Allen, T. S.; Gutermuth, R. A.; Pipher, J.; Allen, L. E.; Myers, P. C.; Muzerolle, J.

    2012-08-15

    We identify protostars in Spitzer surveys of nine star-forming (SF) molecular clouds within 1 kpc: Serpens, Perseus, Ophiuchus, Chamaeleon, Lupus, Taurus, Orion, Cep OB3, and Mon R2, which combined host over 700 protostar candidates. These clouds encompass a variety of SF environments, including both low-mass and high-mass SF regions, as well as dense clusters and regions of sparsely distributed star formation. Our diverse cloud sample allows us to compare protostar luminosity functions in these varied environments. We combine near- and mid-infrared photometry from the Two Micron All Sky Survey and Spitzer to create 1-24 {mu}m spectral energy distributions (SEDs). Using protostars from the c2d survey with well-determined bolometric luminosities, we derive a relationship between bolometric luminosity, mid-IR luminosity (integrated from 1-24 {mu}m), and SED slope. Estimations of the bolometric luminosities for protostar candidates are combined to create luminosity functions for each cloud. Contamination due to edge-on disks, reddened Class II sources, and galaxies is estimated and removed from the luminosity functions. We find that luminosity functions for high-mass SF clouds (Orion, Mon R2, and Cep OB3) peak near 1 L{sub Sun} and show a tail extending toward luminosities above 100 L{sub Sun }. The luminosity functions of the low-mass SF clouds (Serpens, Perseus, Ophiuchus, Taurus, Lupus, and Chamaeleon) do not exhibit a common peak, however the combined luminosity function of these regions peaks below 1 L{sub Sun }. Finally, we examine the luminosity functions as a function of the local surface density of young stellar objects. In the Orion molecular clouds, we find a significant difference between the luminosity functions of protostars in regions of high and low stellar density, the former of which is biased toward more luminous sources. This may be the result of primordial mass segregation, although this interpretation is not unique. We compare our luminosity

  9. OT2_cceccare_4: Searching for the onset of energetic particle irradiation in Class 0 protostars

    NASA Astrophysics Data System (ADS)

    Ceccarelli, C.

    2011-09-01

    Several evidences tell us that the first stages of low mass star formation are very violent, characterized by, among other phenomena, an intense irradiation of energetic (MeV) particles. The goal of this proposal is to search for signs of MeV particle irradiation in a sample of low to intermediate mass Class 0 protostars. At this end, we propose to observe a selected list of high J HCO+ and N2H+ lines in a selected sample of sources. Based on the observations obtained within the KP CHESS, we estimate a total observing time of 20.5 hours.

  10. Extremely Low Mass: The Circumstellar Envelope of a Potential Proto-Brown Dwarf

    NASA Technical Reports Server (NTRS)

    Wiseman, Jennifer

    2011-01-01

    What is the environment for planet formation around extremely low mass stars? Is the environment around brown dwarfs and extremely low mass stars conducive and sufficiently massive for planet production? The determining conditions may be set very early in the process of the host object's formation. IRAS 16253-2429, the source of the Wasp-Waist Nebula seen in Spitzer IRAC images, is an isolated, very low luminosity ("VeLLO") Class 0 protostar in the nearby rho Ophiuchi cloud. We present VLA ammonia mapping observations of the dense gas envelope feeding the central core accreting system. We find a flattened envelope perpendicular to the outflow axis, and gas cavities that appear to cradle the outflow lobes as though carved out by the flow and associated (apparently precessing) jet, indicating environmental disruption. Based on the NH3 (1,1) and (2,2) emission distribution, we derive the mass, velocity fields and temperature distribution for the envelope. We discuss the combined evidence for this source to be one of the youngest and lowest mass sources in formation yet known, and discuss the ramifications for planet formation potential in this extremely low mass system.

  11. Chemical Changes During Star Formation: High vs. Low-mass YSOs

    NASA Astrophysics Data System (ADS)

    van Dishoeck, Ewine F.

    An overview of recent single-dish surveys of molecular species at infrared and submillimeter wavelengths in a set of high- and low-mass young stellar objects will be presented. The importance of flexible radiative transfer tools for deriving reliable abundances will be emphasized. The temperature and density structures of the envelopes ---an essential ingredient in the analysis--- are constrained from observations of the dust continuum and CS excitation. In high mass objects, clear evidence is seen for abundance jumps of various molecules in the inner warm part of the envelopes. Systematic trends in the abundances and gas/solid ratios with enhanced dust and gas temperatures are found, which may be related to the evolutionary state of the objects. Recent results on combined ISO-SWS, ISO-LWS and SWAS observations of H2O are summarized. The results for high-mass objects will be compared with those for low-mass class 0 and I objects, with special emphasis on the deeply embedded IRAS 16293 -2422 protostar. Geometry appears to play a more important role in the analysis of data for low-mass objects. The observations are interpreted with detailed time-dependent chemical models using the inferred physical structure as input. The importance of freeze-out in the outer envelope as well as ice evaporation and high-temperature reactions in the inner envelope are discussed. See: astro-ph/0205457; astro-ph/0205292; astro-ph/0205068; astro-ph/0201317.

  12. Probing the methanol and CO snow lines in young protostars

    NASA Astrophysics Data System (ADS)

    Anderl, S.; Maret, S.

    2016-05-01

    "Snow lines", marking regions where abundant volatiles freeze out onto the surface of dust grains, play an important role for planet growth and bulk composition in protoplanetary disks. However, they can already be observed in the envelopes of the much younger, low-mass Class 0 protostars that are still in their early phase of heavy accretion. The information on the sublimation regions of different kinds of ices can be used to understand the chemistry of the envelope, its temperature and density structure, and may even hint at the history of the accretion process. As part of the CALYPSO Large Program, we have obtained observations of C18O, N2H+ and CH3OH towards the nearest low-luminosity Class 0 protostars with the IRAM Plateau de Bure interferometer at sub-arcsecond resolution. We observe an anti-correlation of C18O and N2H+ in four of these sources, with N2H+ forming a ring (perturbed by the outflow) around the centrally peaked C18O emission. This reveals the CO snow line in these protostellar envelopes with unprecedented resolution. In addition, we observe compact methanol emission towards three of the sources. We have modeled the emission using a chemical model coupled with a radiative transfer module, using the temperature and density profiles self-consistently determined by Kristensen et al. ([4]). We find that for all four sources the CO snow line appears further inwards than expected from the binding energy of pure CO ices. This may hint at CO being frozen out on H2O surfaces or in mixed ices. Our observations can thereby yield clues on the widely unknown composition of interstellar ices, being the initial seeds of complex organic chemistry.

  13. THE FREQUENCY OF LOW-MASS EXOPLANETS

    SciTech Connect

    O'Toole, S. J.; Jones, H. R. A.; Tinney, C. G.; Bailey, J.; Wittenmyer, R. A.; Butler, R. P.; Marcy, G. W.; Carter, B.

    2009-08-20

    We report first results from the Anglo-Australian Telescope Rocky Planet Search-an intensive, high-precision Doppler planet search targeting low-mass exoplanets in contiguous 48 night observing blocks. On this run, we targeted 24 bright, nearby and intrinsically stable Sun-like stars selected from the Anglo-Australian Planet Search's main sample. These observations have already detected one low-mass planet reported elsewhere (HD 16417b), and here we reconfirm the detection of HD 4308b. Further, we have Monte Carlo simulated data from this run on a star-by-star basis to produce robust detection constraints. These simulations demonstrate clear differences in the exoplanet detectability functions from star to star due to differences in sampling, data quality and intrinsic stellar stability. They reinforce the importance of star-by-star simulation when interpreting the data from Doppler planet searches. These simulations indicate that for some of our target stars we are sensitive to close-orbiting planets as small as a few Earth masses. The two low-mass planets present in our 24-star sample indicate that the exoplanet minimum mass function at low masses is likely to be a flat {alpha} {approx} -1 (for dN/dM {proportional_to} M {sup {alpha}}) and that between 15% {+-} 10% (at {alpha} = -0.3) and 48% {+-} 34% (at {alpha} = -1.3) of stars host planets with orbital periods of less than 16 days and minimum masses greater than 3 M {sub +}.

  14. THIRTY NEW LOW-MASS SPECTROSCOPIC BINARIES

    SciTech Connect

    Shkolnik, Evgenya L.; Hebb, Leslie; Cameron, Andrew C.; Liu, Michael C.; Neill Reid, I. E-mail: Andrew.Cameron@st-and.ac.u E-mail: mliu@ifa.hawaii.ed

    2010-06-20

    As part of our search for young M dwarfs within 25 pc, we acquired high-resolution spectra of 185 low-mass stars compiled by the NStars project that have strong X-ray emission. By cross-correlating these spectra with radial velocity standard stars, we are sensitive to finding multi-lined spectroscopic binaries. We find a low-mass spectroscopic binary fraction of 16% consisting of 27 SB2s, 2 SB3s, and 1 SB4, increasing the number of known low-mass spectroscopic binaries (SBs) by 50% and proving that strong X-ray emission is an extremely efficient way to find M-dwarf SBs. WASP photometry of 23 of these systems revealed two low-mass eclipsing binaries (EBs), bringing the count of known M-dwarf EBs to 15. BD-22 5866, the ESB4, was fully described in 2008 by Shkolnik et al. and CCDM J04404+3127 B consists of two mid-M stars orbiting each other every 2.048 days. WASP also provided rotation periods for 12 systems, and in the cases where the synchronization time scales are short, we used P{sub rot} to determine the true orbital parameters. For those with no P{sub rot}, we used differential radial velocities to set upper limits on orbital periods and semimajor axes. More than half of our sample has near-equal-mass components (q > 0.8). This is expected since our sample is biased toward tight orbits where saturated X-ray emission is due to tidal spin-up rather than stellar youth. Increasing the samples of M-dwarf SBs and EBs is extremely valuable in setting constraints on current theories of stellar multiplicity and evolution scenarios for low-mass multiple systems.

  15. Protostars: Forges of cosmic rays?

    NASA Astrophysics Data System (ADS)

    Padovani, M.; Marcowith, A.; Hennebelle, P.; Ferrière, K.

    2016-05-01

    Context. Galactic cosmic rays are particles presumably accelerated in supernova remnant shocks that propagate in the interstellar medium up to the densest parts of molecular clouds, losing energy and their ionisation efficiency because of the presence of magnetic fields and collisions with molecular hydrogen. Recent observations hint at high levels of ionisation and at the presence of synchrotron emission in protostellar systems, which leads to an apparent contradiction. Aims: We want to explain the origin of these cosmic rays accelerated within young protostars as suggested by observations. Methods: Our modelling consists of a set of conditions that has to be satisfied in order to have an efficient cosmic-ray acceleration through diffusive shock acceleration. We analyse three main acceleration sites (shocks in accretion flows, along the jets, and on protostellar surfaces), then we follow the propagation of these particles through the protostellar system up to the hot spot region. Results: We find that jet shocks can be strong accelerators of cosmic-ray protons, which can be boosted up to relativistic energies. Other promising acceleration sites are protostellar surfaces, where shocks caused by impacting material during the collapse phase are strong enough to accelerate cosmic-ray protons. In contrast, accretion flow shocks are too weak to efficiently accelerate cosmic rays. Though cosmic-ray electrons are weakly accelerated, they can gain a strong boost to relativistic energies through re-acceleration in successive shocks. Conclusions: We suggest a mechanism able to accelerate both cosmic-ray protons and electrons through the diffusive shock acceleration mechanism, which can be used to explain the high ionisation rate and the synchrotron emission observed towards protostellar sources. The existence of an internal source of energetic particles can have a strong and unforeseen impact on the ionisation of the protostellar disc, on the star and planet formation

  16. Discovery of low mass objects in Taurus

    NASA Technical Reports Server (NTRS)

    Forrest, W. J.; Ninkov, Z.; Garnett, J. D.; Skrutskie, M. F.; Shure, M.

    1989-01-01

    In infrared (2.2 micron, K-band) search of small regions (25 in square) near 26 members of the Taurus star-forming association has revealed 20 dim (K = 13-16 mag) stellar objects near 13 of them. Of these 20 objects, 9 are exceptionally red. It is argued that these 9 are probably also Taurus members. From the luminosities (0.4 to 4 times 10 the -3 power luminosity) and ages (estimated at 10(exp 6) years), masses can be determined by reference to theoretical low-mass cooling curves. The masses are in the range 0.005 to 0.015 solar mass, i.e., low-mass brown dwarfs. Proper motion studies of 7 of the objects visible on the POSS plates conducted by Burton Jones establish that 4 are highly probable Taurus members while 1 is a possible member.

  17. Modeling the Submillimeter Dust Continuum Emission from Nearby Low Mass Star Forming Cores

    NASA Astrophysics Data System (ADS)

    Shirley, Y. L.; Young, C. H.; Evans, N. J., II; Rawlings, J. M. C.

    2001-12-01

    Current theories of a low mass star formation predict the evolution of the density distribution, n({r}, t), temperature distribution, T({r}, t), and the velocity field ,{v}({r}, t), of the envelope of protostellar cores with time. Optically thin dust emission at submillimeter wavelengths provides a powerful diagnostic to constrain the envelope density and temperature structure. In this study, thirty-nine low mass cores were mapped with SCUBA at 850 and 450 μ m on the JCMT during sixteen nights between January 1998 and February 2000. The sources were selected from the earliest phases (pre-T Tauri) in the proposed evolutionary scheme for low mass protostars (6 Pre-protostellar Cores (PPCs), 15 Class 0, 18 Class I) with luminosities indicative of low mass star formation (Lbol < 50 Lsun) and with distances less than 450 pc. High signal-to-noise maps allowed azimuthally averaged radial profiling out to 60 arcseconds from the continuum centroid. The similarities and differences in the submillimeter continuum emission properties of the envelopes of PPCs, Class 0, and Class I sources on 103 to 104 AU scales are summarized. We have modeled the normalized radial intensity distributions and spectral energy distributions (SED) for sixteen sources from the SCUBA survey (3 PPCs, 7 Class 0, and 6 Class I) using a one dimensional radiative transfer code (Egan, Leung, & Spagna 1988) with internal heating from a central protostar (Class 0 and I objects) and external heating from the interstellar radiation field (all objects) to calculate the dust temperature distribution. Power law, Bonnor-Ebert, Shu inside-out collapse, and Plummer density distributions were tested to match the observed normalized radial profiles and observed SED simultaneously. Realistic beam profiles and chopping were used to simulate the observations. We find Bonnor-Ebert spheres with central densities of 105 to 106 cm-3 reproduce the PPC radial profiles while power law models (n(r) ~ r-p, p = 1.1 - 2

  18. Calorimetry of low mass Pu239 items

    SciTech Connect

    Cremers, Teresa L; Sampson, Thomas E

    2010-01-01

    Calorimetric assay has the reputation of providing the highest precision and accuracy of all nondestructive assay measurements. Unfortunately, non-destructive assay practitioners and measurement consumers often extend, inappropriately, the high precision and accuracy of calorimetric assay to very low mass items. One purpose of this document is to present more realistic expectations for the random uncertainties associated with calorimetric assay for weapons grade plutonium items with masses of 200 grams or less.

  19. VizieR Online Data Catalog: 6.7GHz methanol masers survey of low-mass YSO (Minier+, 2003)

    NASA Astrophysics Data System (ADS)

    Minier, V.; Ellingsen, S. P.; Norris, R. P.; Booth, R. S.

    2003-07-01

    We report the results of a search for 6.7-GHz methanol masers toward low-mass young stellar objects (YSOs) and (pre)protostellar condensations with the Australia Telescope Compact Array (ATCA). Our sample consisted of 13 class 0 protostars and 44 class I YSOs as well as 66 (pre)protostellar condensations. A single detection was obtained toward NGC 2024: FIR4 in the Orion B region. This is the first detection of a 6.7-GHz methanol maser in Orion. The nature of FIR4 has been a subject of debate with some evidence suggesting that it is a very cold high-mass (pre)protostellar condensation and others arguing that it is a low-mass YSO. The discovery of a methanol maser associated with this source is inconsistent with both of these hypotheses and we suggest that FIR4 probably harbours an intermediate- or high-mass YSO. (1 data file).

  20. Proceedings of Protostars and Planets V

    NASA Technical Reports Server (NTRS)

    2005-01-01

    Oral presentation sessions in this conference include: Clouds and cores; Star formation and protostars; Binaries and multiples; Newborn massive stars; jets and outflows; Clusters and associations; T Tauri stars and disks; Brown dwarfs; Planet formation and evolution; Extrasolar planets; Dust and protoplanetary disks; Early solar system and Astrobiology. Poster presentations included: Clouds and Cores. Collapse and Protostars, Binaries and Multiples, Clusters, Associations, and the IMF, Jets and Outflows, T Tauri Stars and Other Young Stars, Disks and Disk Accretion, Brown Dwarfs, Herbig Ae/Be Stars and Massive Stars, Solar System Objects, Planet Formation, Extrasolar Planets and Planet Detection, Properties of Protoplanetary Disks, Migration and Planetary Orbits and Meteoritics and Astrobiology

  1. Thirty New Low-mass Spectroscopic Binaries

    NASA Astrophysics Data System (ADS)

    Shkolnik, Evgenya L.; Hebb, Leslie; Liu, Michael C.; Reid, I. Neill; Collier Cameron, Andrew

    2010-06-01

    As part of our search for young M dwarfs within 25 pc, we acquired high-resolution spectra of 185 low-mass stars compiled by the NStars project that have strong X-ray emission. By cross-correlating these spectra with radial velocity standard stars, we are sensitive to finding multi-lined spectroscopic binaries. We find a low-mass spectroscopic binary fraction of 16% consisting of 27 SB2s, 2 SB3s, and 1 SB4, increasing the number of known low-mass spectroscopic binaries (SBs) by 50% and proving that strong X-ray emission is an extremely efficient way to find M-dwarf SBs. WASP photometry of 23 of these systems revealed two low-mass eclipsing binaries (EBs), bringing the count of known M-dwarf EBs to 15. BD-22 5866, the ESB4, was fully described in 2008 by Shkolnik et al. and CCDM J04404+3127 B consists of two mid-M stars orbiting each other every 2.048 days. WASP also provided rotation periods for 12 systems, and in the cases where the synchronization time scales are short, we used P rot to determine the true orbital parameters. For those with no P rot, we used differential radial velocities to set upper limits on orbital periods and semimajor axes. More than half of our sample has near-equal-mass components (q > 0.8). This is expected since our sample is biased toward tight orbits where saturated X-ray emission is due to tidal spin-up rather than stellar youth. Increasing the samples of M-dwarf SBs and EBs is extremely valuable in setting constraints on current theories of stellar multiplicity and evolution scenarios for low-mass multiple systems. Based on observations collected at the W. M. Keck Observatory, the Canada-France-Hawaii Telescope and by the WASP Consortium. The Keck Observatory is operated as a scientific partnership between the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W. M. Keck Foundation. The CFHT is operated by the National Research Council of Canada

  2. Spectroscopic Detection of a Stellar-like Photosphere in an Accreting Protostar

    NASA Technical Reports Server (NTRS)

    Greene, Thomas P.; Lada, Charles J.; DeVincenzi, Donald L. (Technical Monitor)

    2002-01-01

    veiling is r(sub k) is greater than or equal to 4.6. Its low luminosity (2 solar masses) and high veiling dictate that its central protostar is very low mass, M is approx. 0.1 solar masses. We also evaluate multi-epoch X ray data along with these spectra and conclude that the X ray variabilities of these sources are not directly related to their protostellar rotation velocities.

  3. OBSERVING SIMULATED PROTOSTARS WITH OUTFLOWS: HOW ACCURATE ARE PROTOSTELLAR PROPERTIES INFERRED FROM SEDs?

    SciTech Connect

    Offner, Stella S. R.; Robitaille, Thomas P.; Hansen, Charles E.; Klein, Richard I.; McKee, Christopher F.

    2012-07-10

    The properties of unresolved protostars and their local environment are frequently inferred from spectral energy distributions (SEDs) using radiative transfer modeling. In this paper, we use synthetic observations of realistic star formation simulations to evaluate the accuracy of properties inferred from fitting model SEDs to observations. We use ORION, an adaptive mesh refinement (AMR) three-dimensional gravito-radiation-hydrodynamics code, to simulate low-mass star formation in a turbulent molecular cloud including the effects of protostellar outflows. To obtain the dust temperature distribution and SEDs of the forming protostars, we post-process the simulations using HYPERION, a state-of-the-art Monte Carlo radiative transfer code. We find that the ORION and HYPERION dust temperatures typically agree within a factor of two. We compare synthetic SEDs of embedded protostars for a range of evolutionary times, simulation resolutions, aperture sizes, and viewing angles. We demonstrate that complex, asymmetric gas morphology leads to a variety of classifications for individual objects as a function of viewing angle. We derive best-fit source parameters for each SED through comparison with a pre-computed grid of radiative transfer models. While the SED models correctly identify the evolutionary stage of the synthetic sources as embedded protostars, we show that the disk and stellar parameters can be very discrepant from the simulated values, which is expected since the disk and central source are obscured by the protostellar envelope. Parameters such as the stellar accretion rate, stellar mass, and disk mass show better agreement, but can still deviate significantly, and the agreement may in some cases be artificially good due to the limited range of parameters in the set of model SEDs. Lack of correlation between the model and simulation properties in many individual instances cautions against overinterpreting properties inferred from SEDs for unresolved protostellar

  4. Simultaneous determination of vitamins B1, B2, B6, and niacinamide in multivitamin pharmaceutical preparations by paired-ion reversed-phase high-pressure liquid chromatography.

    PubMed

    Kwok, R P; Rose, W P; Tabor, R; Pattison, T S

    1981-09-01

    A high-pressure liquid chromatographic procedure for the simultaneous determination of vitamins B1, B2, B6, and niacinamide in multivitamin pharmaceutical preparations was developed and evaluated. The method uses paired-ion reversed-phase partition chromatography for baseline separation of the four water-soluble vitamins. This method was applied to the analysis of a multivitamin and multivitamin-multimineral tablets, and a technique was developed to reduce vitamin adsorption by the minerals. The results obtained by this method were compared with those obtained by the official methods. It was concluded that this method is fast, accurate, specific, and suitable for routine quality control use. PMID:6101144

  5. ASSESSMENT OF INTAKE AND NUTRITIONAL STATUS OF VITAMIN B1, B2, AND B6 IN MEN AND WOMEN WITH DIFFERENT PHYSICAL ACTIVITY LEVELS

    PubMed Central

    Hübner-Wozniak, E.; Lewandowska, I.

    2013-01-01

    The purpose of the present study was to examine the nutritional status of vitamin B1, B2, and B6 in respect to dietary intake of these vitamins and activity coefficients of the erythrocyte enzymes transketolase, glutathione reductase, and aspartic aminotransferase in young men and women with different physical activity levels. The participants of this study were 20 women and 20 men with high physical activity (groups HAW and HAM, respectively), and 20 women and 20 men with low physical activity (groups LAW and LAM, respectively). The intake of vitamins B1, B2, B6, proteins, and calorie content of the diet was based on the average of the 4-day dietary recalls. To assess nutritional status of vitamin B1, B2, and B6, the activity coefficients (α) of erythrocyte transketolase (ETK), erythrocyte glutathione reductase (EGR), and erythrocyte aspartic aminotransferase (EAST) were estimated in blood hemolysates. The intake of the studied vitamins in the diet was statistically significantly lower in the female groups compared with the respective male groups. Deficiency of vitamin B6 in the diet was present more often in women than in men (in terms of the recommended dietary allowances [RDA]). Values of the activity coefficient αETK indicated that none of the groups in this study suffered the risk of vitamin B1 deficiency. The value of the activity coefficient αEGR indicated that the groups of women and men with low physical activity were more prone to vitamin B2 deficiency compared with the high physical activity groups. The risk of vitamin B6 deficiency (αEAST) in both male groups was higher than in both female groups. The obtained results do not allow for unequivocal determination of the impact of sex and the level of physical activity on intake and nutritional status of vitamin B1, B2, and B6. Independently of sex and the level of physical activity, the women and men consumed insufficient quantities of vitamins B1 and B6, although this was not always related to

  6. Protostars at Low Extinction in Orion A

    NASA Astrophysics Data System (ADS)

    Lewis, John Arban; Lada, Charles J.

    2016-07-01

    In the list of young stellar objects (YSOs) compiled by Megeath et al. for the Orion A molecular cloud, only 44 out of 1208 sources found projected onto low extinction ({A}{{K}}\\lt 0.8 mag) gas are identified as protostars. These objects are puzzling because protostars are not typically expected to be associated with extended low extinction material. Here, we use high resolution extinction maps generated from Herschel data, optical/infrared and Spitzer Space Telescope photometry and spectroscopy of the low extinction protostellar candidate sources to determine if they are likely true protostellar sources or contaminants. Out of 44 candidate objects, we determine that 10 sources are likely protostars, with the rest being more evolved YSOs (18), galaxies (4), false detections of nebulosity and cloud edges (9), or real sources for which more data are required to ascertain their nature (3). We find none of the confirmed protostars to be associated with recognizable dense cores and we briefly discuss possible origins for these orphaned objects.

  7. Spectroscopic Observations of Nearby Low Mass Stars

    NASA Astrophysics Data System (ADS)

    Vican, Laura; Zuckerman, B. M.; Rodriguez, D.

    2014-01-01

    Young low-mass stars are known to be bright in X-ray and UV due to a high level of magnetic activity. By cross-correlating the GALEX Catalog with the WISE and 2MASS Point Source Catalogs, we have identified more than 2,000 stars whose UV excesses suggest ages in the 10-100 Myr range. We used the Shane 3-m telescope at Lick Observatory on Mount Hamilton, California to observe some of these 2,000 stars spectroscopically. We measured the equivalent width of lithium at 6708 A absorption and H-alpha emission lines. Out of a total of 122 stars observed with the Kast grating spectrometer, we find that roughly 10% have strong lithium absorption features. The high percentage of stars with lithium present is further evidence of the importance of UV emission as a youth indicator for low-mass stars. In addition, we used high-resolution spectra obtained with the Hamilton echelle spectrograph to determine radial velocities for several UV-bright stars. These radial velocities will be useful for the calculation of Galactic UVW space velocities for determination of possible moving group membership. This work is supported by NASA Astrophysics Data Analysis Program award NNX12AH37G to RIT and UCLA and Chilean FONDECYT grant 3130520 to Universidad de Chile. This submission presents work for the GALNYSS project and should be linked to abstracts submitted by David Rodriguez, Laura Vican, and Joel Kastner.

  8. Wave-of-Advance Models of the Diffusion of the Y Chromosome Haplogroup R1b1b2 in Europe

    PubMed Central

    Sjödin, Per; François, Olivier

    2011-01-01

    Whether or not the spread of agriculture in Europe was accompanied by movements of people is a long-standing question in archeology and anthropology, which has been frequently addressed with the help of population genetic data. Estimates on dates of expansion and geographic origins obtained from genetic data are however sensitive to the calibration of mutation rates and to the mathematical models used to perform inference. For instance, recent data on the Y chromosome haplogroup R1b1b2 (M269) have either suggested a Neolithic origin for European paternal lineages or a more ancient Paleolithic origin depending on the calibration of Y-STR mutation rates. Here we examine the date of expansion and the geographic origin of hgR1b1b2 considering two current estimates of mutation rates in a total of fourteen realistic wave-of-advance models. We report that a range expansion dating to the Paleolithic is unlikely to explain the observed geographical distribution of microsatellite diversity, and that whether the data is informative with respect to the spread of agriculture in Europe depends on the mutation rate assumption in a critical way. PMID:21720564

  9. Subtyping of Y-chromosomal haplogroup E-M78 (E1b1b1a) by SNP assay and its forensic application.

    PubMed

    Caratti, S; Gino, S; Torre, C; Robino, C

    2009-07-01

    The continual discovery of new single-nucleotide polymorphisms (SNPs) has led to an increased resolution of the Y chromosome phylogeny. Some of these Y-SNPs have shown to be restricted to small geographical regions and therefore may prove useful in the forensic field as tools for the prediction of population of origin of unknown casework samples. Here, we describe a system for the molecular dissection of haplogroup E-M78 (E1b1b1a), consisting of multiplex polymerase chain reaction and minisequencing of M78 and nine population-informative Y-SNPs (M148, M224, V12, V13, V19, V22, V27, V32, V65) in a single reaction. Sensitivity and admixture studies demonstrated that the SNP protocol allows robust genotyping from as little as 50 pg of male DNA, even in the presence of 500-fold amounts of female DNA. In order to evaluate the suitability of E1b1b1a, subhaplogrouping for population-of-origin prediction, the distribution of E-M78 and its derived variants was determined in an Italian population sample (n = 326). PMID:19430804

  10. Low-Mass Star Formation and the Initial Mass Function in Young Clusters

    NASA Astrophysics Data System (ADS)

    Luhman, Kevin Lee

    I have used optical and near-infrared spectroscopy and imaging to measure spectral types and luminosities for young (/tau<10 Myr), embedded (AV=0[-]50), low-mass (0.1-1 Msolar) stars in three nearby (d<300 pc) clusters: L1495E, IC 348, and ρ Ophiuchi. In conjunction with theoretical evolutionary tracks, I have derived the star formation history and initial mass function for each stellar population. A large number of brown dwarf candidates have been identified in the photometry, several of which are confirmed through spectroscopy. Finally, I have measured the frequency and survival times of circumstellar disks and investigated the photometric and spectroscopic properties of protostars. In S 2, I apply observational tests to the available sets of evolutionary models for low-mass stars, concluding that the calculations of D'Antona & Mazzitelli are preferred for the range of masses and ages considered here. In S 3 and S 4, I examine in detail the spectroscopic characteristics and substellar nature of two brown dwarf candidates. The study then expands to include the populations within the clusters L1495E (S 5), IC 348 (S 6), and ρ Ophiuchi (S 7). In S 8, I briefly discuss the past, present, and future of scientific research related to this thesis.

  11. Olivier Chesneau's Work on Low Mass Stars

    NASA Astrophysics Data System (ADS)

    Lagadec, E.

    2015-12-01

    During his too short career, Olivier Chesneau pioneered the study of the circumstellar environments of low mass evolved stars using very high angular resolution techniques. He applied state of the art high angular resolution techniques, such as optical interferometry and adaptive optics imaging, to the the study of a variety of objects, from AGB stars to Planetary Nebulae, via e.g. Born Again stars, RCB stars and Novae. I present here an overview of this work and most important results by focusing on the paths he followed and key encounters he made to reach these results. Olivier liked to work in teams and was very strong at linking people with complementary expertises to whom he would communicate his enthusiasm and sharp ideas. His legacy will live on through the many people he inspired.

  12. SP-100 low mass shield design

    NASA Astrophysics Data System (ADS)

    Carlson, D. E.

    1985-09-01

    The shielding considerations for an unmanned space reactor system are somewhat different from those for a terrestrial reactor. An unmanned operation in space implies that only a shadow shield, rather than a 4(PI) one, is required to protect payload hardware that typically can tolerate 10(4) to 10(6) times more radiation than can a human crew. On the other hand, the system mass, of which the radiation shield can be a significant fraction, is a severe constraint for space reactors and not normally a problem with terrestrial ones. The object of this paper is to briefly summarize advancements made on various aspects of low mass shield design for space reactors, including materials and their arrangements, geometric factors and their potential impact on system design optimization, and proposed new configuration concepts for further mass reduction.

  13. Pseudocepheids. III - The low-mass stars

    NASA Astrophysics Data System (ADS)

    Eggen, O. J.

    1986-04-01

    Light and color curves in four-color, H-beta, and (RI) photometric systems are presented for 20 low-mass pseudocepheids. Members of the Wolf 630 group and the cluster M67 are used to establish the positions of both variable and nonvariable giants with near solar abundance in the luminosity-temperature plane for old disk population stars, while members of Omega Cen and of Kapteyn's Star Group are used for the low metal abundance halo giants. The low-mass pseudocepheids discussed are divided into two main categories, based on the amplitude of light variation. The smaller amplitude stars, characterized by R CrB and RY Sgr in the old disk population, show the R CrB syndrome of occasional deep light minima, as does UW Cen. The small amplitude variables in the halo population, BL Tel and LN Hya, do not show the R CrB syndrome and their periods are longer than those of old disk stars. Large amplitude variables, with periods ranging from 10 to 150 days, are all halo objects with stability of period and form of light curve an obvious function of the period. Cen and BL Tel are members of Kapteyn's Star Group, and the spectroscopic orbital elements of the latter indicate a mass near 0.5 solar mass for the pseudocepheid and 1 solar mass for the late-type giant companion. Far-infrared observations are important in exploring the correlations between the presence and character of circumstellar dust shells and other post-AGB star parameters.

  14. Current Advances in the Computational Simulation of the Formation of Low-Mass Stars

    SciTech Connect

    Klein, R I; Inutsuka, S; Padoan, P; Tomisaka, K

    2005-10-24

    Developing a theory of low-mass star formation ({approx} 0.1 to 3 M{sub {circle_dot}}) remains one of the most elusive and important goals of theoretical astrophysics. The star-formation process is the outcome of the complex dynamics of interstellar gas involving non-linear interactions of turbulence, gravity, magnetic field and radiation. The evolution of protostellar condensations, from the moment they are assembled by turbulent flows to the time they reach stellar densities, spans an enormous range of scales, resulting in a major computational challenge for simulations. Since the previous Protostars and Planets conference, dramatic advances in the development of new numerical algorithmic techniques have been successfully implemented on large scale parallel supercomputers. Among such techniques, Adaptive Mesh Refinement and Smooth Particle Hydrodynamics have provided frameworks to simulate the process of low-mass star formation with a very large dynamic range. It is now feasible to explore the turbulent fragmentation of molecular clouds and the gravitational collapse of cores into stars self-consistently within the same calculation. The increased sophistication of these powerful methods comes with substantial caveats associated with the use of the techniques and the interpretation of the numerical results. In this review, we examine what has been accomplished in the field and present a critique of both numerical methods and scientific results. We stress that computational simulations should obey the available observational constraints and demonstrate numerical convergence. Failing this, results of large scale simulations do not advance our understanding of low-mass star formation.

  15. Protostar formation in the early universe.

    PubMed

    Yoshida, Naoki; Omukai, Kazuyuki; Hernquist, Lars

    2008-08-01

    The nature of the first generation of stars in the universe remains largely unknown. Observations imply the existence of massive primordial stars early in the history of the universe, and the standard theory for the growth of cosmic structure predicts that structures grow hierarchically through gravitational instability. We have developed an ab initio computer simulation of the formation of primordial stars that follows the relevant atomic and molecular processes in a primordial gas in an expanding universe. The results show that primeval density fluctuations left over from the Big Bang can drive the formation of a tiny protostar with a mass 1% that of the Sun. The protostar is a seed for the subsequent formation of a massive primordial star. PMID:18669856

  16. Vavilosides A1/A2-B1/B2, new furostane glycosides from the bulbs of Allium vavilovii with cytotoxic activity.

    PubMed

    Zolfaghari, Behzad; Sadeghi, Masoud; Troiano, Raffaele; Lanzotti, Virginia

    2013-04-01

    A phytochemical analysis of the bulbs of Allium vavilovii M. Pop. & Vved. was attained for the first time extensively, affording to the isolation of four new furostanol saponins, named vavilosides A1/A2-B1/B2 (1a/b-2a/2b), as two couple of isomers in equilibrium, together with ascalonicoside A1/A2 (3a/3b) and 22-O-methyl ascalonicoside A1/A2 (4a/4b), previously isolated from shallot, Allium ascalonicum. High concentrations of kaempferol, kaempferide, and kaempferol 4(I)-glucoside were also isolated. The chemical structures of the new compounds, established through a combination of extensive nuclear magnetic resonance, mass spectrometry and chemical analyses, were identified as (25R)-furost-5(6)-en-1β,3β,22α,26-tetraol 1-O-α-L-rhamnopyranosyl-(1→2)-O-β-D-galactopyranosyl 26-O-α-L-rhamnopyranoside (vaviloside A1), (25R)-furost-5(6)-en-1β,3β,22β,26-tetraol 1-O-α-L-rhamnopyranosyl-(1→2)-O-β-D-galactopyranosyl 26-O-α-L-rhamnopyranoside (vaviloside A2), (25R)-furost-5(6)-en-1β,3β,22α,26-tetraol 1-O-α-L-rhamnopyranosyl-(1→2)-O-β-D-xylopyranosyl 26-O-α-L-rhamnopyranoside (vaviloside B1), (25R)-furost-5(6)-en-1β,3β,22β,26-tetraol 1-O-α-L-rhamnopyranosyl-(1→2)-O-β-d-xylopyranosyl 26-O-α-L-rhamnopyranoside (vaviloside B2). The isolated saponins showed cytotoxic activity on J-774, murine monocyte/macrophage, and WEHI-164, murine fibrosarcoma, cell lines with the following rank: vaviloside B1/B2>ascalonicoside A1/A2>vaviloside A1/A2. PMID:23415085

  17. Evolutionary models of rotating low mass stars

    NASA Astrophysics Data System (ADS)

    Mendes, Luiz Themystokliz Sanctos

    1999-11-01

    We have investigated the combined effects of rotation and internal angular momentum redistribution on the structure and evolution of low mass stars, from the pre-main sequence to the main sequence phase. As a tool for that study, the ATON stellar evolutionary code (Mazzitelli 1989; Ventura et al. 1998) has been modified in order to include those effects. Rotation was implemented according to the equipotential technique developed by Kippenhahn & Thomas (1970) and later improved by Endal & Sofia (1976). Angular momentum redistribution in radiative regions was modeled through an advection-diffusion partial differential equation based on the framework originally introduced by Chaboyer & Zahn (1992), which is based on the sole assumption of stronger turbulent transport in the horizontal direction than in the vertical one. The diffusion coefficient of this equation is obtained from characteristic lengths and velocities of typical rotation-induced hydrodynamical instabilities. This improved code was used to compute a series of rotating low mass stellar models (with masses ranging from 1.2Modot down to 0.6 Modot). Regarding the structural (hydrostatic) effects of rotation, the general features of these models show that rotating stars behave as if they were non-rotating stars of slightly lower masses, in accordance with previous results by other researchers. A study of this mass-lowering effect for the considered range of masses shows that rotation decreases lithium depletion while the star is fully convective but increases it as soon as the star develops a radiative core. The net effect is a enhanced lithium depletion, in disagreement with observational data which suggest that faster rotators in young open clusters experience less lithium depletion. Angular momentum redistribution in the considered models is very effective in smoothing their internal angular velocity profile as soon as the star reaches the zero age main sequence, but fails to reproduce the flat solar

  18. 30 Doradus: The Low-Mass Stars

    NASA Astrophysics Data System (ADS)

    Zinnecker, H.; Brandl, B.; Brandner, W.; Moneti, A.; Hunter, D.

    We have obtained HST/NICMOS H-band images of the central 1'x1' field around the R136 starburst cluster in the 30 Doradus HII region, in an attempt to reveal the presence (or absence) of a low-mass stellar population (M < 1 Mo). We will discuss the fascinating prospect of 30 Dor/R136 being a proto-globular cluster and a template starburst unit. At the time of writing, we are still working to determine which method and photometry package is best suited to our 0.15" NICMOS images, which are characterised by extreme crowding in the cluster center and a peculiar and slightly undersampled NICMOS PSF. The main difficulty with the PSF is identifying the many "dots" that appear outside the Airy ring as PSF features and not as faint stars. Prelimininary analysis suggests that the H-band luminosity function rises at least until H = 20 (2 Mo). We have detected numerous stars with 20.0 < H < 22.5 (the latter corresponding to 0.4 Mo) beyond about 7" from the cluster centre, but we have not yet determined the completeness in that magnitude range, and we are not yet in a position to make a statement about the shape of the H-band luminosity function there. We have combined our infrared data with the optical WFPC2 images of Hunter et al. (1995) to produce a VIH 3-colour image of the central 30" x 30" area. The result clearly shows unexpected patches of extinction, with one patch only about 5" from the cluster core.

  19. Microwave Spectroscopy of Complex Molecules Around the Young Protostar Chamaeleon MMS1

    NASA Technical Reports Server (NTRS)

    Cordiner, Martin A.; Charnley, Steven B.; Wirstrom, Eva S.; Smith, Robert G.

    2011-01-01

    Observations are presented of emission lines from organic molecules at frequencies 30-100 GHz in the vicinity of the extremely young, chemically rich, very low-luminosity protostar and candidate first hydrostatic core Chamaeleon MMS1. Column densities are derived and emission maps are presented for species including polyynes, cyanopolyynes, sulphuretted carbon-chains and methanol. Emission from the carbon-chain-bearing species peaks very near to the protostar; methanol peaks about 0.1 pc further away. The mean molecular hydrogen number density is calculated to be 10(exp 6) per cc. and the gas kinetic temperature is in the range 4-7 K. The abundances of long carbon chains (including C6H and HC7N) are very large -- similar to those found in the most carbon-chain-rich regions of the Galaxy, and indicative of a non-equilibrium carbon chemistry. The observed methanol and acetaldehyde abundances indicate active grain-surface chemistry and desorption processes. The carbon-chain anions C4H- and C6H- were not detected and the upper limit on the anion-to-neutral ratio for C4H- is less than 0.02% and for C6H-, less than 10%. These values are consistent with previous observations in interstellar clouds and low-mass protostars. Deuterated HC3N and c-C3H2 were detected, with fractionation ratios of about 4%, and 22%, respectively. A low c-C3H2 ortho-to-para ratio was measured, which is consistent with a molecular hydrogen ortho-to-para ratio of close to zero and implies a relatively young chemical age (less than about 10(exp 5) yr) for the matter surrounding Cha-MMS1. These observations show that a high level of chemical complexity can be present in star-forming gas.

  20. Detection of glycolaldehyde toward the solar-type protostar NGC 1333 IRAS2A

    NASA Astrophysics Data System (ADS)

    Coutens, A.; Persson, M. V.; Jørgensen, J. K.; Wampfler, S. F.; Lykke, J. M.

    2015-04-01

    Glycolaldehyde is a key molecule in the formation of biologically relevant molecules such as ribose. We report its detection with the Plateau de Bure interferometer toward the Class 0 young stellar object NGC 1333 IRAS2A, which is only the second solar-type protostar for which this prebiotic molecule is detected. Local thermodynamic equilibrium analyses of glycolaldehyde, ethylene glycol (the reduced alcohol of glycolaldehyde), and methyl formate (the most abundant isomer of glycolaldehyde) were carried out. The relative abundance of ethylene glycol to glycolaldehyde is found to be ~5 - higher than in the Class 0 source IRAS 16293-2422 (~1), but similar to the lower limits derived in comets (≥3-6). The different ethylene glycol-to-glycolaldehyde ratios in the two protostars might be related to different CH3OH:CO compositions of the icy grain mantles. In particular, a more efficient hydrogenation on the grains in NGC 1333 IRAS2A would favor the formation of both methanol and ethylene glycol. In conclusion, it is possible that like NGC 1333 IRAS2A, other low-mass protostars show high ethylene glycol-to-glycolaldehyde abundance ratios. The cometary ratios might consequently be inherited from earlier stages of star formation if the young Sun experienced conditions similar to NGC 1333 IRAS2A. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).Figures 3-4 and Table 1 are available in electronic form at http://www.aanda.org

  1. Organic Chemistry of Low-Mass Star-Forming Cores. I. 7 mm Spectroscopy of Chamaeleon MMSl

    NASA Technical Reports Server (NTRS)

    Cordiner, Martn A.; Charnley, Steven B.; Wirtstroem, Eva S.; Smith, Robert G.

    2012-01-01

    Observations are presented of emission lines from organic molecules at frequencies 32-50 GHz in the vicinity of Chamaeleon MMS1. This chemically rich dense cloud core harbors an extremely young, very low luminosity protostellar object and is a candidate first hydrostatic core. Column densities are derived and emission maps are presented for species including polyynes, cyanopolyynes, sulphuretted carbon chains, and methanol. The polyyne emission peak lies about 5000 AU from the protostar, whereas methanol peaks about 15,000 AU away. Averaged over the telescope beam, the molecular hydrogen number density is calculated to be 10(exp 6) / cubic cm and the gas kinetic temperature is in the range 5-7 K. The abundances of long carbon chains are very large and are indicative of a nonequilibrium carbon chemistry; C6H and HC7N column densities are 5.9(sup +2.9) (sub -1.3) x 10(exp 11) /cubic cm and 3.3 (sup +8.0)(sub -1.5) x 10(exp 12)/sq cm, respectively, which are similar to the values found in the most carbon-chain-rich protostars and prestellar cores known, and are unusually large for star-forming gas. Column density upper limits were obtained for the carbon chain anions C4H(-) and C6H(-), with anion-to-neutral ratios [C4H(-)]/[C4H] < 0.02% and [C6H(-l)]/[C6H] < 10%, consistent with previous observations in interstellar clouds and low-mass protostars. Deuterated HC,3 and c-C3H2 were detected. The [DC3N]/[HC,N] ratio of approximately 4% is consistent with the value typically found in cold interstellar gas.

  2. The formation of a massive protostar through the disk accretion of gas.

    PubMed

    Chini, Rolf; Hoffmeister, Vera; Kimeswenger, Stefan; Nielbock, Markus; Nürnberger, Dieter; Schmidtobreick, Linda; Sterzik, Michael

    2004-05-13

    The formation of low-mass stars like our Sun can be explained by the gravitational collapse of a molecular cloud fragment into a protostellar core and the subsequent accretion of gas and dust from the surrounding interstellar medium. Theoretical considerations suggest that the radiation pressure from the protostar on the in-falling material may prevent the formation of stars above ten solar masses through this mechanism, although some calculations have claimed that stars up to 40 solar masses can in principle be formed via accretion through a disk. Given this uncertainty and the fact that most massive stars are born in dense clusters, it was suggested that high-mass stars are the result of the runaway merging of intermediate-mass stars. Here we report observations that clearly show a massive star being born from a large rotating accretion disk. The protostar has already assembled about 20 solar masses, and the accretion process is still going on. The gas reservoir of the circumstellar disk contains at least 100 solar masses of additional gas, providing sufficient fuel for substantial further growth of the forming star. PMID:15141204

  3. Habitable Zones Around Low-Mass Stars

    NASA Astrophysics Data System (ADS)

    Kopparapu, Ravi Kumar; Kasting, J. F.; Ramirez, R.

    2011-09-01

    Classically, the circumstellar habitable zone (HZ) is defined as the region inside which a terrestrial mass planet, with adequate supplies of carbon, water, and internal heat, can sustain liquid water on its surface (Kasting et al. 1993). A conservative estimate for the width of the HZ in our Solar system is 0.93-1.48 AU, assuming that the inner edge is limited by water loss and the outer edge is determined by the maximum greenhouse limit for a dense CO2 atmosphere. These numbers are revisions of ones published by Kasting et al. (1993), based on new climate modeling results. Kasting et al. obtained HZ boundaries for stars with effective temperatures between 3700 K and 7200 K--limits that do not include main-sequence M-dwarfs. In this study we use an updated 1-D radiative-convective, cloud-free climate model to estimate the width of the HZ around these low mass stars. Significant improvements in our climate model include: (1) updated collision-induced absorption coefficients for CO2 (critical for dense CO2 atmospheres at the outer edge) and (2) a revised Rayleigh scattering coefficient for H2O (important for water loss at the inner edge). Assuming Earth-like planets with CO2/H2O/N2 atmospheres, the width of the HZ is 0.24-0.44 AU around an early M star (Teff = 3600 K) and 0.05-0.09 AU for a late M star (Teff = 2800 K). As our model does not include the radiative effects of clouds, the actual HZ boundaries may extend further in both directions than our conservative estimates. Nonetheless, current ground-based surveys (e.g., the MEARTH project) and future space-based characterization missions (e.g., JWST/TPF) may be able to use these HZ boundaries to help guide their efforts to find habitable planets around main-sequence stars. (We acknowledge funding from NASA Astrobiology Institute's Virtual Planetary Laboratory, supported by NASA under cooperative agreement NNH05ZDA001C.)

  4. MASSES: An SMA Survey of Protostars Aimed at Understanding How Stars Gain Their Mass

    NASA Astrophysics Data System (ADS)

    Dunham, Michael; MASSES Team

    2016-01-01

    Low-mass stars form from the gravitational collapse of dense molecular cloud cores. While a general consensus picture of this collapse process has emerged, many details on how mass is transferred from cores to stars remain poorly understood. MASSES (Mass Assembly of Stellar Systems and their Evolution with the SMA), an SMA large-scale project, is surveying the complete population of Class 0 and Class I protostars in the nearby Perseus Molecular Cloud in order to reveal the interplay between fragmentation, conservation of angular momentum, and mass outflows in accreting mass and setting the final masses of stars. In this presentation I will highlight key science results from the first 1.5 years of observations.

  5. Episodic outflows from high-mass protostars

    SciTech Connect

    Mitchell, G.F.; Maillard, J.P.; Hasegawa, T.I. Canada-France-Hawaii Telescope Corp., Waimea, HI CNRS, Institut d'Astrophysique, Paris Duke University, Durham, NC )

    1991-04-01

    This paper examines the kinematics and physical properties of the outflowing gas from seven luminous deeply embedded young stellar objects or protostars: M8E-IR, GL 490, GL 2591, W3 IRS 5, NGC 7538 IRS 1, NGC 7538 IRS 9, and S140 IRS 1. The outflows are seen as blueshifted absorption features in lines of the fundamental band of CO. The CO lines seen in absorption are compared with CO lines seen in emission at mm wavelengths. New CO J = 2-1 emission-line data are presented for the first five of the sources. 60 refs.

  6. Determination of aflatoxins B1, B2, G1, G2 and ochratoxin A in animal feed by ultra high-performance liquid chromatography-tandem mass spectrometry.

    PubMed

    López Grío, Sergio José; Garrido Frenich, Antonia; Martínez Vidal, José Luis; Romero-González, Roberto

    2010-03-01

    A rapid and simple method was developed to determine aflatoxins B1, B2, G1, G2 and ochratoxin A in animal feed and pet foods by UHPLC-MS/MS. Because the complexity of the evaluated matrices, the proposed method is based on sonication extraction using an ACN/water mixture (80:20 v/v) followed by a clean-up step utilising C(18) as sorbent. Performance parameters of the method were evaluated, including linearity, trueness, precision and LOQ. Good linearity was found for all mycotoxins, with determination coefficients higher than 0.99 in the range considered, using matrix-matched calibration for quantification purposes. Recoveries ranged from 84 to 113%, with RSD lower than 20%, whereas LOQs were 5 microg/kg for the assayed mycotoxins. Finally, the method was successfully applied to the analysis of 19 real samples, detecting aflatoxin G2 in two samples at 13 and 17 microg/kg respectively, whereas the other mycotoxins were detected at trace levels (

  7. CCS and NH3 Emission Associated with Low-Mass Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    de Gregorio-Monsalvo, Itziar; Gómez, José F.; Suárez, Olga; Kuiper, Thomas B. H.; Rodríguez, Luis F.; Jiménez-Bailón, Elena

    2006-05-01

    In this work we present a sensitive and systematic single-dish survey of CCS emission (complemented with ammonia observations) at 1 cm, toward a sample of low- and intermediate-mass young star-forming regions known to harbor water maser emission, made with NASA's 70 m antenna at Robledo de Chavela, Spain. Out of the 40 star-forming regions surveyed in the CCS (21-10) line, only six low-mass sources show CCS emission: one transitional object between the prestellar and protostellar Class 0 phase (GF9-2), three Class 0 protostars (L1448-IRS3, L1448C, and B1-IRS), a Class I source (L1251A), and a young T Tauri star (NGC 2071 North). Since CCS is considered an ``early-time'' (<~105 yr) molecule, we explain these results by either proposing a revision of the classification of the age of NGC 2071 North and L1251A, or suggesting the possibility that the particular physical conditions and processes of each source affect the destruction/production of the CCS. No statistically significant relationship was found between the presence of CCS and parameters of the molecular outflows and their driving sources. Nevertheless, we found a significant relationship between the detectability of CCS and the ammonia peak intensity (higher in regions with CCS), but not with its integrated intensity. This tendency may suggest that the narrower ammonia line widths in the less turbulent medium associated with younger cores may compensate for the differences in ammonia peak intensity, rendering differences in integrated intensity negligible. From the CCS detection rate we derive a lifetime of this molecule of ~=(0.7-3)×104 yr in low-mass star-forming regions.

  8. Low-mass companions to Bright Giants

    NASA Astrophysics Data System (ADS)

    Niedzielski, A.; Wolszczan, A.; Nowak, G.; Adamów, M.; Deka, B.; Górecka, M.; Kowalik, K.

    2014-04-01

    systems evolution - the main goal of PTPS. The sample was optimized for HET and HRS. It contains relatively bright stars with V in the range of 9-12 mag, randomly distributed over the northern hemisphere. After 2-3 epochs or precise RV HET observations all stars with amplitudes exceeding the HET/HRS PSF FWHM - 5 km s-1 (SB1) or below 5?ERV - ˜ 20-50 m s (single) were rejected from further monitoring. Stars with significant cross-correlation profile variations were identified as SB2 and also excluded. All remaining 300 stars are systematically monitored in search for low-mass companions. Over a dozen stars with planetary-mass companions have already been discovered (Niedzielski et al. 2007, 2009a, b; Gettel et al. 2012a, b; Nowak et al. 2013). Here I will present our new results concerning the most luminous giants with log(L/LSun)> 2, presumably post Horizontal Branch stars.

  9. A Substellar-mass Protostar and its Outflow of IRAS 15398-3359 Revealed by Subarcsecond-resolution Observations of H2CO and CCH

    NASA Astrophysics Data System (ADS)

    Oya, Yoko; Sakai, Nami; Sakai, Takeshi; Watanabe, Yoshimasa; Hirota, Tomoya; Lindberg, Johan E.; Bisschop, Suzanne E.; Jørgensen, Jes K.; van Dishoeck, Ewine F.; Yamamoto, Satoshi

    2014-11-01

    Subarcsecond (0.''5) images of H2CO and CCH line emission have been obtained in the 0.8 mm band toward the low-mass protostar IRAS 15398-3359 in the Lupus 1 cloud as one of the Cycle 0 projects of the Atacama Large Millimeter/Submillimeter Array. We have detected a compact component concentrated in the vicinity of the protostar and a well-collimated outflow cavity extending along the northeast-southwest axis. The inclination angle of the outflow is found to be about 20°, or almost edge-on, based on the kinematic structure of the outflow cavity. This is in contrast to previous suggestions of a more pole-on geometry. The centrally concentrated component is interpreted by use of a model of the infalling rotating envelope with the estimated inclination angle and the mass of the protostar is estimated to be less than 0.09 M ⊙. Higher spatial resolution data are needed to infer the presence of a rotationally supported disk for this source, hinted at by a weak high-velocity H2CO emission associated with the protostar.

  10. A substellar-mass protostar and its outflow of IRAS 15398–3359 revealed by subarcsecond-resolution observations of H{sub 2}CO and CCH

    SciTech Connect

    Oya, Yoko; Sakai, Nami; Watanabe, Yoshimasa; Yamamoto, Satoshi; Sakai, Takeshi; Hirota, Tomoya; Lindberg, Johan E.; Bisschop, Suzanne E.; Jørgensen, Jes K.; Van Dishoeck, Ewine F.

    2014-11-10

    Subarcsecond (0.''5) images of H{sub 2}CO and CCH line emission have been obtained in the 0.8 mm band toward the low-mass protostar IRAS 15398–3359 in the Lupus 1 cloud as one of the Cycle 0 projects of the Atacama Large Millimeter/Submillimeter Array. We have detected a compact component concentrated in the vicinity of the protostar and a well-collimated outflow cavity extending along the northeast-southwest axis. The inclination angle of the outflow is found to be about 20°, or almost edge-on, based on the kinematic structure of the outflow cavity. This is in contrast to previous suggestions of a more pole-on geometry. The centrally concentrated component is interpreted by use of a model of the infalling rotating envelope with the estimated inclination angle and the mass of the protostar is estimated to be less than 0.09 M {sub ☉}. Higher spatial resolution data are needed to infer the presence of a rotationally supported disk for this source, hinted at by a weak high-velocity H{sub 2}CO emission associated with the protostar.

  11. DISK AND ENVELOPE STRUCTURE IN CLASS 0 PROTOSTARS. II. HIGH-RESOLUTION MILLIMETER MAPPING OF THE SERPENS SAMPLE

    SciTech Connect

    Enoch, Melissa L.; Duchene, Gaspard; Wright, Melvyn C. H.; Corder, Stuartt; Bolatto, Alberto D.; Teuben, Peter J.; Zauderer, B. Ashley; Culverhouse, Thomas L.; Lamb, James W.; Leitch, Erik M.; Muchovej, Stephen J.; Scott, Stephen L.; Kwon, Woojin; Marrone, Daniel P.; Perez, Laura M.

    2011-08-01

    We present high-resolution CARMA 230 GHz continuum imaging of nine deeply embedded protostars in the Serpens Molecular Cloud, including six of the nine known Class 0 protostars in Serpens. This work is part of a program to characterize disk and envelope properties for a complete sample of Class 0 protostars in nearby low-mass star-forming regions. Here, we present CARMA maps and visibility amplitudes as a function of uv-distance for the Serpens sample. Observations are made in the B, C, D, and E antenna configurations, with B configuration observations utilizing the CARMA Paired Antenna Calibration System. Combining data from multiple configurations provides excellent uv-coverage (4-500 k{lambda}), allowing us to trace spatial scales from 10{sup 2} to 10{sup 4} AU. We find evidence for compact disk components in all of the observed Class 0 protostars, suggesting that disks form at very early times (t < 0.2 Myr) in Serpens. We make a first estimate of disk masses using the flux at 50 k{lambda}, where the contribution from the envelope should be negligible, assuming an unresolved disk. The resulting disk masses range from 0.04 M{sub sun} to 1.7 M{sub sun}, with a mean of approximately 0.2 M{sub sun}. Our high-resolution maps are also sensitive to binary or multiple sources with separations {approx}> 250 AU, but significant evidence of multiplicity on scales <2000 AU is seen in only one source.

  12. An IRAS Hires study of low mass star formation in the Taurus molecular ring

    NASA Technical Reports Server (NTRS)

    Terebey, Susan; Surace, Jason A.

    1994-01-01

    The Taurus molecular cloud supposedly has no star clusters but only isolated star formation. However, the Infrared Astronomical Satellite (IRAS) shows us that a small star cluster is currently forming in Taurus. Most of the sources are deeply embedded and are probably low-mass protostars. We use High Resolution (HiRes) images of the IRAS data from the Infrared Processing and Analysis Center (IPAC) to look for additional infrared members of the cluster. We also investigate the question of whether the infrared emission matches predictions for protostellar sources by examining whether the dust emission is resolved on scales of one arcminute (approx. 10(exp 17) cm). With the exception of a luminous visible star, HD 29647, we find that the sources L1527, TMC1A, TMC1, TMC1C, tMR1, and IC2087 are unresolved in the HiRes images at 60 microns. Further analysis of IC2087 shows that it is unresolved at all four IRAS wavelengths.

  13. Protostars, multiplicity, and disk evolution in the Corona Australis region: a Herschel Gould Belt Study

    NASA Astrophysics Data System (ADS)

    Sicilia-Aguilar, A.; Henning, T.; Linz, H.; André, P.; Stutz, A.; Eiroa, C.; White, G. J.

    2013-03-01

    Context. The CrA region and the Coronet cluster form a nearby (138 pc), young (1-2 Myr) star-forming region that hosts a moderate population of Class I, II, and III objects. Aims: We study the structure of the cluster and the properties of the protostars and protoplanetary disks in the region. Methods: We present Herschel PACS photometry at 100 and 160 μm, obtained as part of the Herschel Gould Belt Survey. The Herschel maps reveal the cluster members within the cloud with high sensitivity and high dynamic range. Results: Many of the cluster members are detected, including some embedded, very low-mass objects, several protostars (some of them extended), and substantial emission from the surrounding molecular cloud. Herschel also reveals some striking structures, such as bright filaments around the IRS 5 protostar complex and a bubble-shaped rim associated with the Class I object IRS 2. The disks around the Class II objects display a wide range of mid- and far-IR excesses consistent with different disk structures. We have modeled the disks with the RADMC radiative transfer code to quantify their properties. Some of them are consistent with flared, massive, relatively primordial disks (S CrA, T CrA). Others display significant evidence for inside-out evolution, consistent with the presence of inner holes/gaps (G-85, G-87). Finally, we found disks with a dramatic small dust depletion (G-1, HBC 677) that, in some cases, could be related to truncation or to the presence of large gaps in a flared disk (CrA-159). The derived masses for the disks around the low-mass stars are found to be below the typical values in Taurus, in agreement with previous Spitzer observations. Conclusions: The Coronet cluster presents itself as an interesting compact region that contains both young protostars and very evolved disks. The Herschel data provide sufficient spatial resolution to detect small-scale details, such as filamentary structures or spiral arms associated with multiple star

  14. Optimization and validation of a HPLC method for simultaneous determination of aflatoxin B1, B2, G1, G2, ochratoxin A and zearalenone using an experimental design.

    PubMed

    Rahmani, Anosheh; Selamat, Jinap; Soleimany, Farhang

    2011-01-01

    A reversed-phase HPLC optimization strategy is presented for investigating the separation and retention behavior of aflatoxin B1, B2, G1, G2, ochratoxin A and zearalenone, simultaneously. A fractional factorial design (FFD) was used to screen the significance effect of seven independent variables on chromatographic responses. The independent variables used were: (X1) column oven temperature (20-40°C), (X2) flow rate (0.8-1.2 ml/min), (X3) acid concentration in aqueous phase (0-2%), (X4) organic solvent percentage at the beginning (40-50%), and (X5) at the end (50-60%) of the gradient mobile phase, as well as (X6) ratio of methanol/acetonitrile at the beginning (1-4) and (X7) at the end (0-1) of gradient mobile phase. Responses of chromatographic analysis were resolution of mycotoxin peaks and HPLC run time. A central composite design (CCD) using response surface methodology (RSM) was then carried out for optimization of the most significant factors by multiple regression models for response variables. The proposed optimal method using 40°C oven temperature, 1 ml/min flow rate, 0.1% acetic acid concentration in aqueous phase, 41% organic phase (beginning), 60% organic phase (end), 1.92 ratio of methanol to acetonitrile (beginning) and 0.2 ratio (end) for X1-X7, respectively, showed good prediction ability between the experimental data and predictive values throughout the studied parameter space. Finally, the optimized method was validated by measuring the linearity, sensitivity, accuracy and precision parameters, and has been applied successfully to the analysis of spiked cereal samples. PMID:21598138

  15. Application of dispersive liquid-liquid microextraction for the determination of aflatoxins B1, B2, G1 and G2 in cereal products.

    PubMed

    Campone, Luca; Piccinelli, Anna Lisa; Celano, Rita; Rastrelli, Luca

    2011-10-21

    The application of dispersive liquid-liquid microextraction (DLLME) technique for the rapid analysis of aflatoxins B(1), B(2), G(1) and G(2) in maize, rice and wheat products has been evaluated. After extraction of aflatoxins from cereal matrices with a mixture of methanol/water 8:2 (v/v), the analytes were rapidly transferred from the extract to another small volume of organic solvent, chloroform, by DLLME. Aflatoxins were determined using high performance liquid chromatography with florescence detection and photochemical post-column derivatization. Parameters affecting both extraction and DLLME procedures, such as extraction solvent, type and volume of DLLME extractant, volume of water and salt effect, were systematically investigated and optimized to achieve the best extraction efficiency. Under the optimal experimental conditions, the whole analytical method provides enrichment factors around 2.5 times and detection limits (0.01-0.17 μg kg(-1)) below the maximum levels imposed by current regulation for aflatoxins in cereals and cereal products intended for direct human consumption. Recoveries (67-92%) and repeatability (RSD<10, n=3), tested in three different cereal matrices, meet the performance criteria required by EC Regulation No. 401/2006 for the determination of the levels of mycotoxins in foodstuffs. The proposed method was successfully applied to the analysis of retail cereal products with quantitative results comparable to the immunoaffinity chromatography (IAC). The main advantages of developed method are the simplicity of operation, the rapidity to achieve a very high sample throughput and low cost. PMID:21636088

  16. Simultaneous determination of aflatoxin B(1), B(2), G(1), G(2), ochratoxin A, and sterigmatocystin in traditional Chinese medicines by LC-MS-MS.

    PubMed

    Zheng, Runsheng; Xu, Hui; Wang, Wenli; Zhan, Ruoting; Chen, Weiwen

    2014-05-01

    In this paper we describe a rapid, simple, and costeffective liquid chromatography–tandem mass spectrometric (LC–MS–MS) method for simultaneous analysis of aflatoxin B1, B2, G1, and G2, ochratoxin A, and sterigmatocystin in 25 traditional Chinese medicines (TCMs). The method is based on single extraction with 84:16 (v/v) acetonitrile–water then analysis of the diluted crude extract without further clean-up. Chromatographic separation was achieved on a C18 column, with a mobile phase gradient prepared from aqueous 4 mmol L−1 ammonium acetate–0.1 % formic acid and methanol. Quantification of the analytes was by selective reaction monitoring (SRM) on a triple-quadrupole mass spectrometer in positive-ionization mode. Special focus was on investigating and reducing matrix effects to improve accuracy. The established method was validated by determination of linearity (r>0.995), sensitivity (limits of quantification 1.6–25.0 ng L−1), apparent recovery (84.8–110.6 %), extraction recovery (83.6–106.1 %), and precision (relative standard deviation ≤9.9 %) for two representative TCMs, Semen Armeniacae Amarae and Radix Pseudostellariae. The applicability of the method to TCMs other than these was further investigated, and 23 other TCMs with acceptable matrix effects (80.2–118.6 %) were screened. The validated method was finally used to assess mycotoxin contamination of 244 samples of 25 TCMs collected from local hospitals and TCM pharmacies. Aflatoxin B1 and ochratoxin A were detected in 5.3 % of the samples. Sterigmatocystin, the most prevalent mycotoxin contaminant, was present in 26.2 % of the samples tested; this has not been reported previously. The results of this work imply greater attention should be devoted to evaluation of the potential hazard caused by sterigmatocystin in TCMs. PMID:24658469

  17. [Determination of aflatoxin B1, B2, G1, G2 in armeniacae semen amarum by high-performance liquid chromatography-tandem mass spectrometry].

    PubMed

    Zheng, Run-Sheng; Xu, Hui; Wang, Wen-Li; Zhan, Ruo-Ting; Chen, Wei-Wen

    2013-10-01

    A simple, rapid and cost-effective high-performance liquid chromatography-tandem mass spectrometry (LC-MS/ MS) method was established for simultaneous determination of aflatoxins (AFB1, AFB2, AFG1, AFG2) in Armeniacae Semen Amarum and the application was performance in 11 samples collected from different markets, medical stores and hospitals. The sample was extracted with 84% acetonitrile/water and 250 microL extraction was directly injected into a LC-MS/MS system without further purification procedure after being redissolved with methanol. The LC separation was performed on a C18 column with a linear gradient elution program of 4 mmol x L(-1) NH4 Ac-0.1% formic acid solution and menthol as the mobile phase. Selected reaction monitoring (SRM) was used for selective determination of the four aflatoxins on a triple quadruple mass spectrometer, which was operated in positive ionization modes. All the four aflatoxins showed a good linear relationship with r > 0.999 0, the average recoveries were between 87.88% and 102.9% and the matrix effect was ranged from 90.71% to 99.30% in low, intermediate and high levels. Furthermore, the higher recovery was obtained by the method reported in this study, comparing to the cleanup procedure with the Mycosep 226 purification column. Eleven samples collected were detected and the contamination levels of the AFB1 were between 1.590-2.340 microg x kg(-1) and the AF (B1 + B2 + G1 + G2) was ranged from 2.340 to 3.340 microg x kg(-1). In summary, the developed method was suitable to detect and screen AFB1, AFB2, AFG1, AFG2 in Armeniacae Semen Amarum. PMID:24490568

  18. GIANT PLANET FORMATION BY DISK INSTABILITY IN LOW MASS DISKS?

    SciTech Connect

    Boss, Alan P.

    2010-12-20

    Forming giant planets by disk instability requires a gaseous disk that is massive enough to become gravitationally unstable and able to cool fast enough for self-gravitating clumps to form and survive. Models with simplified disk cooling have shown the critical importance of the ratio of the cooling to the orbital timescales. Uncertainties about the proper value of this ratio can be sidestepped by including radiative transfer. Three-dimensional radiative hydrodynamics models of a disk with a mass of 0.043 M{sub sun} from 4 to 20 AU in orbit around a 1 M{sub sun} protostar show that disk instabilities are considerably less successful in producing self-gravitating clumps than in a disk with twice this mass. The results are sensitive to the assumed initial outer disk (T{sub o}) temperatures. Models with T{sub o} = 20 K are able to form a single self-gravitating clump, whereas models with T{sub o} = 25 K form clumps that are not quite self-gravitating. These models imply that disk instability requires a disk with a mass of at least {approx}0.043 M{sub sun} inside 20 AU in order to form giant planets around solar-mass protostars with realistic disk cooling rates and outer-disk temperatures. Lower mass disks around solar-mass protostars must rely upon core accretion to form inner giant planets.

  19. The rotation of very low mass objects

    NASA Astrophysics Data System (ADS)

    Scholz, Alexander

    2004-10-01

    This dissertation contains an investigation of the rotation of very low mass objects, i.e. Brown Dwarfs and stars with masses <0.4 MS. Today, it is well-established that there are large populations of such VLM objects in open clusters and in the field, but our knowledge about their physical properties and evolution is still very limited. Contrary to their solar-mass siblings, VLM objects are fully convective throughout their evolution. Thus, they are not able to form a large-scale magnetic field like for example the sun. The magnetic field, in turn, is crucial for the regulation of rotation: Magnetic interaction between star and circumstellar disk ("disk-locking") and angular momentum losses through stellar winds have dominant influence on the rotational evolution. Thus, we can expect major differences in the rotational behaviour of VLM objects and solar-mass stars. The best method to investigate stellar rotation is to measure rotation periods. If a star exhibits surface features which are asymmetrically distributed, its brightness may be modulated with the rotation period. Thus, this dissertation is based on the analysis of photometric time series. Open clusters are an ideal environment for such a project, since they enable one to follow many objects at the same time. Additionally, they allow one to investigate the age and mass dependence of rotation, because distance and age of the clusters are known in good approximation. For this thesis, five open clusters were observed, which span an age range from 3 to 750 Myr. In three of them (SigmaOri, EpsilonOri, IC4665), VLM objects were identified by means of colour magnitude diagrams. The candidate lists for these three regions comprise at least 100 objects, for which photometry in at least three wavelength bands is available. About a fifth to a third of these candidates could be contaminating field stars in the fore- or background of the clusters. For the remaining two clusters (Pleiades and Praesepe), objects from

  20. Evolution of Mass Outflow in Protostars

    NASA Astrophysics Data System (ADS)

    Watson, Dan M.; Calvet, Nuria P.; Fischer, William J.; Forrest, W. J.; Manoj, P.; Megeath, S. Thomas; Melnick, Gary J.; Najita, Joan; Neufeld, David A.; Sheehan, Patrick D.; Stutz, Amelia M.; Tobin, John J.

    2016-09-01

    We have surveyed 84 Class 0, Class I, and flat-spectrum protostars in mid-infrared [Si ii], [Fe ii], and [S i] line emission, and 11 of these in far-infrared [O i] emission. We use the results to derive their mass outflow rates, {\\dot{M}}w. Thereby we observe a strong correlation of {\\dot{M}}w with bolometric luminosity, and with the inferred mass accretion rates of the central objects, {\\dot{M}}a, which continues through the Class 0 range the trend observed in Class II young stellar objects. Along this trend from large to small mass flow rates, the different classes of young stellar objects lie in the sequence Class 0–Class I/flat-spectrum–Class II, indicating that the trend is an evolutionary sequence in which {\\dot{M}}a and {\\dot{M}}w decrease together with increasing age, while maintaining rough proportionality. The survey results include two that are key tests of magnetocentrifugal outflow-acceleration mechanisms: the distribution of the outflow/accretion branching ratio b={\\dot{M}}w/{\\dot{M}}a, and limits on the distribution of outflow speeds. Neither rules out any of the three leading outflow-acceleration, angular-momentum-ejection mechanisms, but they provide some evidence that disk winds and accretion-powered stellar winds (APSWs) operate in many protostars. An upper edge observed in the branching-ratio distribution is consistent with the upper bound of b = 0.6 found in models of APSWs, and a large fraction (31%) of the sample have a branching ratio sufficiently small that only disk winds, launched on scales as large as several au, have been demonstrated to account for them.

  1. THE BINARY FRACTION OF LOW-MASS WHITE DWARFS

    SciTech Connect

    Brown, Justin M.; Kilic, Mukremin; Brown, Warren R.; Kenyon, Scott J.

    2011-04-01

    We describe spectroscopic observations of 21 low-mass ({<=}0.45 M{sub sun}) white dwarfs (WDs) from the Palomar-Green survey obtained over four years. We use both radial velocities and infrared photometry to identify binary systems, and find that the fraction of single, low-mass WDs is {<=}30%. We discuss the potential formation channels for these single stars including binary mergers of lower-mass objects. However, binary mergers are not likely to explain the observed number of single low-mass WDs. Thus, additional formation channels, such as enhanced mass loss due to winds or interactions with substellar companions, are likely.

  2. HIGH RESOLUTION H{alpha} IMAGES OF THE BINARY LOW-MASS PROPLYD LV 1 WITH THE MAGELLAN AO SYSTEM

    SciTech Connect

    Wu, Y.-L.; Close, L. M.; Males, J. R.; Follette, K.; Morzinski, K.; Kopon, D.; Rodigas, T. J.; Hinz, P.; Puglisi, A.; Esposito, S.; Pinna, E.; Riccardi, A.; Xompero, M.; Briguglio, R.

    2013-09-01

    We utilize the new Magellan adaptive optics system (MagAO) to image the binary proplyd LV 1 in the Orion Trapezium at H{alpha}. This is among the first AO results in visible wavelengths. The H{alpha} image clearly shows the ionization fronts, the interproplyd shell, and the cometary tails. Our astrometric measurements find no significant relative motion between components over {approx}18 yr, implying that LV 1 is a low-mass system. We also analyze Large Binocular Telescope AO observations, and find a point source which may be the embedded protostar's photosphere in the continuum. Converting the H magnitudes to mass, we show that the LV 1 binary may consist of one very-low-mass star with a likely brown dwarf secondary, or even plausibly a double brown dwarf. Finally, the magnetopause of the minor proplyd is estimated to have a radius of 110 AU, consistent with the location of the bow shock seen in H{alpha}.

  3. Direct Search for Low Mass Dark Matter Particles with CCDs

    DOE PAGESBeta

    Barreto, J.; Cease, H.; Diehl, H. T.; Estrada, J.; Flaugher, B.; Harrison, N.; Jones, J.; Kilminster, B.; Molina, J.; Smith, J.; et al

    2012-05-15

    A direct dark matter search is performed using fully-depleted high-resistivity CCD detectors. Due to their low electronic readout noise (RMS ~7 eV) these devices operate with a very low detection threshold of 40 eV, making the search for dark matter particles with low masses (~5 GeV) possible. The results of an engineering run performed in a shallow underground site are presented, demonstrating the potential of this technology in the low mass region.

  4. The origin of low-mass white dwarfs

    SciTech Connect

    Rebassa-Mansergas, A.; Schreiber, M. R.; Gaensicke, B. T.; Girven, J.; Gomez-Moran, A. Nebot

    2010-11-23

    We present white dwarf mass distributions of a large sample of post common-envelope binaries and wide white dwarf main sequence binaries and demonstrate that these distributions are statistically independent. While the former contains a much larger fraction of low-mass white dwarfs, the latter is similar to single white dwarf mass distributions. Taking into account observational biases we also show that the majority of low-mass white dwarfs are formed in close binaries.

  5. Circumstellar ring formation in rapidly rotating protostars

    SciTech Connect

    Williams, H.A.; Tohline, J.E.

    1988-11-01

    Rapidly rotating, self-gravitating polytropes with polytropic indices n = 0.8 and n = 1.8 are studied using a three-dimensional hydrodynamic computer program. The two models are shown as they evolve to extremely nonlinear amplitudes, ending in a type of fission. It is found that the low-mass, roughly axisymmetric ring appears to be dynamically stable, but capable of condensing into planets over a much longer time scale. 34 references.

  6. METHYL CYANIDE OBSERVATIONS TOWARD MASSIVE PROTOSTARS

    SciTech Connect

    Rosero, V.; Hofner, P.; Kurtz, S.; Bieging, J.; Araya, E. D.

    2013-07-01

    We report the results of a survey in the CH{sub 3}CN J = 12 {yields} 11 transition toward a sample of massive proto-stellar candidates. The observations were carried out with the 10 m Submillimeter Telescope on Mount Graham, AZ. We detected this molecular line in 9 out of 21 observed sources. In six cases this is the first detection of this transition. We also obtained full beam sampled cross-scans for five sources which show that the lower K-components can be extended on the arcminute angular scale. The higher K-components, however, are always found to be compact with respect to our 36'' beam. A Boltzmann population diagram analysis of the central spectra indicates CH{sub 3}CN column densities of about 10{sup 14} cm{sup -2}, and rotational temperatures above 50 K, which confirms these sources as hot molecular cores. Independent fits to line velocity and width for the individual K-components resulted in the detection of an increasing blueshift with increasing line excitation for four sources. Comparison with mid-infrared (mid-IR) images from the SPITZER GLIMPSE/IRAC archive for six sources show that the CH{sub 3}CN emission is generally coincident with a bright mid-IR source. Our data clearly show that the CH{sub 3}CN J = 12 {yields} 11 transition is a good probe of the hot molecular gas near massive protostars, and provide the basis for future interferometric studies.

  7. Star Formation near Berkeley 59: Embedded Protostars

    NASA Astrophysics Data System (ADS)

    Rosvick, J. M.; Majaess, D.

    2013-12-01

    A group of suspected protostars in a dark cloud northwest of the young (~2 Myr) cluster Berkeley 59 and two sources in a pillar south of the cluster have been studied in order to determine their evolutionary stages and ascertain whether their formation was triggered by Berkeley 59. Narrowband near-infrared observations from the Observatoire du Mont Mégantic, 12CO (J = 3-2) and SCUBA-2 (450 and 850 μm) observations from the JCMT, 2MASS, and WISE images, and data extracted from the IPHAS survey catalog were used. Of 12 sources studied, two are Class I objects, while three others are flat/Class II, one of which is a T Tauri candidate. A weak CO outflow and two potential starless cores are present in the cloud, while the pillar possesses substructure at different velocities, with no outflows present. The CO spectra of both regions show peaks in the range v LSR = -15 to -17 km s-1, which agrees with the velocity adopted for Berkeley 59 (-15.7 km s-1), while spectral energy distribution models yield an average interstellar extinction AV and distance of 15 ± 2 mag and 830 ± 120 pc, respectively, for the cloud, and 6.9 mag and 912 pc for the pillar, indicating that the regions are in the same vicinity as Berkeley 59. The formation of the pillar source appears to have been triggered by Berkeley 59. It is unclear whether Berkeley 59 triggered the association's formation.

  8. Primordial stellar evolution - The protostar phase

    NASA Technical Reports Server (NTRS)

    Stahler, S. W.; Palla, F.; Salpeter, E. E.

    1986-01-01

    The structure and evolution of a protostar forming from a cloud composed of pure hydrogen and helium gas are calculated. Using an accretion rate of 0.0044 solar mass/yr, the collapse of the cloud is followed numerically as a sequence of steady state accretion flows onto the hydrostatic core, which grows from an initial mass of 0.01 solar mass to 10.5 solar masses. The core is surrounded by an optically thick radiative precursor for most of its evolution. The core radius reaches 47 solar radii when the mass is 1 solar mass. For sufficiently massive cores, the deep interior contracts strongly, driving out a 'luminosity wave' which reaches the surface when the mass is 8 solar masses. This results in a large increase in core radius, the establishment of surface convection, and the disappearance of the radiative precursor. The dependence of core radius on the mass and accretion rate is analytically derived, and a new table or Rosseland mean opacities for metal-free gas is presented.

  9. Pulsed accretion in a variable protostar.

    PubMed

    Muzerolle, James; Furlan, Elise; Flaherty, Kevin; Balog, Zoltan; Gutermuth, Robert

    2013-01-17

    Periodic increases in luminosity arising from variable accretion rates have been predicted for some pre-main-sequence close binary stars as they grow from circumbinary disks. The phenomenon is known as pulsed accretion and can affect the orbital evolution and mass distribution of young binaries, as well as the potential for planet formation. Accretion variability is a common feature of young stars, with a large range of amplitudes and timescales as measured from multi-epoch observations at optical and infrared wavelengths. Periodic variations consistent with pulsed accretion have been seen in only a few young binaries via optical accretion tracers, albeit intermittently with accretion luminosity variations ranging from zero to 50 per cent from orbit to orbit. Here we report that the infrared luminosity of a young protostar (of age about 10(5) years) increases by a factor of ten in roughly one week every 25.34 days. We attribute this to pulsed accretion associated with an unseen binary companion. The strength and regularity of this accretion signal is surprising; it may be related to the very young age of the system, which is a factor of ten younger than the other pulsed accretors previously studied. PMID:23283175

  10. Fundamental Properties of Low-Mass Stars and Brown Dwarfs

    SciTech Connect

    Liu, Michael C.; Dupuy, Trent J.; Stassun, Keivan G.; Allard, France; Blake, Cullen H.; Bonnefoy, M.; Cody, Ann Marie; Kraus, Adam; Day-Jones, A. C.; Lopez-Morales, Mercedes

    2009-02-16

    Precise measurements of the fundamental properties of low-mass stars and brown dwarfs are key to understanding the physics underlying their formation and evolution. While there has been great progress over the last decade in studying the bulk spectrophotometric properties of low-mass objects, direct determination of their masses, radii, and temperatures have been very sparse. Thus, theoretical predictions of low-mass evolution and ultracool atmospheres remain to be rigorously tested. The situation is alarming given that such models are widely used, from the determination of the low-mass end of the initial mass function to the characterization of exoplanets.An increasing number of mass, radius, and age determinations are placing critical constraints on the physics of low-mass objects. A wide variety of approaches are being pursued, including eclipsing binary studies, astrometric-spectroscopic orbital solutions, interferometry, and characterization of benchmark systems. In parallel, many more systems suitable for concerted study are now being found, thanks to new capabilities spanning both the very widest (all-sky surveys) and very narrowest (diffraction-limited adaptive optics) areas of the sky. This Cool Stars 15 splinter session highlighted the current successes and limitations of this rapidly growing area of precision astrophysics.

  11. 2MASS J17112318-2724315: A DEEPLY EMBEDDED LOW-MASS PROTOSTELLAR SYSTEM IN THE B59 MOLECULAR CLOUD

    SciTech Connect

    Riaz, B.; Martin, E. L.; Bouy, H.; Tata, R.

    2009-08-01

    We present near-infrared observations of the low-mass deeply embedded Class 0/I system 2MASS J17112318-2724315 (2M171123) in the B59 molecular cloud. Bright scattered light nebulosity is observed toward this source in the K{sub s} images, that seems to trace the edges of an outflow cavity. We report the detection of a low-luminosity protostar 2M17112255-27243448 (2M17112255) that lies {approx}8'' ({approx}1000 AU) from 2M171123. This is a Class I system, as indicated by its 2-8 {mu}m slope and Infrared Array Camera colors, with an estimated internal luminosity of {approx}0.3 L{sub sun}. We estimate a mass of {approx}0.12-0.25 M{sub sun} for this source, at an age of 0.1-1 Myr. Also presented is detailed modeling of the 2M171123 system. The best-fit parameters indicate a large envelope density of the order of {approx}10{sup -13} g cm{sup -3}, and an intermediate inclination between 53 deg. and 59 deg. The observed K{sub s} -band variability for this system could be explained by slight variability in the mass infall rate between 2.5E-5 and 1.8E-5 M{sub sun} yr{sup -1}. The protostar 2M171123 exhibits a rarely observed absorption feature near 11.3 {mu}m within its 10 {mu}m silicate band. We find a strong correlation between the strength in this 11.3 {mu}m 'edge' and the H{sub 2}O-ice column density, indicating the origin of this feature in the thickness of the ice mantle over the silicate grains.

  12. Water and methanol in low-mass protostellar outflows: gas-phase synthesis, ice sputtering and destruction

    NASA Astrophysics Data System (ADS)

    Suutarinen, A. N.; Kristensen, L. E.; Mottram, J. C.; Fraser, H. J.; van Dishoeck, E. F.

    2014-05-01

    Water in outflows from protostars originates either as a result of gas-phase synthesis from atomic oxygen at T ≳ 200 K, or from sputtered ice mantles containing water ice. We aim to quantify the contribution of the two mechanisms that lead to water in outflows, by comparing observations of gas-phase water to methanol (a grain surface product) towards three low-mass protostars in NGC 1333. In doing so, we also quantify the amount of methanol destroyed in outflows. To do this, we make use of James Clerk Maxwell Telescope and Herschel-Heterodyne Instrument for the Far-Infrared data of H2O, CH3OH and CO emission lines and compare them to RADEX non-local thermodynamic equilibrium excitation simulations. We find up to one order of magnitude decrease in the column density ratio of CH3OH over H2O as the velocity increases in the line wings up to ˜15 km s-1. An independent decrease in X(CH3OH) with respect to CO of up to one order of magnitude is also found in these objects. We conclude that gas-phase formation of H2O must be active at high velocities (above 10 km s-1 relative to the source velocity) to re-form the water destroyed during sputtering. In addition, the transition from sputtered water at low velocities to form water at high velocities must be gradual. We place an upper limit of two orders of magnitude on the destruction of methanol by sputtering effects.

  13. Class I methanol masers in low-mass star-forming regions

    NASA Astrophysics Data System (ADS)

    Kalenskii, S. V.; Kurtz, S.; Bergman, P.

    2013-02-01

    Results of observations of Class I methanol masers in regions of low-mass star formation (MMIL) are summarized and analyzed. Four masers were detected at 44, 84, and 95 GHz towards "chemically active" bipolar outflows in the low-mass star-forming regions NGC1333 I4A, NGC 1333 I2A, HH 25, and L1157. Another maser was found at 36 GHz towards a similar outflow in NGC 2023. Thus, all the detected MMILs are associated with chemically active outflows. The brightness temperatures of the strongest 44-GHz maser spots in NGC 1333 I4A, HH 25, and L1157 exceed 2000 K, whereas the brightness temperature in NGC 1333 I2A is only 176 K, although a rotational-diagram analysis shows that this last source is also amaser. The flux densities of the newly detectedmasers are no higher than 18 Jy, and are much lower than those of strong masers in regions of high-mass star formation (MMIH). The MMIL luminosities match the maser luminosity-protostar luminosity relation established earlier for MMIHs. No MMIL variability was detected in 2004-2011. The radial velocities of the newly detected masers are close to the systemic velocities of the associated regions, except for NGC 2023, where the maser radial velocity is lower than the systemic velocity by approximately 3.5 km/s. Thus, the main MMILproperties are similar to those of MMIHs. MMILs are likely to be an extension of the MMIH population toward lower luminosities of both the masers and the associated young stellar objects. The results of VLA observations of MMILs can be explained using a turbulent-cloud model, which predicts that compact maser spots can arise in extended sources because the coherence lengths along some directions randomly appear to be longer than the mean coherence length in a turbulent velocity field. However, one must assume that the column density of methanol towardM1, the strongest maser in L1157, is appreciably higher than the mean column density of the clump B0a where the maser arises. The shape of the maser lines

  14. Low-Mass Stirling Convertor Assembly Progress Update

    NASA Astrophysics Data System (ADS)

    Qiu, Songgang; Augenblick, John E.; Redinger, Darin L.

    2006-01-01

    Infinia is developing the next generation of space-ready Stirling Convertor Assemblies. Infinia has previously proposed a Low-Mass Stirling Convertor Assembly (SCA) design employing a flux-concentrating, moving-iron linear alternator. This paper describes further development of that proposed machine, including additional improvements and advancements. One significant change is a new, lighter-weight moving-magnet alternator design. Infinia has shown progress in the low mass design's development and testing: namely in the area of flexure spring rates, welding techniques on the flange, and a change to the alternator configuration. Progress has been made with the flat-top heater head design and its capabilities, as well. The changes described in this paper will significantly reduce the mass and increase the power density of the low-mass design.

  15. Determination of aflatoxins B1, B2, G1, and G2 in olive oil, peanut oil, and sesame oil using immunoaffinity column cleanup, postcolumn derivatization, and liquid chromatography with fluorescence detection: first action 2013.05.

    PubMed

    Bao, Lei; Liang, Chengzhu; Trucksess, Mary W; Xu, Yanli; Lv, Ning; Wu, Zhenxing; Jing, Ping; Fry, Fred S

    2013-01-01

    A collaborative study of a method for determination of aflatoxins (AFs) B1, B2, G1, and G2 in olive oil, peanut oil, and sesame oil using immunoaffinity column cleanup, postcolumn derivatization, and LC with fluorescence detection, previously published in J. AOAC Int. 95, 1689-1700 (2012), was approved as First Action 2013.05 on March 29, 2013 by the Method-Centric Committee for Aflatoxins in Edible Oils. The method uses methanol for extraction followed by filtration. The extract is applied to an immunoaffinity column with antibodies specific for AFs, which are then eluted from the column with a methanol solution. Determination and quantification occur using RP-LC with fluorescence detection after postcolumn derivatization. The average recovery of AFs in olive, peanut, and sesame oils in spiked samples (levels between 2.0 and 20.0 microg/kg) ranged from 84 to 92%. The recoveries for AFs B1, B2, G1, and G2 were 86-93, 89-95, 85-97, and 76-85%, respectively. Within-laboratory RSD (RSDr) values for AFs ranged from 3.4 to 10.2%. RSDr values forAF B1, B2, G1, and G2 were 3.5-10.9, 3.2-9.5, 6.5-14.9, and 4.8-14.2%, respectively. Between-laboratory RSD (RSDR) values for AFs were 6.1-14.5%. RSD, values for AFs B1, B2, G1, and G2 were 7.5-15.4, 7.1-14.6, 10.8-18.1, and 7.6-23.7%, respectively. Horwitz ratio values were < or =2 for the analytes in the three matrixes. PMID:24282940

  16. Composition of the Silicates around Evolved Stars and Protostars

    NASA Astrophysics Data System (ADS)

    Demyk, K.; Dartois, E.; Wiesemeyer, H.; Jones, A.; D'Hendecourt, L.; Jourdain de Muizon, M.; Heras, A. M.

    2000-11-01

    We present a study of the composition of the silicates around five evolved stars and three high-mass protostars. Around evolved stars, the oxygen-rich dust is composed of amorphous olivine, crystalline silicates (enstatite, forsterite, diopside) and some oxides (FeO, Al2O3). Using a radiative transfer code we have modelled the SED of two OH/IR stars. We estimate that the amount of crystalline silicates in these objects is of the order of 20%. Around protostars, the dust is composed of porous pyroxene and/or aluminosilicate grains containing iron oxide. We calculate that at most 1-2% of the dust mass is crystalline. The newly formed dust around evolved stars has a different structure and composition from the old dust found around protostars. This implies that some mechanism, which remains to be found, occurs during the grain lifetime and alters the chemical composition and structure of the grains.

  17. The Infrared Signature of Accretion Luminosity in Protostars

    NASA Astrophysics Data System (ADS)

    Terebey, Susan; Villarama, Ethan G.; Flores-Rivera, Lizxandra

    2016-06-01

    Mass accretion from the disk onto the star is an important mechanism by which a star increases in mass during the formation phase. If the mass accretion rate is time variable then the brightness of the star should also change with time. We use the HOCHUNK3D radiative transfer code to investigate how disk accretion rate (Mdot) affects the protostar spectral energy distribution (SED). The biggest changes in brightness occur at infrared wavelengths ranging from approximately 5 to 100 microns. The results show that the protostar luminosity doubles from 1 to 2 L⊙ when the disk accretion rate is increased to Mdot=3.0e-7 M⊙/year. We conclude that the models are a useful tool to study mass accretion rates and time variability in protostars.

  18. FORMALDEHYDE AND METHANOL DEUTERATION IN PROTOSTARS: FOSSILS FROM A PAST FAST HIGH-DENSITY PRE-COLLAPSE PHASE

    SciTech Connect

    Taquet, V.; Ceccarelli, C.; Kahane, C.

    2012-03-20

    Extremely high deuteration of several molecules has been observed around low-mass protostars for a decade. Among them, formaldehyde and methanol present particularly high deuteration, with observations of abundant doubly and triply deuterated forms. Both species are thought to be mainly formed on interstellar grains during the low-temperature and dense pre-collapse phase by H and D atom additions on the iced CO. We present here a theoretical study of the formaldehyde and methanol deuteration obtained with our gas-grain model, GRAINOBLE. This model takes into account the multilayer nature of the mantle and explores the robustness of the results against the uncertainties of poorly constrained chemical and surface model parameters. The comparison of the model predictions with the observations leads to two major results: (1) the observed high deuteration is obtained during the last phase of the pre-collapse stage, when the density reaches {approx}5 Multiplication-Sign 10{sup 6} cm{sup -3}, and this phase is fast, lasting only several thousands years; and (2) D and H abstraction and substitution reactions are crucial in making up the observed deuteration ratios. This work shows the power of chemical composition as a tool to reconstruct the past history of protostars.

  19. Formaldehyde and Methanol Deuteration in Protostars: Fossils from a Past Fast High-density Pre-collapse Phase

    NASA Astrophysics Data System (ADS)

    Taquet, V.; Ceccarelli, C.; Kahane, C.

    2012-03-01

    Extremely high deuteration of several molecules has been observed around low-mass protostars for a decade. Among them, formaldehyde and methanol present particularly high deuteration, with observations of abundant doubly and triply deuterated forms. Both species are thought to be mainly formed on interstellar grains during the low-temperature and dense pre-collapse phase by H and D atom additions on the iced CO. We present here a theoretical study of the formaldehyde and methanol deuteration obtained with our gas-grain model, GRAINOBLE. This model takes into account the multilayer nature of the mantle and explores the robustness of the results against the uncertainties of poorly constrained chemical and surface model parameters. The comparison of the model predictions with the observations leads to two major results: (1) the observed high deuteration is obtained during the last phase of the pre-collapse stage, when the density reaches ~5 × 106 cm-3, and this phase is fast, lasting only several thousands years; and (2) D and H abstraction and substitution reactions are crucial in making up the observed deuteration ratios. This work shows the power of chemical composition as a tool to reconstruct the past history of protostars.

  20. Rotating Bullets from A Variable Protostar

    NASA Astrophysics Data System (ADS)

    Chen, Xuepeng; Arce, Héctor G.; Zhang, Qizhou; Launhardt, Ralf; Henning, Thomas

    2016-06-01

    We present Submillimeter Array (SMA) CO (2–1) observations toward the protostellar jet driven by SVS 13 A, a variable protostar in the NGC 1333 star-forming region. The SMA CO (2–1) images show an extremely high-velocity jet composed of a series of molecular “bullets.” Based on the SMA CO observations, we discover clear and large systematic velocity gradients, perpendicular to the jet axis, in the blueshifted and redshifted bullets. After discussing several alternative interpretations, such as twin-jets, jet precession, warped disk, and internal helical shock, we suggest that the systematic velocity gradients observed in the bullets result from the rotation of the SVS 13 A jet. From the SMA CO images, the measured rotation velocities are 11.7–13.7 km s‑1 for the blueshifted bullet and 4.7 ± 0.5 km s‑1 for the redshifted bullet. The estimated specific angular momenta of the two bullets are comparable to those of dense cores, about 10 times larger than those of protostellar envelopes, and about 20 times larger than those of circumstellar disks. If the velocity gradients are due to the rotation of the SVS 13 A jet, the significant amount of specific angular momenta of the bullets indicates that the rotation of jets/outflows is a key mechanism to resolve the so-called “angular momentum problem” in the field of star formation. The kinematics of the bullets suggests that the jet launching footprint on the disk has a radius of ∼7.2–7.7 au, which appears to support the extended disk-wind model. We note that further observations are needed to comprehensively understand the kinematics of the SVS 13 A jet, in order to confirm the rotation nature of the bullets.

  1. HST/WFC3 imaging of protostellar jets in Carina: [Fe II] emission tracing massive jets from intermediate-mass protostars

    NASA Astrophysics Data System (ADS)

    Reiter, Megan; Smith, Nathan

    2013-08-01

    We present narrow-band Wide Field Camera 3 (WFC3)-UVIS and WFC3-IR images of four externally irradiated protostellar jets in the Carina nebula: HH 666, HH 901, HH 902 and HH 1066. These massive jets are unusual because they are bathed in UV radiation from dozens of nearby O-type stars, but despite the strong incident ionizing radiation, portions of the jet remain neutral. Near-IR [Fe II] images reveal dense, neutral gas that was not seen in previous studies of Hα emission. We show that near-IR [Fe II] emitting gas must be self-shielded from Lyman continuum photons, regardless of its excitation mechanism (shocks, far-ultraviolet radiation or both). High densities are required for the survival of Fe+ amid the strong Lyman continuum luminosity from Tr14, raising estimates of the mass-loss rates by an order of magnitude. Higher jet mass-loss rates require higher accretion rates on to their driving protostars, implying that these jets are driven by intermediate-mass (˜2-8 M⊙) stars. Indeed, the IR driving sources of two of these outflows have luminosities that require intermediate-mass protostars (the other two are so deeply embedded that their luminosity is uncertain). All four of these HH jets are highly collimated, with opening angles of only a few degrees, similar to those observed in low-mass protostars. We propose that these jets reflect essentially the same outflow phenomenon seen in wide-angle molecular outflows associated with intermediate- and high-mass protostars, but that the collimated atomic jet core is irradiated and rendered observable in the harsh radiative environment of the Carina nebula. In more quiescent environments, this atomic core remains invisible, and outflows traced by shock-excited molecules in the outflow cavity give the impression that these outflows have a wider opening angle. Thus, the externally irradiated jets in Carina constitute a new view of collimated jets from intermediate-mass protostars and offer strong additional evidence

  2. Luminosity functions for very low mass stars and brown dwarfs

    NASA Technical Reports Server (NTRS)

    Laughlin, Gregory; Bodenheimer, Peter

    1993-01-01

    A theoretical investigation of the luminosity function for low-mass objects to constrain the stellar initial mass function at the low-mass end is reported. The ways in which luminosity functions for low-mass stars are affected by star formation histories, brown dwarf and premain-sequence cooling rates and main-sequence mass luminosity relations, and the IMF are examined. Cooling rates and the mass-luminosity relation are determined through a new series of evolutionary calculations for very low mass stars and brown dwarfs in the range 0.05-0.50 solar mass. Model luminosity functions are constructed for specific comparison with the results of four recent observational surveys. The likelihood that the stellar mass function in the solar neighborhood is increasing at masses near the bottom of the main sequence and perhaps at lower masses is confirmed. In the most optimistic case, brown dwarfs contribute half of the local missing disk mass. The actual contribution is likely to be considerably less.

  3. Low-Mass, Low-Power Hall Thruster System

    NASA Technical Reports Server (NTRS)

    Pote, Bruce

    2015-01-01

    NASA is developing an electric propulsion system capable of producing 20 mN thrust with input power up to 1,000 W and specific impulse ranging from 1,600 to 3,500 seconds. The key technical challenge is the target mass of 1 kg for the thruster and 2 kg for the power processing unit (PPU). In Phase I, Busek Company, Inc., developed an overall subsystem design for the thruster/cathode, PPU, and xenon feed system. This project demonstrated the feasibility of a low-mass power processing architecture that replaces four of the DC-DC converters of a typical PPU with a single multifunctional converter and a low-mass Hall thruster design employing permanent magnets. In Phase II, the team developed an engineering prototype model of its low-mass BHT-600 Hall thruster system, with the primary focus on the low-mass PPU and thruster. The goal was to develop an electric propulsion thruster with the appropriate specific impulse and propellant throughput to enable radioisotope electric propulsion (REP). This is important because REP offers the benefits of nuclear electric propulsion without the need for an excessively large spacecraft and power system.

  4. LOW-MASS STAR FORMATION TRIGGERED BY EARLY SUPERNOVA EXPLOSIONS

    SciTech Connect

    Chiaki, Gen; Yoshida, Naoki; Kitayama, Tetsu

    2013-01-01

    We study the formation of low-mass and extremely metal-poor stars in the early universe. Our study is motivated by the recent discovery of a low-mass (M {sub *} {<=} 0.8 M {sub Sun }) and extremely metal-poor (Z {<=} 4.5 Multiplication-Sign 10{sup -5} Z {sub Sun }) star in the Galactic halo by Caffau et al. We propose a model that early supernova (SN) explosions trigger the formation of low-mass stars via shell fragmentation. We first perform one-dimensional hydrodynamic simulations of the evolution of an early SN remnant. We show that the shocked shell undergoes efficient radiative cooling and then becomes gravitationally unstable to fragment and collapse in about a million years. We then follow the thermal evolution of the collapsing fragments using a one-zone code. Our one-zone calculation treats chemistry and radiative cooling self-consistently in low-metallicity gas. The collapsing gas cloud evolves roughly isothermally, until it cools rapidly by dust continuum emission at the density 10{sup 13}-10{sup 14} cm{sup -3}. The cloud core then becomes unstable and fragments again. We argue that early SNe can trigger the formation of low-mass stars in the extremely metal-poor environment as Caffau et al. discovered recently.

  5. Enhancement of low-mass dileptons in heavy ion collisions

    SciTech Connect

    Li, G.Q.; Ko, C.M.; Brown, G.E. |

    1995-11-27

    Using a relativistic transport model for the expansion stage of S+Au collisions at 200 GeV/nucleon, we show that the recently observed enhancement of low-mass dileptons by the CERES Collaboration can be explained by the decrease of vector meson masses in hot and dense hadronic matter. {copyright} {ital 1995} {ital The} {ital American} {ital Physical} {ital Society}.

  6. Resolving the Discrepancy of Low-Mass Stars with IGRINS

    NASA Astrophysics Data System (ADS)

    Riddle, Andrew; Kraus, Adam L.

    2015-01-01

    Observed properties of low-mass stars (M < 0.8 solar msses) have been found to be in disagreement with stellar models, the observed radii being inflated and the observed temperatures being too low. To study this discrepancy, we are observing a sample of low-mass eclipsing binaries using the 2.7-m Harlan J. Smith telescope at McDonald Observatory as well as the LCOGT network to increase the number of well-characterized systems. We are also using IGRINS, a new high resolution (R=40,000) IR (H+K) spectrograph on the 2.7-m HJST, to measure the fundamental stellar parameters (Teff, R, M, abundances, activity) of a sample of eclipsing binaries consisting of two low-mass components. Finally, to calibrate these eclipsing binaries, we are observing a temperature calibration sample of single M dwarfs with precise temperature measurements from interferometry and a metallicity calibration sample of M dwarfs in wide binaries with solar-type stars. Relationships between these parameters will help us better understand the discrepancy between models and observed properties of low-mass stars.

  7. HOT WATER IN THE INNER 100 AU OF THE CLASS 0 PROTOSTAR NGC 1333 IRAS2A

    SciTech Connect

    Visser, Ruud; Bergin, Edwin A.; Jorgensen, Jes K.; Kristensen, Lars E.; Van Dishoeck, Ewine F.

    2013-05-20

    Evaporation of water ice above 100 K in the inner few 100 AU of low-mass embedded protostars (the so-called hot core) should produce quiescent water vapor abundances of {approx}10{sup -4} relative to H{sub 2}. Observational evidence so far points at abundances of only a few 10{sup -6}. However, these values are based on spherical models, which are known from interferometric studies to be inaccurate on the relevant spatial scales. Are hot cores really that much drier than expected, or are the low abundances an artifact of the inaccurate physical models? We present deep velocity-resolved Herschel-HIFI spectra of the 3{sub 12}-3{sub 03} lines of H{sub 2}{sup 16}O and H{sub 2}{sup 18}O (1097 GHz, E{sub u}/k = 249 K) in the low-mass Class 0 protostar NGC 1333 IRAS2A. A spherical radiative transfer model with a power-law density profile is unable to reproduce both the HIFI data and existing interferometric data on the H{sub 2}{sup 18}O 3{sub 13}-2{sub 20} line (203 GHz, E{sub u}/k = 204 K). Instead, the HIFI spectra likely show optically thick emission from a hot core with a radius of about 100 AU. The mass of the hot core is estimated from the C{sup 18}O J = 9-8 and 10-9 lines. We derive a lower limit to the hot water abundance of 2 Multiplication-Sign 10{sup -5}, consistent with the theoretical predictions of {approx}10{sup -4}. The revised HDO/H{sub 2}O abundance ratio is 1 Multiplication-Sign 10{sup -3}, an order of magnitude lower than previously estimated.

  8. COUNTING LOW-MASS STARS IN INTEGRATED LIGHT

    SciTech Connect

    Conroy, Charlie; Van Dokkum, Pieter

    2012-03-01

    Low-mass stars (M {approx}< 0.4 M{sub Sun }) are thought to comprise the bulk of the stellar mass of galaxies but they constitute only of order 1 percent of the bolometric luminosity of an old stellar population. Directly estimating the number of low-mass stars from integrated flux measurements of old stellar systems is therefore possible but very challenging, given the numerous variables that can affect the light at the percent level. Here we present a new population synthesis model created specifically for the purpose of measuring the low-mass initial mass function (IMF) down to {approx}0.1 M{sub Sun} for metal-rich stellar populations with ages in the range 3-13.5 Gyr. Our fiducial model is based on the synthesis of three separate isochrones, and a combination of optical and near-IR empirical stellar libraries in order to produce integrated light spectra over the wavelength interval 0.35 {mu}m < {lambda} < 2.4 {mu}m at a resolving power of R Almost-Equal-To 2000. New synthetic stellar atmospheres and spectra have been computed in order to model the spectral variations due to changes in individual elemental abundances including C, N, Na, Mg, Si, Ca, Ti, Fe, and generic {alpha} elements. We demonstrate the power of combining blue spectral features with surface gravity-sensitive near-IR features in order to simultaneously constrain the low-mass IMF, stellar population age, metallicity, and abundance pattern from integrated light measurements. Finally, we show that the shape of the low-mass IMF can also be directly constrained by employing a suite of surface gravity-sensitive spectral features, each of which is most sensitive to a particular mass interval.

  9. Bipolar Molecular Outflows from High-Mass Protostars

    NASA Astrophysics Data System (ADS)

    Su, Yu-Nung; Zhang, Qizhou; Lim, Jeremy

    2004-03-01

    We report observations of the bipolar molecular outflows associated with the luminous (~2×104 Lsolar) far-IR sources IRAS 21519+5613 and IRAS 22506+5944, as well the dust and molecular gas condensations on which these outflows appear to be centered. The observations were made in 12CO, 13CO, C18O, and continuum at 3 mm with the BIMA array and in 12CO and 13CO with the NRAO 12 m telescope to recover extended emission filtered out by the interferometric array. We find that the outflow associated with each IRAS source shows a clear bipolar morphology in 12CO, with properties (i.e., total mass of order 10-100 Msolar, mass-outflow rate >~10-3 Msolar, dynamical timescale 104-105 yr, and energetics) comparable with those of other massive outflows associated with luminous young stellar objects. Each outflow appears to be centered on a dust and gas condensation with a mass of 200-300 Msolar, likely marking the location of the driving source. The outflow lobes of both sources are fully resolved along their major but not minor axes, and they have collimation factors that may be comparable with young low-mass stars. The mass-velocity diagrams of both outflows change in slope at a velocity of ~10 km s-1, suggesting that the high-velocity component (HVC) may drive the low-velocity component (LVC). Although the HVC of IRAS 21519+5613 shows evidence for deceleration, no such signature is seen in the HVC of IRAS 22506+5944. Neither HVC has a momentum supply rate sufficient to drive their corresponding LVCs, although it is possible that the HVC is more highly excited and hence its thrust underestimated. Like for other molecular outflows the primary driving agent cannot be ionized gas, leaving atomic gas as the other remaining candidate. Neither IRAS 21519+5613 nor IRAS 22506+5944 exhibits detectable free-free emission, which together with the observed properties of their molecular outflows and surrounding condensations make them credible candidates for high-mass protostars. The mass

  10. Observations of water with Herschel/HIFI toward the high-mass protostar AFGL 2591

    NASA Astrophysics Data System (ADS)

    Choi, Y.; van der Tak, F. F. S.; van Dishoeck, E. F.; Herpin, F.; Wyrowski, F.

    2015-04-01

    Context. Water is an important chemical species in the process of star formation, and a sensitive tracer of physical conditions in star-forming regions because of its rich line spectrum and large abundance variations between hot and cold regions. Aims: We use spectrally resolved observations of rotational lines of H2O and its isotopologs to constrain the physical conditions of the water emitting region toward the high-mass protostar AFGL 2591. Methods: Herschel/HIFI spectra from 552 up to 1669 GHz show emission and absorption in 14 lines of H 2 O, H218O, and H217O. We decompose the line profiles into contributions from the protostellar envelope, the bipolar outflow, and a foreground cloud. We use analytical estimates and rotation diagrams to estimate excitation temperatures and column densities of H2O in these components. Furthermore, we use the non-local thermodynamic equilibrium (LTE) radiative transfer code RADEX to estimate the temperature and volume density of the H2O emitting gas. Results: Assuming LTE, we estimate an excitation temperature of ~42 K and a column density of ~2 × 1014 cm-2 for the envelope and ~45 K and 4 × 1013 cm-2 for the outflow, in beams of 4″ and 30″, respectively. Non-LTE models indicate a kinetic temperature of ~60-230 K and a volume density of 7 × 106-108 cm-3 for the envelope, and a kinetic temperature of ~70-90 K and a gas density of ~107-108 cm-3 for the outflow. The ortho/para ratio of the narrow cold foreground absorption is lower than three (~1.9 ± 0.4), suggesting a low temperature. In contrast, the ortho/para ratio seen in absorption by the outflow is about 3.5 ± 1.0, as expected for warm gas. Conclusions: The water abundance in the outer envelope of AFGL 2591 is ~10-9 for a source size of 4″, similar to the low values found for other high-mass and low-mass protostars, suggesting that this abundance is constant during the embedded phase of high-mass star formation. The water abundance in the outflow is ~10-10 for a

  11. The Formation and Evolution of Young Low-mass Stars within Halos with High Concentration of Dark Matter Particles

    NASA Astrophysics Data System (ADS)

    Casanellas, Jordi; Lopes, IlíDio

    2009-11-01

    The formation and evolution of low-mass stars within dense halos of dark matter (DM) leads to evolution scenarios quite different from the classical stellar evolution. As a result of our detailed numerical work, we describe these new scenarios for a range of DM densities on the host halo, for a range of scattering cross sections of the DM particles considered, and for stellar masses from 0.7 to 3 M sun. For the first time, we also computed the evolution of young low-mass stars in their Hayashi track in the pre-main-sequence phase and found that, for high DM densities, these stars stop their gravitational collapse before reaching the main sequence, in agreement with similar studies on first stars. Such stars remain indefinitely in an equilibrium state with lower effective temperatures (|ΔT eff|>103 K for a star of one solar mass), the annihilation of captured DM particles in their core being the only source of energy. In the case of lower DM densities, these protostars continue their collapse and progress through the main-sequence burning hydrogen at a lower rate. A star of 1 M sun will spend a time period greater than the current age of the universe consuming all the hydrogen in its core if it evolves in a halo with DM density ρχ = 109 GeV cm-3. We also show the strong dependence of the effective temperature and luminosity of these stars on the characteristics of the DM particles and how this can be used as an alternative method for DM research.

  12. ISO Detection of CO(+) toward the protostar IRAS 16293-2422

    NASA Astrophysics Data System (ADS)

    Ceccarelli, C.; Caux, E.; Wolfire, M.; Rudolph, A.; Nisini, B.; Saraceno, P.; White, G. J.

    1998-03-01

    In this letter we report the detection of eight high-N rotational transitions of CO(+) towards a low mass protostar, IRAS 16293-2422. The source was observed with the Long Wavelength Spectrometer on board the Infrared Space Observatory. This is the first time that CO(+) has been detected in a low luminosity source and the first time that high-N lines have been detected in any source. The detection of these lines was not predicted by models and consequently, their interpretation is a challenge. We discuss the possibility that the observed CO(+) emission originates in the dense inner regions illuminated by the UV field created in the accretion shock (formed by infalling material), and conclude that this is an improbable explanation. We have also considered the possibility that a strong, dissociative J-shock at ~ 500 AU from the star is the origin of the CO(+) emission. This model predicts CO(+) column densities in rough agreement with the observations if the magnetic field is ~ 1 mG and the shock velocity is 100 km s(-1) . Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) with the participation of ISAS and NASA.

  13. ISO Detection of CO(+) toward the Protostar IRAS 16293-2422

    NASA Astrophysics Data System (ADS)

    Rudolph, A.; Ceccarelli, C.; Caux, E.; Wolfire, M.; Nisini, B.; Saraceno, P.; White, G. J.

    1997-12-01

    We report the detection of eight high-N rotational transitions of CO(+) towards a low mass protostar, IRAS 16293-2422. The source was observed with the Long Wavelength Spectrometer on board the Infrared Space Observatory. This is the first time that CO(+) has been detected in a low luminosity source and the first time that high-N lines have been detected in any source. The detection of these lines is totally unpredicted by models and, consequently, their interpretation is a challenge. We discuss the possibility that the observed CO(+) emission originates in the dense inner regions illuminated by the UV field created in the accretion shock (formed by the infalling material), and conclude that this is an improbable explanation. We have also considered the possibility that a strong, dissociative J-shock at ~ 500 AU from the star is the origin of the CO(+) emission. This model predicts CO(+) column densities in rough agreement with the observations if the magnetic field is ~ 1 mG and the shock velocity is 100 km s(-1) .

  14. PROTOSTARS AND STARS IN THE CORONET CLUSTER: AGE, EVOLUTION, AND CLUSTER STRUCTURE

    SciTech Connect

    Sicilia-Aguilar, Aurora; Henning, Thomas; Kainulainen, Jouni; Roccatagliata, Veronica

    2011-08-01

    We present new optical spectroscopy with the FLAMES spectrograph at the Very Large Telescope (VLT), near-IR imaging with VLT/HAWK-I, and 870 {mu}m mapping with APEX/LABOCA of the Coronet cluster. The optical data allow us to estimate spectral types, extinction, and the presence of accretion in 6 more M-type members, in addition to the 12 that we had previously studied. The submillimeter maps and near-IR data reveal the presence of nebular structures and high extinction regions, which are in some cases associated to known IR, optical, and X-ray sources. Most star formation is associated to two elongated structures crossing in the central part of the cluster. Placing all the 18 objects with known spectral types and extinction in an H-R diagram suggests that the cluster is younger than previously thought (<2 Myr, and probably {approx}0.5-1 Myr). The new age estimate is in agreement with the evolutionary status of the various protostars in the region and with its compactness (<1.3 pc across), but results in a conflict with the low disk and accretion fraction (only 50%-65% of low-mass stars appear to have protoplanetary disks, and most transitional and homologously depleted disks are consistent with no accretion) and with the evolutionary features observed in the mid-IR spectra and spectral energy distributions of the disks.

  15. Mosquitoes survive raindrop collisions by virtue of their low mass

    PubMed Central

    Dickerson, Andrew K.; Shankles, Peter G.; Madhavan, Nihar M.; Hu, David L.

    2012-01-01

    In the study of insect flight, adaptations to complex flight conditions such as wind and rain are poorly understood. Mosquitoes thrive in areas of high humidity and rainfall, in which raindrops can weigh more than 50 times a mosquito. In this combined experimental and theoretical study, we here show that free-flying mosquitoes can survive the high-speed impact of falling raindrops. High-speed videography of those impacts reveals a mechanism for survival: A mosquito’s strong exoskeleton and low mass renders it impervious to falling drops. The mosquito’s low mass causes raindrops to lose little momentum upon impact and so impart correspondingly low forces to the mosquitoes. Our findings demonstrate that small fliers are robust to in-flight perturbations. PMID:22665779

  16. Low Mass Muscle Actuators (LoMMAs) Using Electroactive Polymers

    NASA Technical Reports Server (NTRS)

    Bar-Cohen, Y.; Xue, T.; Joffe, B.; Lih, S. S.; Willis, P.; Simpson, J.; Smith, J.; Clair, T.; Shahinpoor, M.

    1997-01-01

    NASA is using actuation devices for many space applications and there is an increasing need to cut their cost as well as reduce their size, mass, and power consumption. Existing transducing actuators, such as piezoceramics, are inducing limited displacement levels. Potentially, electroactive polymers (so called EAP) can be formed as inexpensive, low-mass, low-power, miniature muscle actuators that are superior to the widely used actuators.

  17. Low Mass Star Formation in the Norma Cloud

    NASA Astrophysics Data System (ADS)

    Reipurth, B.; Nielbock, M.

    2008-12-01

    A small filamentary cloud in Norma hosts a number of young low-mass stars in various stages of evolution, from visible Hα emission stars to embedded sources detected only in the sub-millimeter regime. The best known source is V346 Nor, an FU Orionis star that brightened in the early 1980s. The morphology of the cloud complex and an apparent age gradient along the cloud suggests that star formation in this region was triggered by an external event.

  18. The different baryonic Tully-Fisher relations at low masses

    NASA Astrophysics Data System (ADS)

    Brook, Chris B.; Santos-Santos, Isabel; Stinson, Greg

    2016-06-01

    We compare the Baryonic Tully-Fisher relation (BTFR) of simulations and observations of galaxies ranging from dwarfs to spirals, using various measures of rotational velocity Vrot. We explore the BTFR when measuring Vrot at the flat part of the rotation curve, Vflat, at the extent of H I gas, Vlast, and using 20 per cent (W20) and 50 per cent (W50) of the width of H I line profiles. We also compare with the maximum circular velocity of the parent halo, V_max^DM, within dark matter only simulations. The different BTFRs increasingly diverge as galaxy mass decreases. Using Vlast one obtains a power law over four orders of magnitude in baryonic mass, with slope similar to the observed BTFR. Measuring Vflat gives similar results as Vlast when galaxies with rising rotation curves are excluded. However, higher rotation velocities would be found for low-mass galaxies if the cold gas extended far enough for Vrot to reach a maximum. W20 gives a similar slope as Vlast but with slightly lower values of Vrot for low-mass galaxies, although this may depend on the extent of the gas in your galaxy sample. W50 bends away from these other relations towards low velocities at low masses. By contrast, V_max^DM bends towards high velocities for low-mass galaxies, as cold gas does not extend out to the radius at which haloes reach V_max^DM. Our study highlights the need for careful comparisons between observations and models: one needs to be consistent about the particular method of measuring Vrot, and precise about the radius at which velocities are measured.

  19. On the origin of the IMF: First detection of a low-mass star ejected from a triple stellar system

    NASA Astrophysics Data System (ADS)

    Loinard, L.; Rodriguez, L. F.; Rodriguez, M.

    2002-12-01

    Using high-resolution, multi-epoch VLA observations, we have detected orbital motions in several low-luminosity protobinary systems in the Taurus and rho-Ophiuchus molecular complexes. The masses obtained from Kepler's third law are of the order of 0.5 to 1 Msun, as would have been expected for such low-mass protostars. In addition, in one of the sources studied (a triple system in Taurus), one of the three component appears to have been recently ejected from the system. During the first 15 of the 20 years covered by the observations, this component has been on a closed elliptical orbit with a velocity of a few km/s, but in the last 5 years, it has started to spiral out at high speed (20 km/s). Such an ejection is not unexpected in a triple system, because such systems are thought to exhibit chaotic behaviours. However, this is the first time that it is detected directly. The implications for the IMF will be discussed

  20. Dwarfing Genes Rht-B1b and Rht-D1b Are Associated with Both Type I FHB Susceptibility and Low Anther Extrusion in Two Bread Wheat Populations.

    PubMed

    He, Xinyao; Singh, Pawan K; Dreisigacker, Susanne; Singh, Sukhwinder; Lillemo, Morten; Duveiller, Etienne

    2016-01-01

    It has been well documented that dwarfing genes Rht-B1b and Rht-D1b are associated with Type I susceptibility to Fusarium head blight (FHB) in wheat; but the underlying mechanism has not been well delineated. Anther extrusion (AE) has also been related to Type I resistance for initial FHB infection, where high AE renders FHB resistance. In this study, two doubled haploid populations were used to investigate the impact of the two dwarfing genes on FHB resistance and AE, and to elucidate the role of AE in Rht-mediated FHB susceptibility. Both populations were derived by crossing the FHB susceptible cultivar 'Ocoroni F86' (Rht-B1a/Rht-D1b) with an FHB resistant variety (Rht-B1b/Rht-D1a), which was 'TRAP#1/BOW//Taigu derivative' in one population (the TO population) and 'Ivan/Soru#2' in the other (the IO population). Field experiments were carried out from 2010 to 2012 in El Batán, Mexico, where spray inoculation was adopted and FHB index, plant height (PH), and AE were evaluated, with the latter two traits showing always significantly negative correlations with FHB severity. The populations were genotyped with the DArTseq GBS platform, the two dwarfing genes and a few SSRs for QTL analysis, and the results indicated that Rht-B1b and Rht-D1b collectively accounted for 0-41% of FHB susceptibility and 13-23% of reduced AE. It was also observed that three out of the four AE QTL in the TO population and four out of the five AE QTL in the IO population were associated with FHB resistance. Collectively, our results demonstrated the effects of Rht-B1b and Rht-D1b on Type I FHB susceptibility and reducing AE, and proposed that their impacts on Type I FHB susceptibility may partly be explained by their effects on reducing AE. The implication of the relationship between the two dwarfing genes and AE for hybrid wheat breeding was also discussed. PMID:27606928

  1. Angular Momentum Evolution in Young Low Mass Stars

    NASA Astrophysics Data System (ADS)

    Pinzón, G.; de La Reza, R.

    2006-06-01

    During the last decades, the study of rotation in young low mass stars has been one of the more active areas in the field of stellar evolution. Many theoretical efforts have been made to understand the angular momentum evolution and our picture now, reveals the main role of the stellar magnetic field in all pre-main sequence stage (Ghosh & Lamb 1979, ApJ, 234, 296; Cameron & Campbell 1993, A&A, 274, 309; Cameron & Campbell 1995, A&A, 298, 133; Kúker, Henning, & Rúdiger 2003, ApJ, 589, 397; Matt & Pudritz 2005, MNRAS, 356, 167). The mean rotation of most of the cool low mass stars remains roughly constant during the T Tauri stage. This can be explained by the disc locking scenario. This paradigm suggest that star start out as CTTS with periods of 4-14 days, perhaps locked to their disc, and that this disc is eventually lost mainly by accretion. At the current time, it is not clear that this is true for all low mass stars. Some authors have questioned its validity for stars less massive than 0.5 solar masses. Although the reality may eventually turn out to be considerably more complex, a simple consideration of the effects of and limits on disc locking of young low mass stars seems necessary.We have investigated the exchange of angular momentum between a low mass star and an accretion disc during the Hayashi Track (Pinzón, Kúker, & de la Reza 2005, in preparation) and also along the first 100Myr of stellar evolution. The model incorporates changes in the star's moment of inertia, magnetic field strength (Elstner & Rúdiger 2000, A&A, 358, 612), angular momentum loss by a magnetic wind and an exponential decrease of the accretion rate. The lifetime of the accretion disc is a free parameter in our model. The resulting rotation rates are in agreement with observed vsin and photometric periods for young stars belonging to co-moving groups and open young clusters.

  2. The First Stars: A Low-Mass Formation Mode

    NASA Technical Reports Server (NTRS)

    Stacy, Athena; Bromm, Volker

    2014-01-01

    We perform numerical simulations of the growth of a Population III stellar system under photodissociating feedback. We start from cosmological initial conditions at z = 100, self-consistently following the formation of a minihalo at z = 15 and the subsequent collapse of its central gas to high densities. The simulations resolve scales as small as approx. 1 AU, corresponding to gas densities of 10(exp 16)/cu cm. Using sink particles to represent the growing protostars, we evolve the stellar system for the next 5000 yr. We find that this emerging stellar group accretes at an unusually low rate compared with minihalos which form at earlier times (z = 20-30), or with lower baryonic angular momentum. The stars in this unusual system will likely reach masses ranging from <1Stellar Mass to approx. 5 Stellar Mass by the end of their main-sequence lifetimes, placing them in the mass range for which stars will undergo an asymptotic giant branch (AGB) phase. Based upon the simulation, we predict the rare existence of Population III stars that have survived to the present day and have been enriched by mass overflow from a previous AGB companion.

  3. The thermal structure of low-mass cloud cores

    NASA Astrophysics Data System (ADS)

    Launhardt, Ralf; Stutz, Amelia; Schmiedecke, Anika; Henning, Thomas; Krause, Oliver; Balog, Zoltan; Beuther, Henrik; Kainulainen, Jouni; Linz, Hendrik; Lippok, Nils; Nielbock, Markus; Ragan, Sarah; Schmalzl, Markus; Shirley, Yancy; Steinacker, Juergen

    2013-07-01

    The evolution of the temperature and density structure of star-forming cloud cores is one of the key aspects in protostellar collapse models. Yet this structure, in particular the temperature, is not well-constrained observationally. In the framework of the EPoS Herschel key project, we observed the NIR extinction and FIR through mm dust emission from selected isolated nearby starless and protostellar cloud cores. Based on these data, we reconstruct the full dust temperature and density structure of the cores. We find that the thermal structure of all globules is completely dominated by external heating through the ISRF and moderate shielding by thin extended halos. All globules have warm outer envelopes (14-20 K) and colder dense interiors (7-11 K) with column densities of up to 10^23 cm^-2 and central volume densities of a few 10^5 cm^-3 (starless cores). The protostars embedded in some of the globules raise the local temperature of the dense cores only within radii out to about 5000 AU, but do not significantly affect the overall thermal balance of the globules.

  4. The first stars: A low-mass formation mode

    SciTech Connect

    Stacy, Athena; Bromm, Volker

    2014-04-10

    We perform numerical simulations of the growth of a Population III stellar system under photodissociating feedback. We start from cosmological initial conditions at z = 100, self-consistently following the formation of a minihalo at z = 15 and the subsequent collapse of its central gas to high densities. The simulations resolve scales as small as ∼1 AU, corresponding to gas densities of 10{sup 16} cm{sup –3}. Using sink particles to represent the growing protostars, we evolve the stellar system for the next 5000 yr. We find that this emerging stellar group accretes at an unusually low rate compared with minihalos which form at earlier times (z = 20-30), or with lower baryonic angular momentum. The stars in this unusual system will likely reach masses ranging from <1 M {sub ☉} to ∼5 M {sub ☉} by the end of their main-sequence lifetimes, placing them in the mass range for which stars will undergo an asymptotic giant branch (AGB) phase. Based upon the simulation, we predict the rare existence of Population III stars that have survived to the present day and have been enriched by mass overflow from a previous AGB companion.

  5. A novel spectral resolution and simultaneous determination of multicomponent mixture of Vitamins B1, B6, B12, Benfotiamine and Diclofenac in tablets and capsules by derivative and MCR-ALS

    NASA Astrophysics Data System (ADS)

    Hegazy, Maha A.; Abdelwahab, Nada S.; Fayed, Ahmed S.

    2015-04-01

    A novel method was developed for spectral resolution and further determination of five-component mixture including Vitamin B complex (B1, B6, B12 and Benfotiamine) along with the commonly co-formulated Diclofenac. The method is simple, sensitive, precise and could efficiently determine the five components by a complementary application of two different techniques. The first is univariate second derivative method that was successfully applied for determination of Vitamin B12. The second is Multivariate Curve Resolution using the Alternating Least Squares method (MCR-ALS) by which an efficient resolution and quantitation of the quaternary spectrally overlapped Vitamin B1, Vitamin B6, Benfotiamine and Diclofenac sodium were achieved. The effect of different constraints was studied and the correlation between the true spectra and the estimated spectral profiles were found to be 0.9998, 0.9983, 0.9993 and 0.9933 for B1, B6, Benfotiamine and Diclofenac, respectively. All components were successfully determined in tablets and capsules and the results were compared to HPLC methods and they were found to be statistically non-significant.

  6. An ultra-high-performance liquid chromatography-tandem mass spectrometry method for simultaneous determination of aflatoxins B1, B2, G1, G2, M1 and M2 in traditional Chinese medicines.

    PubMed

    Han, Zheng; Zheng, Yunliang; Luan, Lianjun; Cai, Zengxuan; Ren, Yiping; Wu, Yongjiang

    2010-04-01

    An ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method for simultaneous determination of aflatoxins B1, B2, G1, G2, M1 and M2 in traditional Chinese medicines (TCMs) was developed. The approach was characterized in details and a special focus was placed on the recovery rates of isolation procedure in different TCM matrices, i.e. rhizomes and roots, seeds, flowers, grasses and leaves. For this purpose, [(13)C(17)]-aflatoxinB1 was employed as the internal standard and a reliable solid phase extraction-based clean-up method was developed. The observed recovery rates of the six aflatoxins ranged from 85.6% to 117.6% in different matrices. Then, the established method was successfully applied to the determination of the six aflatoxins in various TCMs. For 30 commercial samples analyzed, 16 were contaminated with aflatoxins. The mean levels (incidence) of aflatoxins B1, B2, G1 and G2 in positive samples were 1.40 (68.8%), 1.27 (50.0%), 0.50 (43.8%) and 0.94 (43.8%) microg kg(-1), respectively. Interestingly, aflatoxin M1 was detected in two samples with the maximal content of 0.70 microg kg(-1). No sample was contaminated with aflatoxin M2. Meanwhile, a possible association between the contamination levels and the selected herbs was clarified in the present study. PMID:20363399

  7. Simultaneous Determination of Total Vitamins B1, B2, B3, and B6 in Infant Formula and Related Nutritionals by Enzymatic Digestion and LC-MS/MS: Single-Laboratory Validation, First Action 2015.14.

    PubMed

    Salvati, Louis M; McClure, Sean C; Reddy, Todime M; Cellar, Nicholas A

    2016-05-01

    This method provides simultaneous determination of total vitamins B1, B2, B3, and B6 in infant formula and related nutritionals (adult and infant). The method was given First Action for vitamins B1, B2, and B6, but not B3, during the AOAC Annual Meeting in September 2015. The method uses acid phosphatase to dephosphorylate the phosphorylated vitamin forms. It then measures thiamine (vitamin B1); riboflavin (vitamin B2); nicotinamide and nicotinic acid (vitamin B3); and pyridoxine, pyridoxal, and pyridoxamine (vitamin B6) from digested sample extract by liquid chromatography-tandem mass spectrometry. A single-laboratory validation was performed on 14 matrixes provided by the AOAC Stakeholder Panel on Infant Formula and Adult Nutritionals (SPIFAN) to demonstrate method effectiveness. The method met requirements of the AOAC SPIFAN Standard Method Performance Requirement for each of the three vitamins, including average over-spike recovery of 99.6 ± 3.5%, average repeatability of 1.5 ± 0.8% relative standard deviation, and average intermediate precision of 3.9 ± 1.3% relative standard deviation. PMID:27297842

  8. First detection of CF+ towards a high-mass protostar

    NASA Astrophysics Data System (ADS)

    Fechtenbaum, S.; Bontemps, S.; Schneider, N.; Csengeri, T.; Duarte-Cabral, A.; Herpin, F.; Lefloch, B.

    2015-02-01

    Aims: We report the first detection of the J = 1-0 (102.6 GHz) rotational lines of CF+ (fluoromethylidynium ion) towards CygX-N63, a young and massive protostar of the Cygnus X region. Methods: This detection occurred as part of an unbiased spectral survey of this object in the 0.8-3 mm range, performed with the IRAM 30 m telescope. The data were analyzed using a local thermodynamical equilibrium model (LTE model) and a population diagram in order to derive the column density. Results: The line velocity (-4 km s-1) and line width (1.6 km s-1) indicate an origin from the collapsing envelope of the protostar. We obtain a CF+ column density of 4 × 1011 cm-2. The CF+ ion is thought to be a good tracer for C+ and assuming a ratio of 10-6 for CF+/C+, we derive a total number of C+ of 1.2 × 1053 within the beam. There is no evidence of carbon ionization caused by an exterior source of UV photons suggesting that the protostar itself is the source of ionization. Ionization from the protostellar photosphere is not efficient enough. In contrast, X-ray ionization from the accretion shock(s) and UV ionization from outflow shocks could provide a large enough ionizing power to explain our CF+ detection. Conclusions: Surprisingly, CF+ has been detected towards a cold, massive protostar with no sign of an external photon dissociation region (PDR), which means that the only possibility is the existence of a significant inner source of C+. This is an important result that opens interesting perspectives to study the early development of ionized regions and to approach the issue of the evolution of the inner regions of collapsing envelopes of massive protostars. The existence of high energy radiations early in the evolution of massive protostars also has important implications for chemical evolution of dense collapsing gas and could trigger peculiar chemistry and early formation of a hot core. Appendices are available in electronic form at http://www.aanda.org

  9. The Low-mass Astrometric Binary LSR 1610-0040

    NASA Astrophysics Data System (ADS)

    Koren, Seth C.; Blake, Cullen H.; Dahn, Conard C.; Harris, Hugh C.

    2016-03-01

    Even though it was discovered more than a decade ago, LSR 1610-0040 remains an enigma. This object has a peculiar spectrum that exhibits some features typically found in L subdwarfs, and others common in the spectra of more massive M dwarf stars. It is also a binary system with a known astrometric orbital solution. Given the available data, it remains a challenge to reconcile the observed properties of the combined light of LSR 1610-0040AB with current theoretical models of low-mass stars and brown dwarfs. We present the results of a joint fit to both astrometric and radial velocity measurements of this unresolved, low-mass binary. We find that the photocentric orbit has a period P=633.0+/- 1.7 days, somewhat longer than previous results, eccentricity of e=0.42+/- 0.03, and we estimate that the semimajor axis of the orbit of the primary is {a}1≈ 0.32 {{AU}}, consistent with previous results. While a complete characterization of the system is limited by our small number of radial velocity measurements, we establish a likely primary mass range of 0.09-0.10 {M}⊙ from photometric and color-magnitude data. For a primary mass in this range, the secondary is constrained to be 0.06-0.075 {M}⊙ , making a negligible contribution to the total I-band luminosity. This effectively rules out the possibility of the secondary being a compact object such as an old, low-mass white dwarf. Based on our analysis, we predict a likely angular separation at apoapsis comparable to the resolution limits of current high-resolution imaging systems. Measuring the angular separation of the A and B components would finally enable a full, unambiguous solution for the masses of the components of this system.

  10. Where are the Low-mass Population III Stars?

    NASA Astrophysics Data System (ADS)

    Ishiyama, Tomoaki; Sudo, Kae; Yokoi, Shingo; Hasegawa, Kenji; Tominaga, Nozomu; Susa, Hajime

    2016-07-01

    We study the number and the distribution of low-mass Population III (Pop III) stars in the Milky Way. In our numerical model, hierarchical formation of dark matter minihalos and Milky-Way-sized halos are followed by a high-resolution cosmological simulation. We model the Pop III formation in H2 cooling minihalos without metal under UV radiation of the Lyman–Werner bands. Assuming a Kroupa initial mass function (IMF) from 0.15 to 1.0 M ⊙ for low-mass Pop III stars, as a working hypothesis, we try to constrain the theoretical models in reverse by current and future observations. We find that the survivors tend to concentrate on the center of halo and subhalos. We also evaluate the observability of Pop III survivors in the Milky Way and dwarf galaxies, and constraints on the number of Pop III survivors per minihalo. The higher latitude fields require lower sample sizes because of the high number density of stars in the galactic disk, the required sample sizes are comparable in the high- and middle-latitude fields by photometrically selecting low-metallicity stars with optimized narrow-band filters, and the required number of dwarf galaxies to find one Pop III survivor is less than 10 at <100 kpc for the tip of red giant stars. Provided that available observations have not detected any survivors, the formation models of low-mass Pop III stars with more than 10 stars per minihalo are already excluded. Furthermore, we discuss the way to constrain the IMF of Pop III stars at a high mass range of ≳10 M ⊙.

  11. The different baryonic Tully–Fisher relations at low masses

    PubMed Central

    Brook, Chris B.; Santos-Santos, Isabel; Stinson, Greg

    2016-01-01

    We compare the Baryonic Tully–Fisher relation (BTFR) of simulations and observations of galaxies ranging from dwarfs to spirals, using various measures of rotational velocity Vrot. We explore the BTFR when measuring Vrot at the flat part of the rotation curve, Vflat, at the extent of H i gas, Vlast, and using 20 per cent (W20) and 50 per cent (W50) of the width of H i line profiles. We also compare with the maximum circular velocity of the parent halo, \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{upgreek} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} }{}$V_{\\rm max}^{\\rm DM}$\\end{document}, within dark matter only simulations. The different BTFRs increasingly diverge as galaxy mass decreases. Using Vlast one obtains a power law over four orders of magnitude in baryonic mass, with slope similar to the observed BTFR. Measuring Vflat gives similar results as Vlast when galaxies with rising rotation curves are excluded. However, higher rotation velocities would be found for low-mass galaxies if the cold gas extended far enough for Vrot to reach a maximum. W20 gives a similar slope as Vlast but with slightly lower values of Vrot for low-mass galaxies, although this may depend on the extent of the gas in your galaxy sample. W50 bends away from these other relations towards low velocities at low masses. By contrast, \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{upgreek} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} }{}$V_{\\rm max}^{\\rm DM}$\\end{document} bends towards high velocities for low-mass galaxies, as cold gas does not extend out to the radius at which haloes reach \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage

  12. The APOGEE Low-Mass Star Ancillary Project

    NASA Astrophysics Data System (ADS)

    Blake, Cullen; Mahadevan, Suvrath; Deshpande, Rohit; Bender, Chad F.; Terrien, Ryan; Crepp, Justin R.; Carlberg, Joleen K.; Nidever, David L.; Stassun, Keivan; Hawley, Suzanne L.; Hearty, Fred; Allende-Prieto, Carlos

    2015-01-01

    As a high-resolution, near-infrared, fiber-fed instrument, APOGEE presents a unique opportunity to obtain multi-epoch radial velocity measurements of a large number of low-mass stars. These observations will reveal unseen companions, improving our understanding of stellar multiplicity at the bottom of the Main Sequence, and may even identify candidate sub-stellar companions. These same data contains an unprecedented wealth of information about the kinematics, rotation, and metallicities of these stars. I will describe the status of our Ancillary Science program, and ongoing efforts to get the best possible radial velocity precision from the APOGEE data.

  13. Discovery of Low Mass Binary with Super Jupiter Companion

    NASA Astrophysics Data System (ADS)

    Anthes Rich, Evan; Wisniewski, John P.; Hashimoto, Jun; Brandt, Timothy; Kuzuhara, Masayuki; Tamura, Motohide

    2015-12-01

    Transit and radial velocity surveys have been prolific in detecting ~2000 confirmed planets to date. While few directly imaged planets have detected, such systems provide a unique scientific opportunity to probe exoplanets at larger angular separation, younger ages, and study their atmospheres. We present new L- and M-band AO observations, obtained with IRCS on Subaru, of a super Jupiter companion orbiting a cool dwarf. We show that the central object is likely a binary, thereby making this system the first likely directly imaged planetary mass companion surrounding a low mass binary system.

  14. Low-Mass Materials and Vertex Detector Systems

    SciTech Connect

    Cooper, William E.

    2014-01-01

    Physics requirements set the material budget and the precision and sta bility necessary in low - mass vertex detector sy s tems . Operational considerations, along with physics requirements , set the operating environment to be provided and determine the heat to be removed. Representative materials for fulfilling those requirements are described and properties of the materials are tabulated. A figure of merit is proposed to aid in material selection. Multi - layer structures are examined as a method to allow material to be used effectively, thereby reducing material contributions. Fin ally, comments are made on future directions to be considered in using present materials effectively and in developing new materials.

  15. Age discrimination among motions of low mass stars.

    NASA Astrophysics Data System (ADS)

    Upgren, A. R.

    Motions of low mass dwarf stars have become much better known than was the case when the concept of the basic solar motion was introduced. The group motions which they define show that older stars have mean motions directed inward towards the galactic center, as well as the well-known mean motion in the direction opposite to that of galactic rotation, when compared to younger stars. This radial motion difference is revealed among stars divided according to their emission intensities as well as kinematical age related parameters.

  16. Outer Atmospheres of Low Mass Stars — Flare Characteristics.

    NASA Astrophysics Data System (ADS)

    Lalitha, S.; Schmitt, J. H. M. M.

    2013-04-01

    We compare the coronal properties during flares on active low mass stars CN Leonis, AB Doradus A and Proxima Centauri observed with XMM-Newton. From the X-ray data we analyze the temporal evolution of temperature, emission measure and coronal abundance. The nature of these flares are with secondary events following the first flare peak in the light curve, raising the question regarding the involved magnetic structure. We infer from the plasma properties and the geometry of the flaring structure that the flare originates from a compact arcade rather than in a single loop.

  17. Probing the water and CO snow lines in the young protostar NGC 1333-IRAS4B

    NASA Astrophysics Data System (ADS)

    Anderl, Sibylle; Maret, Sébastien; André, Philippe; Maury, Anaëlle; Belloche, Arnaud; Cabrit, Sylvie; Codella, Claudio; Lefloch, Bertrand

    2015-08-01

    Today, we believe that the onset of life requires free energy, water, and complex, probably carbon-based chemistry. In the interstellar medium, complex organic molecules seem to mostly form in reactions happening on the icy surface of dust grains, such that they are released into the gas phase when the dust is heated. The resulting “snow lines”, marking regions where ices start to sublimate, play an important role for planet growth and bulk composition in protoplanetary disks. However, they can already be observed in the envelopes of the much younger, low-mass Class 0 protostars that are still in their early phase of heavy accretion. The information on the sublimation regions of different kinds of ices can be used to understand the chemistry of the envelope, its temperature and density structure, and may even hint at the history of the accretion process. Accordingly, it is a crucial piece of information in order to get the full picture of how organic chemistry evolves already at the earliest stages of the formation of sun-like stars. As part of the CALYPSO Large Program (http://irfu.cea.fr/Projets/Calypso/), we have obtained observations of C18O, N2H+ and CH3OH towards the Class 0 protostar NGC 1333-IRAS4B with the IRAM Plateau de Bure interferometer at sub-arcsecond resolution. Of these we use the methanol observations as a proxy for the water snow line, assuming methanol is trapped in water ice. The observed anti-correlation of C18O and N2H+, with N2H+ forming a ring around the centrally peaked C18O emission, reveals for the first time the CO snow line in this protostellar envelope, with a radius of ~300 AU. The methanol emission is much more compact than that of C18O, and traces the water snow line with a radius of ~40 AU. We have modeled the emission using a chemical model coupled with a radiative transfer module. We find that the CO snow line appears further inwards than expected from the binding energy of pure CO ices. This may hint at CO being frozen out

  18. Observational dynamics of low-mass stellar systems

    NASA Astrophysics Data System (ADS)

    Frank, M. J.

    The last fifteen years have seen the discovery of new types of low-mass stellar systems that bridge the gap between the once well-separated regimes of galaxies and of star clusters. Whether such objects are considered galaxies depends also on the definition of the term ``galaxy'', and several possible criteria are based on their internal dynamics (e.g. the common concept that galaxies contain dark matter). Moreover, studying the internal dynamics of low-mass stellar systems may also help understand their origin and evolutionary history. The focus of this paper is on two classes of stellar systems at the interface between star clusters and dwarf galaxies: ultra-compact dwarf galaxies (UCDs) and diffuse Galactic globular clusters (GCs). A review of our current knowledge on the properties of UCDs is provided and dynamical considerations applying to diffuse GCs are introduced. In the following, recent observational results on the internal dynamics of individual UCDs and diffuse Galactic globular clusters are presented. Partly based on observations obtained at the European Southern Observatory, Chile (Observing Programmes 078.B-0496(B) and 081.B-0282). Doctoral Thesis Award Lecture 2013

  19. Doppler disc tomography applied to low-mass AGN spin

    NASA Astrophysics Data System (ADS)

    Middleton, Matthew J.; Ingram, Adam R.

    2015-01-01

    Doppler tomography can provide a powerful means of determining black hole spin when our view to the central regions are revealed and obscured by optically thick orbiting material, and can provide an independent estimate that does not suffer as many degeneracies as traditional methods. For low-mass active galactic nuclei (AGN), time-dependent obscuration is expected to leave a signature in the changing spectrum of the disc emission which extends into the soft X-ray bandpass. We create a spectral model incorporating Doppler tomography and apply it to the case of the low-mass (8 × 105 M⊙) AGN, RX J1301.9+2747 which shows unusual timing properties in the form of short-lived flares that we argue are best explained by the orbit of a window through an optically thick wind. Modelling the phase-resolved spectrum over the course of the highest data quality flare indicates a very low spin even when we relax our constraints. This is the lowest mass AGN for which a spin has been measured and the first via this technique. We note that, as the mass and spin are very low, this appears to favour supermassive black hole (SMBH) growth by chaotic rather than constant accretion.

  20. Angular momentum transport within evolved low-mass stars

    SciTech Connect

    Cantiello, Matteo; Bildsten, Lars; Paxton, Bill; Mankovich, Christopher; Christensen-Dalsgaard, Jørgen

    2014-06-10

    Asteroseismology of 1.0-2.0 M {sub ☉} red giants by the Kepler satellite has enabled the first definitive measurements of interior rotation in both first ascent red giant branch (RGB) stars and those on the helium burning clump. The inferred rotation rates are 10-30 days for the ≈0.2 M {sub ☉} He degenerate cores on the RGB and 30-100 days for the He burning core in a clump star. Using the Modules for Experiments in Stellar Evolution code, we calculate state-of-the-art stellar evolution models of low mass rotating stars from the zero-age main sequence to the cooling white dwarf (WD) stage. We include transport of angular momentum due to rotationally induced instabilities and circulations, as well as magnetic fields in radiative zones (generated by the Tayler-Spruit dynamo). We find that all models fail to predict core rotation as slow as observed on the RGB and during core He burning, implying that an unmodeled angular momentum transport process must be operating on the early RGB of low mass stars. Later evolution of the star from the He burning clump to the cooling WD phase appears to be at nearly constant core angular momentum. We also incorporate the adiabatic pulsation code, ADIPLS, to explicitly highlight this shortfall when applied to a specific Kepler asteroseismic target, KIC8366239.

  1. New Low-Mass Members of Nearby Young Moving Groups

    NASA Astrophysics Data System (ADS)

    Schlieder, Joshua; Simon, Michal; Rice, Emily; Lepine, Sebastien

    2012-08-01

    We are now ready to expand our program to identify new low-mass members of nearby young moving groups (NYMGs) to stars of mass ≤0.3 M_⊙. This is important to: (1) complete the census of low-mass stars near the Sun, (2) provide high priority targets for disk and exoplanet studies by direct imaging, and (3) provide a well- characterized sample of nearby, young stars for detailed study of their physical and kinematic properties. Our proven technique starts with a proper motion selection algorithm, proceeds to vet the sample for indicators of youth, and requires as its last step the measurement of candidate member radial velocities (RVs). So far, we have measured more than 100 candidate RVs using CSHELL on the NASA-IRTF and PHOENIX on Gemini-South, yielding more than 50 likely new moving group members. Here we propose to continue our RV follow-up of candidate NYMG members using PHOENIX on the KPNO 4m. We aim to measure RVs and determine spectral types of 23 faint (V≥15, H≥9), late-type (≥M4) candidates of the (beta) Pic (10 Myrs), AB Dor (70 Myrs), Tuc/Hor (30 Myrs), and TW Hydrae (8 Myrs) moving groups.

  2. Testing the correlation between low mass planets and debris disks

    NASA Astrophysics Data System (ADS)

    Kalas, Paul

    2014-10-01

    The number of dusty debris disks has increased across all spectral types through recent infrared surveys. This has provided greater overlap with stars known to host extrasolar planets via RV surveys. New studies have therefore investigated how the different properties of host stars, exoplanets, and debris disks may be correlated, with the objective of giving empirical support to competing theories of planet formation and evolution. One such emerging correlation is that stars with only low mass planets are more likely to host prominent debris disks than stars that have at least one giant planet. If true, then M dwarfs should have abundant debris disks given that they more frequently have low mass planetary systems. However, the information needed to critically test these ideas is lacking. For most systems, the presence of an outer planet with >30 Earth masses has not been observationally tested, nor are there many M dwarf debris disks available for detailed scrutiny. Here we propose to use STIS coronagraphy to image for the first time the debris disks around three nearby stars in optical scattered light. Searching for sharp dust belt structures indirectly tests for the existence of outer planets that are otherwise undetectable by RV or adaptive optics planet searches. Moreover, two of our target stars are the most recently discovered M dwarf debris disks, both closer to the Sun than AU Mic. The scattered light observations of these two targets would present a major advance in characterizing how M dwarf debris disks co-evolve with planets under different stellar environments.

  3. Exploring The Wide Main Sequence of Low Mass Stars

    NASA Astrophysics Data System (ADS)

    Pewett, Tiffany; Henry, T. J.; Hosey, A. D.; Jao, W.; Lepine, S.; Riedel, A. R.; Winters, J. G.; RECONS Team

    2014-01-01

    The RECONS (REsearch Consortium On Nearby Stars, www.recons.org) team has compiled photometric and astrometric data on over 3000 stars with trigonometric parallaxes placing them within 25 parsecs, allowing for an accurate representation of the H-R Diagram from A stars through M stars. We find that the main sequence is widest, by up to 2.5 full magnitudes in Mv, in the region of low mass K and M dwarf stars. This corresponds to a factor of almost 10 in luminosity among stars of the same temperature, but a detailed understanding of the causes of this range remains elusive. Given that temperature and radius determine the observed luminosity of a star, stars with identical temperatures must have radii differing by up to a factor of three to account for the width of the main sequence. In order to determine the underlying causes of the different radii, we have embarked on a project to measure the variability, rotation, ages, and metallicities of a large sample of the nearest low mass stars. We are comparing these stars to known young stars and cool subdwarfs in the same temperature slices to map the complex interplay of these many factors. Here we present our initial findings from the photometric variability data and first spectroscopic results. This effort is supported by the NSF through grants AST-0908402 and AST-1109445, and via observations made possible by the SMARTS Consortium.

  4. MASS-RADIUS RELATIONSHIPS FOR VERY LOW MASS GASEOUS PLANETS

    SciTech Connect

    Batygin, Konstantin; Stevenson, David J.

    2013-05-20

    Recently, the Kepler spacecraft has detected a sizable aggregate of objects, characterized by giant-planet-like radii and modest levels of stellar irradiation. With the exception of a handful of objects, the physical nature, and specifically the average densities, of these bodies remain unknown. Here, we propose that the detected giant planet radii may partially belong to planets somewhat less massive than Uranus and Neptune. Accordingly, in this work, we seek to identify a physically sound upper limit to planetary radii at low masses and moderate equilibrium temperatures. As a guiding example, we analyze the interior structure of the Neptune-mass planet Kepler-30d and show that it is acutely deficient in heavy elements, especially compared with its solar system counterparts. Subsequently, we perform numerical simulations of planetary thermal evolution and in agreement with previous studies, show that generally, 10-20 M{sub Circled-Plus }, multi-billion year old planets, composed of high density cores and extended H/He envelopes can have radii that firmly reside in the giant planet range. We subject our results to stability criteria based on extreme ultraviolet radiation, as well as Roche-lobe overflow driven mass-loss and construct mass-radius relationships for the considered objects. We conclude by discussing observational avenues that may be used to confirm or repudiate the existence of putative low mass, gas-dominated planets.

  5. The Gould Belt 'MISFITS' Survey: The Real Solar Neighborhood Protostars

    NASA Astrophysics Data System (ADS)

    Heiderman, Amanda; Evans, Neal J., II

    2015-06-01

    We present an HCO+ J=3\\to 2 survey of Class 0+I and Flat SED young stellar objects (YSOs) found in the Gould Belt clouds by surveys with Spitzer. Our goal is to provide a uniform Stage 0+I source indicator for these embedded protostar candidates. We made single point HCO+ J=3\\to 2 measurements toward the source positions at the CSO and APEX of 546 YSOs (89% of the Class 0+I + Flat SED sample). Using the criteria from van Kempen et al., we classify sources as Stage 0+I or bona fide protostars and find that 84% of detected sources meet the criteria. We recommend a timescale for the evolution of Stage 0+I (embedded protostars) of 0.54 Myr. We find significant correlations of HCO+ integrated intensity with α and Tbol but not with Lbol. The detection fraction increases smoothly as a function of α and Lbol, while decreasing smoothly with Tbol. Using the Stage 0+I sources tightens the relation between protostars and high extinction regions of the cloud; 89% of Stage I sources lie in regions with AV > 8 mag. Class 0+I and Flat SED YSOs that are not detected in HCO+ have, on average, a factor of ∼2 higher Tbol and a factor of ∼5 lower Lbol than YSOs with HCO+ detections. We find less YSO contamination, defined as the number of undetected YSOs divided by the total number surveyed, for sources with Tbol ≲ 600 K and Lbol ≳ 1 L⊙. The contamination percentage is >90% at AV < 4 mag and decreases as AV increases.

  6. Formation of massive protostars in atomic cooling haloes

    NASA Astrophysics Data System (ADS)

    Becerra, Fernando; Greif, Thomas H.; Springel, Volker; Hernquist, Lars E.

    2015-01-01

    We present the highest-resolution three-dimensional simulation to date of the collapse of an atomic cooling halo in the early Universe. We use the moving-mesh code AREPO with the primordial chemistry module introduced in Greif, which evolves the chemical and thermal rate equations for over more than 20 orders of magnitude in density. Molecular hydrogen cooling is suppressed by a strong Lyman-Werner background, which facilitates the near-isothermal collapse of the gas at a temperature of about 104 K. Once the central gas cloud becomes optically thick to continuum emission, it settles into a Keplerian disc around the primary protostar. The initial mass of the protostar is about 0.1 M⊙, which is an order of magnitude higher than in minihaloes that cool via molecular hydrogen. The high accretion rate and efficient cooling of the gas catalyse the fragmentation of the disc into a small protostellar system with 5-10 members. After about 12 yr, strong gravitational interactions disrupt the disc and temporarily eject the primary protostar from the centre of the cloud. By the end of the simulation, a secondary clump has collapsed at a distance of ≃ 150 au from the primary clump. If this clump undergoes a similar evolution as the first, the central gas cloud may evolve into a wide binary system. High accretion rates of both the primary and secondary clumps suggest that fragmentation is not a significant barrier for forming at least one massive black hole seed.

  7. Clouds in Low-mass, Low-density Planets

    NASA Astrophysics Data System (ADS)

    Morley, Caroline; Fortney, J.; Marley, M.; Kempton, E.; Visscher, C.; Zahnle, K.

    2013-10-01

    The Kepler Space Telescope has revealed huge populations of low-mass, low-density planets, but their compositions remain elusive. For example, the density of GJ 1214b is consistent with either a water-world with a water atmosphere or a rock-iron core with a H/He envelope. Other super-Earths must contain hydrogen and helium to match their observed masses and radii. To understand this population of objects, we must be able to characterize their compositions through spectroscopy. The formation of clouds in exoplanet atmospheres significantly changes their observable spectra. For exoplanets, the opacity of hazes or clouds has been invoked as a possible explanation for the observed flat transmission spectrum of transiting super-Earth GJ 1214b as well as for the strong Rayleigh scattering feature in HD 189733b, the best-studied hot Jupiter. Here, we examine the effect of clouds on low-mass, low-density exoplanet spectra. We include the condensates that are present in chemical equilibrium for objects at these temperatures (500-900 K) which include minerals like sulfides and alkali salts. The most important of these clouds are sodium sulfide, potassium chloride, and zinc sulfide. These clouds should be most prominent at low surface gravity, strongly super-solar atmospheric abundances, and at the slant viewing geometry appropriate for transits. Hence they could be quite important for affecting the transmission spectra of cool low density super-Earth and Neptune-class planets. Another class of clouds may also dramatically alter the spectra of irradiated planets: photochemical hazes. We additionally include a hydrocarbon haze layer similar to the tholin haze in Titan’s atmosphere. We calculate the location and density of the haze layer using photochemical models from Kempton et al. 2012. We present new results that show that for enhanced metallicity atmospheres, either the clouds that form in equilibrium or a hydrocarbon haze layer could become sufficiently optically thick

  8. Properties of Protostars in the Elephant Trunk in the Globule IC 1396A

    NASA Astrophysics Data System (ADS)

    Reach, William T.; Faied, Dohy; Rho, Jeonghee; Boogert, Adwin; Tappe, Achim; Jarrett, Thomas H.; Morris, Patrick; Cambrésy, Laurent; Palla, Francesco; Valdettaro, Riccardo

    2009-01-01

    bright Hα emission; therefore, they are young, disk-bearing, classical T Tauri stars. The disk properties change significantly with source luminosity: low-mass (G-K) stars have prominent 9-11 emission features due to amorphous silicates while higher-mass (A-F) stars have weaker features requiring abundant crystalline silicates. A mineralogical model that fits the wide- and low-amplitude silicate feature of IC 1396A:θ requires small grains of crystalline olivine (11.3 μm peak) and another material to to explain its 9.1 μm peak; reasonable fits are obtained with a phyllosilicate, quartz, or relatively large (greater than 10 μm) amorphous olivine grains. The distribution of Class I sources is concentrated within the molecular globule, while the Class II sources are more widely scattered. Combined with the spectral results, this suggests two phases of star formation, the first (4 Myr ago) leading to the widespread Class II sources and the central O star of IC 1396 and the second (less than 1 Myr ago) occurring within the globule. The recent phase was likely triggered by the wind and radiation of the central O star of the IC 1396 H II region.

  9. Feedback in low-mass galaxies in the early Universe.

    PubMed

    Erb, Dawn K

    2015-07-01

    The formation, evolution and death of massive stars release large quantities of energy and momentum into the gas surrounding the sites of star formation. This process, generically termed 'feedback', inhibits further star formation either by removing gas from the galaxy, or by heating it to temperatures that are too high to form new stars. Observations reveal feedback in the form of galactic-scale outflows of gas in galaxies with high rates of star formation, especially in the early Universe. Feedback in faint, low-mass galaxies probably facilitated the escape of ionizing radiation from galaxies when the Universe was about 500 million years old, so that the hydrogen between galaxies changed from neutral to ionized-the last major phase transition in the Universe. PMID:26156371

  10. Exploring Low-Mass Dark Matter with CRESST

    NASA Astrophysics Data System (ADS)

    Strauss, R.; Angloher, G.; Bento, A.; Bucci, C.; Canonica, L.; Defay, X.; Erb, A.; Feilitzsch, F. v.; Ferreiro Iachellini, N.; Gorla, P.; Gütlein, A.; Hauff, D.; Jochum, J.; Kiefer, M.; Kluck, H.; Kraus, H.; Lanfranchi, J. C.; Loebell, J.; Münster, A.; Pagliarone, C.; Petricca, F.; Potzel, W.; Pröbst, F.; Reindl, F.; Schäffner, K.; Schieck, J.; Schönert, S.; Seidel, W.; Stodolsky, L.; Strandhagen, C.; Tanzke, A.; Trinh Thi, H. H.; Türkoglu, C.; Uffinger, M.; Ulrich, A.; Usherov, I.; Wawoczny, S.; Willers, M.; Wüstrich, M.; Zöller, A.

    2016-01-01

    The CRESST-II (Cryogenic Rare Event Search with Superconducting Thermometers) experiment, whose second phase has been successfully finished in summer 2015, aims at the direct detection of dark matter particles. The intrinsic radiopurity of CaWO_4 crystals, the capability to reject recoil events from alpha-surface contamination, and the energy threshold were significantly improved compared to previous runs of the experiment. A moderate exposure of 29 kg-days acquired by one ˜ 250 g CaWO_4 detector provides competitive limits on the spin-independent dark matter particle-nucleon cross section and probes a new region of parameter space for dark matter particle masses below 3 GeV/c^2 . The potential for low-mass dark matter particle search can be further exploited by a new detector design planned for CRESST-III. We describe the experimental strategy for the near future and give projections for the sensitivity.

  11. New low-mass member candidates of Taurus

    NASA Astrophysics Data System (ADS)

    Perger, M.; Lodieu, N.; Martín, E. L.; Barrado, D.

    A widely used tool to characterise the formation of stars is the initial mass function (IMF). It has been suggested that it departs significantly from the universal form in Taurus. To bring them into agreement, about 330 new low-mass members need to be identified. We aim to find those objects in an area located 5 deg to the north of the main clouds. We analysed the already known Taurus members and found in our UKIDSS GCS-based data sample 253 objects showing similar characteristics. 43 of those new member candidates were observed spectroscopically. 11 of them show strong signs for membership to the region. Since we observed only 17% of our selection, we would expect up to 65 objects in our hunting ground. Those numbers indicate a possible unknown population of Taurus away from the main clouds. The answer to whether the IMF of Taurus is different might be located in its off-cloud parts.

  12. Mass-luminosity relation of low mass stars.

    NASA Astrophysics Data System (ADS)

    Malkov, O. Yu.; Piskunov, A. E.; Shpil'Kina, D. A.

    1997-04-01

    The data on dynamic masses and multicolor photometry of 56 M-type components of binary/multiple systems was collected. Critical evaluation of late type stars bolometric correction scales have been performed. Our refined and reduced data is compared with published empirical and theoretical mass-luminosity relations. Our data does not exclude the existence of a step-like feature at M_V_=12mag. The best agreement between observations and theoretical models is found for recent calculations of D'Antona & Mazzitelli (1994ApJS...90..467D) with Alexander opacities. We conclude that present-day knowledge of the mass-luminosity relation at faintest magnitudes is not sufficient for making definite conclusions on the initial mass function of low mass stars.

  13. Low-Mass Bias Issues in Tomographic Gamma Scanning (TGS)

    SciTech Connect

    Estep, R. J.

    2001-01-01

    The term 'low-mass bias' has been used informally in TGS assays to describe systematic errors that arise from zero truncation in the emission image reconstruction. Emission image reconstruction algorithms used in TGS are constrained to give a non-negative result in every image voxel, so repeated assays of samples with low plutonium mass using these algorithms can give results that are high on average. We show that this problem can be avoided by formulating the TGS assay as the total net count rate for the scan times a matrix correction factor derived from the emission image, rather than as the sum of the individual emission image voxel masses. We also show that this formulation is automatically attained in reconstruction algorithms that preserve the total count rate in projections and that any reconstruction algorithm can be forced into this form by a simple normalization of the mass image.

  14. Low-Mass Inflation Systems for Inflatable Structures

    NASA Technical Reports Server (NTRS)

    Thunnissen, Daniel P.; Webster, Mark S.; Engelbrecht, Carl S.

    1995-01-01

    The use of inflatable space structures has often been proposed for aerospace and planetary applications. Communication, power generation, and very-long-baseline interferometry are just three potential applications of inflatable technology. The success of inflatable structures depends on the development of an applications of inflatable technology. This paper describes two design studies performed to develop a low mass inflation system. The first study takes advantage of existing onboard propulsion gases to reduce the overall system mass. The second study assumes that there is no onboard propulsion system. Both studies employ advanced components developed for the Pluto fast flyby spacecraft to further reduce mass. The study examined four different types of systems: hydrazine, nitrogen and water, nitrogen, and xenon. This study shows that all of these systems can be built for a small space structure with masses lower than 0.5 kilograms.

  15. Formation of elongated galaxies with low masses at high redshift

    NASA Astrophysics Data System (ADS)

    Ceverino, Daniel; Primack, Joel; Dekel, Avishai

    2015-10-01

    We report the identification of elongated (triaxial or prolate) galaxies in cosmological simulations at z ≃ 2. These are preferentially low-mass galaxies (M* ≤ 109.5 M⊙), residing in dark matter (DM) haloes with strongly elongated inner parts, a common feature of high-redshift DM haloes in the Λ cold dark matter cosmology. Feedback slows formation of stars at the centres of these haloes, so that a dominant and prolate DM distribution gives rise to galaxies elongated along the DM major axis. As galaxies grow in stellar mass, stars dominate the total mass within the galaxy half-mass radius, making stars and DM rounder and more oblate. A large population of elongated galaxies produces a very asymmetric distribution of projected axis ratios, as observed in high-z galaxy surveys. This indicates that the majority of the galaxies at high redshifts are not discs or spheroids but rather galaxies with elongated morphologies.

  16. Dust discs around low-mass main-sequence stars

    NASA Technical Reports Server (NTRS)

    Wolstencroft, R. D.; Walker, Helen J.

    1988-01-01

    The current understanding of the formation of circumstellar disks as a natural accompaniment to the process of low-mass star formation is examined. Models of the thermal emission from the dust disks around the prototype stars Alpha Lyr, Alpha PsA, Beta Pic, and Epsilon Eri are discussed, which indicate that the central regions of three of these disks are almost devoid of dust within radii ranging between 17 and 26 AU, with the temperature of the hottest zone lying between about 115 and 210 K. One possible explanation of the dust-free zones is the presence of a planet at the inner boundary of each cloud which sweeps up grains crossing its orbit.

  17. Exploring Low-Mass Dark Matter with CRESST

    NASA Astrophysics Data System (ADS)

    Strauss, R.; Angloher, G.; Bento, A.; Bucci, C.; Canonica, L.; Defay, X.; Erb, A.; Feilitzsch, F. v.; Ferreiro Iachellini, N.; Gorla, P.; Gütlein, A.; Hauff, D.; Jochum, J.; Kiefer, M.; Kluck, H.; Kraus, H.; Lanfranchi, J. C.; Loebell, J.; Münster, A.; Pagliarone, C.; Petricca, F.; Potzel, W.; Pröbst, F.; Reindl, F.; Schäffner, K.; Schieck, J.; Schönert, S.; Seidel, W.; Stodolsky, L.; Strandhagen, C.; Tanzke, A.; Trinh Thi, H. H.; Türkoglu, C.; Uffinger, M.; Ulrich, A.; Usherov, I.; Wawoczny, S.; Willers, M.; Wüstrich, M.; Zöller, A.

    2016-08-01

    The CRESST-II (Cryogenic Rare Event Search with Superconducting Thermometers) experiment, whose second phase has been successfully finished in summer 2015, aims at the direct detection of dark matter particles. The intrinsic radiopurity of CaWO_4 crystals, the capability to reject recoil events from alpha-surface contamination, and the energy threshold were significantly improved compared to previous runs of the experiment. A moderate exposure of 29 kg-days acquired by one ˜ 250 g CaWO_4 detector provides competitive limits on the spin-independent dark matter particle-nucleon cross section and probes a new region of parameter space for dark matter particle masses below 3 GeV/c^2. The potential for low-mass dark matter particle search can be further exploited by a new detector design planned for CRESST-III. We describe the experimental strategy for the near future and give projections for the sensitivity.

  18. Optimizing Cryogenic Detectors for Low-Mass WIMP Searches

    NASA Astrophysics Data System (ADS)

    Arnaud, Q.; Billard, J.; Juillard, A.

    2016-07-01

    This paper describes the methodology and results from a study dedicated to the optimization of cryogenic detectors for low-mass WIMP searches. Considering a data-driven background model from the EDELWEISS-III experiment, and two analysis methods, namely profile likelihood and boosted decision tree, we indentify the main experimental constraints and performances that have to be improved. We found that there is a clear difference in how to optimize the detector setup whether focusing on WIMPs with masses below 5 GeV or above. Finally, in the case of a hundred-kg scale experiment, we discuss the requirements to probe most of the parameter space region delimited by the ultimate neutrino bound below 6 GeV.

  19. HIGH-PRECISION DYNAMICAL MASSES OF VERY LOW MASS BINARIES

    SciTech Connect

    Konopacky, Q. M.; Ghez, A. M.; McLean, I. S.; Barman, T. S.; Rice, E. L.; Bailey, J. I.; White, R. J.; Duchene, G. E-mail: ghez@astro.ucla.ed E-mail: barman@lowell.ed E-mail: white@chara.gsu.ed

    2010-03-10

    We present the results of a three year monitoring program of a sample of very low mass (VLM) field binaries using both astrometric and spectroscopic data obtained in conjunction with the laser guide star adaptive optics system on the W. M. Keck II 10 m telescope. Among the 24 systems studied, 15 have undergone sufficient orbital motion, allowing us to derive their relative orbital parameters and hence their total system mass. These measurements more than double the number of mass measurements for VLM objects, and include the most precise mass measurement to date (<2%). Among the 11 systems with both astrometric and spectroscopic measurements, six have sufficient radial velocity variations to allow us to obtain individual component masses. This is the first derivation of the component masses for five of these systems. Altogether, the orbital solutions of these low mass systems show a correlation between eccentricity and orbital period, consistent with their higher mass counterparts. In our primary analysis, we find that there are systematic discrepancies between our dynamical mass measurements and the predictions of theoretical evolutionary models (TUCSON and LYON) with both models either underpredicting or overpredicting the most precisely determined dynamical masses. These discrepancies are a function of spectral type, with late-M through mid-L systems tending to have their masses underpredicted, while one T-type system has its mass overpredicted. These discrepancies imply that either the temperatures predicted by evolutionary and atmosphere models are inconsistent for an object of a given mass, or the mass-radius relationship or cooling timescales predicted by the evolutionary models are incorrect. If these spectral-type trends are correct and hold into the planetary mass regime, the implication is that the masses of directly imaged extrasolar planets are overpredicted by the evolutionary models.

  20. Thermohaline mixing in evolved low-mass stars

    NASA Astrophysics Data System (ADS)

    Cantiello, M.; Langer, N.

    2010-10-01

    Context. Thermohaline mixing has recently been proposed to occur in low-mass red giants, with large consequence for the chemical yields of low-mass stars. Aims: We investigate the role of thermohaline mixing during the evolution of stars between 1 M_⊙ and 3 M_⊙, in comparison with other mixing processes acting in these stars. Methods: We use a stellar evolution code which includes rotational mixing, internal magnetic fields and thermohaline mixing. Results: We confirm that during the red giant stage, thermohaline mixing has the potential to decrease the abundance of 3He, which is produced earlier on the main sequence. In our models we find that this process is working on the RGB only in stars with initial mass M ⪉ 1.5 M_⊙. Moreover we report that thermohaline mixing is also present during core He-burning and beyond, and has the potential to change the surface abundances of AGB stars. While we find rotational and magnetic mixing to be negligible compared to the thermohaline mixing in the relevant layers, the interaction of thermohaline motions with the differential rotation may be essential to establish the timescale of thermohaline mixing in red giants. Conclusions: To explain the surface abundances observed at the bump in the luminosity function, the speed of the mixing process needs to be more than two orders of magnitude higher than in our models. However it is not clear if thermohaline mixing is the only physical process responsible for these surface-abundance anomalies. Therefore it is not possible at this stage to calibrate the efficiency of thermohaline mixing against the observations.

  1. Low Mass Printable Devices for Energy Capture, Storage, and Use

    NASA Technical Reports Server (NTRS)

    Frazier, Donald O.; Singer, Christopher E.; Rogers, Jan R.; Schramm, Harry F.; Fabisinski, Leo L.; Lowenthal, Mark; Ray, William J.; Fuller, Kirk A.

    2010-01-01

    The energy-efficient, environmentally friendly technology that will be presented is the result of a Space Act Agreement between NthDegree Technologies Worldwide, Inc., and the National Aeronautics and Space Administration's (NASA's) Marshall Space Flight Center (MSFC). The work combines semiconductor and printing technologies to advance lightweight electronic and photonic devices having excellent potential for commercial and exploration applications. Device development involves three projects that relate to energy generation and consumption: (1) a low-mass efficient (low power, low heat emission) micro light-emitting diode (LED) area lighting device; (2) a low-mass omni-directional efficient photovoltaic (PV) device with significantly improved energy capture; and (3) a new approach to building super-capacitors. These three technologies, energy capture, storage, and usage (e.g., lighting), represent a systematic approach for building efficient local micro-grids that are commercially feasible; furthermore, these same technologies, appropriately replacing lighting with lightweight power generation, will be useful for enabling inner planetary missions using smaller launch vehicles and to facilitate surface operations during lunar and planetary surface missions. The PV device model is a two sphere, light trapped sheet approximately 2-mm thick. The model suggests a significant improvement over current thin film systems. For lighting applications, all three technology components are printable in-line by printing sequential layers on a standard screen or flexographic direct impact press using the three-dimensional printing technique (3DFM) patented by NthDegree. One primary contribution to this work in the near term by the MSFC is to test the robustness of prototype devices in the harsh environments that prevail in space and on the lunar surface. It is anticipated that this composite device, of which the lighting component has passed off-gassing testing, will function

  2. Empirical Isochrones for Low Mass Stars in Nearby Young Associations

    NASA Astrophysics Data System (ADS)

    Herczeg, Gregory J.; Hillenbrand, Lynne A.

    2015-07-01

    Absolute ages of young stars are important for many issues in pre-main-sequence stellar and circumstellar evolution but long have been recognized as difficult to derive and calibrate. In this paper, we use literature spectral types and photometry to construct empirical isochrones in Hertzsprung-Russell diagrams for low mass stars and brown dwarfs in the η Cha, ɛ Cha, and TW Hya Associations and the β Pic and Tuc-Hor Moving Groups. A successful theory of pre-main-sequence evolution should match the shapes of the stellar loci for these groups of young stars. However, when comparing the combined empirical isochrones to isochrones predicted from evolutionary models, discrepancies lead to a spectral type (mass) dependence in stellar age estimates. Improved prescriptions for convection and boundary conditions in the latest models of pre-main-sequence evolution lead to a significantly improved correspondence between empirical and model isochrones, with small offsets at low temperatures that may be explained by observational uncertainties or by model limitations. Independent of model predictions, linear fits to combined stellar loci of these regions provide a simple empirical method to order clusters by luminosity with a reduced dependence on spectral type. Age estimates calculated from various sets of modern models that reproduce Li depletion boundary ages of the β Pic Moving Group also imply a ˜4 Myr age for the low mass members of the Upper Sco OB Association, which is younger than the 11 Myr age that has been recently estimated for intermediate and high mass members.

  3. Fast migration of low-mass planets in radiative discs

    NASA Astrophysics Data System (ADS)

    Pierens, A.

    2015-12-01

    Low-mass planets are known to undergo Type I migration and this process must have played a key role during the evolution of planetary systems. Analytical formulae for the disc torque have been derived assuming that the planet evolves on a fixed circular orbit. However, recent work has shown that in isothermal discs, a migrating protoplanet may also experience dynamical corotation torques that scale with the planet drift rate. The aim of this study is to examine whether dynamical corotation torques can also affect the migration of low-mass planets in non-isothermal discs. We performed 2D radiative hydrodynamical simulations to examine the orbital evolution outcome of migrating protoplanets as a function of disc mass. We find that a protoplanet can enter a fast migration regime when it migrates in the direction set by the entropy-related horseshoe drag and when the Toomre stability parameter is less than a threshold value below which the horseshoe region contracts into a tadpole-like region. In that case, an underdense trapped region appears near the planet, with an entropy excess compared to the ambient disc. If the viscosity and thermal diffusivity are small enough so that the entropy excess is conserved during migration, the planet then experiences strong corotation torques arising from the material flowing across the planet orbit. During fast migration, we observe that a protoplanet can pass through the zero-torque line predicted by static torques. We also find that fast migration may help in disrupting the mean-motion resonances that are formed by convergent migration of embryos.

  4. Dynamical structure of the inner 100 AU of the deeply embedded protostar IRAS 16293–2422

    SciTech Connect

    Favre, Cécile; Field, David; Jørgensen, Jes K.; Brinch, Christian; Bisschop, Suzanne E.; Bourke, Tyler L.; Hogerheijde, Michiel R.; Frieswijk, Wilfred W. F.

    2014-07-20

    A fundamental question about the early evolution of low-mass protostars is when circumstellar disks may form. High angular resolution observations of molecular transitions in the (sub)millimeter wavelength windows make it possible to investigate the kinematics of the gas around newly formed stars, for example, to identify the presence of rotation and infall. IRAS 16293–2422 was observed with the extended Submillimeter Array (eSMA) resulting in subarcsecond resolution (0.''46 × 0.''29, i.e., ∼55 × 35 AU) images of compact emission from the C{sup 17}O (3-2) and C{sup 34}S (7-6) transitions at 337 GHz (0.89 mm). To recover the more extended emission we have combined the eSMA data with SMA observations of the same molecules. The emission of C{sup 17}O (3-2) and C{sup 34}S (7-6) both show a velocity gradient oriented along a northeast-southwest direction with respect to the continuum marking the location of one of the components of the binary, IRAS 16293A. Our combined eSMA and SMA observations show that the velocity field on the 50-400 AU scales is consistent with a rotating structure. It cannot be explained by simple Keplerian rotation around a single point mass but rather needs to take into account the enclosed envelope mass at the radii where the observed lines are excited. We suggest that IRAS 16293–2422 could be among the best candidates to observe a pseudo-disk with future high angular resolution observations.

  5. Change in the chemical composition of infalling gas forming a disk around a protostar.

    PubMed

    Sakai, Nami; Sakai, Takeshi; Hirota, Tomoya; Watanabe, Yoshimasa; Ceccarelli, Cecilia; Kahane, Claudine; Bottinelli, Sandrine; Caux, Emmanuel; Demyk, Karine; Vastel, Charlotte; Coutens, Audrey; Taquet, Vianney; Ohashi, Nagayoshi; Takakuwa, Shigehisa; Yen, Hsi-Wei; Aikawa, Yuri; Yamamoto, Satoshi

    2014-03-01

    IRAS 04368+2557 is a solar-type (low-mass) protostar embedded in a protostellar core (L1527) in the Taurus molecular cloud, which is only 140 parsecs away from Earth, making it the closest large star-forming region. The protostellar envelope has a flattened shape with a diameter of a thousand astronomical units (1 AU is the distance from Earth to the Sun), and is infalling and rotating. It also has a protostellar disk with a radius of 90 AU (ref. 6), from which a planetary system is expected to form. The interstellar gas, mainly consisting of hydrogen molecules, undergoes a change in density of about three orders of magnitude as it collapses from the envelope into the disk, while being heated from 10 kelvin to over 100 kelvin in the mid-plane, but it has hitherto not been possible to explore changes in chemical composition associated with this collapse. Here we report that the unsaturated hydrocarbon molecule cyclic-C3H2 resides in the infalling rotating envelope, whereas sulphur monoxide (SO) is enhanced in the transition zone at the radius of the centrifugal barrier (100 ± 20 AU), which is the radius at which the kinetic energy of the infalling gas is converted to rotational energy. Such a drastic change in chemistry at the centrifugal barrier was not anticipated, but is probably caused by the discontinuous infalling motion at the centrifugal barrier and local heating processes there. PMID:24522533

  6. Leo P: An Unquenched Very Low-mass Galaxy

    NASA Astrophysics Data System (ADS)

    McQuinn, Kristen B. W.; Skillman, Evan D.; Dolphin, Andrew; Cannon, John M.; Salzer, John J.; Rhode, Katherine L.; Adams, Elizabeth A. K.; Berg, Danielle; Giovanelli, Riccardo; Girardi, Léo; Haynes, Martha P.

    2015-10-01

    Leo P is a low-luminosity dwarf galaxy discovered through the blind H i Arecibo Legacy Fast ALFA survey. The H i and follow-up optical observations have shown that Leo P is a gas-rich dwarf galaxy with active star formation, an underlying older population, and an extremely low oxygen abundance. We have obtained optical imaging with the Hubble Space Telescope to two magnitudes below the red clump in order to study the evolution of Leo P. We refine the distance measurement to Leo P to be 1.62 ± 0.15 Mpc, based on the luminosity of the horizontal branch stars and 10 newly identified RR Lyrae candidates. This places the galaxy at the edge of the Local Group, ˜0.4 Mpc from Sextans B, the nearest galaxy in the NGC 3109 association of dwarf galaxies of which Leo P is clearly a member. The star responsible for ionizing the H ii region is most likely an O7V or O8V spectral type, with a stellar mass ≳25 M⊙. The presence of this star provides observational evidence that massive stars at the upper end of the initial mass function are capable of being formed at star formation rates as low as ˜10-5 M⊙ yr-1. The best-fitting star formation history (SFH) derived from the resolved stellar populations of Leo P using the latest PARSEC models shows a relatively constant star formation rate over the lifetime of the galaxy. The modeled luminosity characteristics of Leo P at early times are consistent with low-luminosity dSph Milky Way satellites, suggesting that Leo P is what a low-mass dSph would look like if it evolved in isolation and retained its gas. Despite the very low mass of Leo P, the imprint of reionization on its SFH is subtle at best, and consistent with being totally negligible. The isolation of Leo P, and the total quenching of star formation of Milky Way satellites of similar mass, implies that the local environment dominates the quenching of the Milky Way satellites. Based on observations made with the NASA/ESA Hubble Space Telescope (HST), obtained from the

  7. Chandra Observation of Polaris: Census of Low-Mass Companions

    NASA Astrophysics Data System (ADS)

    Evans, Nancy Remage; Wolk, Scott; Guinan, Edward; Engle, Scott; Schlegel, Eric; Mason, Brian; Karovska, Margarita; Spitzbart, Bradley

    2009-09-01

    We have observed Polaris = HD 8890 with Chandra ACIS-I for 10 ksec and found an X-ray source at the location of the Cepheid Polaris A = Aa + Ab with log L_X = 28.89 ergs s^{-1} and a kT = 0.6 keV. Either the F7 Ib supergiant or the F6 V spectroscopic companion could produce a spectrum this soft. Polaris B is not an X-ray source, which is consistent with its early F spectral type. However, this shows that it does not itself have a lower mass companion. Two resolved low mass stars ``C and D" are not physical companions based on the lack of X-rays (indicating an older age than the Cepheid) and inconsistent motion. In addition, a possible more distant companion is identified, and also less plausible one. Thus, this observation provides a complete census of companions down to masses as small as an order of magnitude less than the Cepheid and nearly 15 mag fainter within the surrounding 0.1 pc.Funding for this work was provided by Chandra grant GO6-7011A Chandra X-ray Center NASA Contract NAS8-39073

  8. The low mass ratio contact binary system V728 Herculis

    NASA Astrophysics Data System (ADS)

    Erkan, N.; Ulaş, B.

    2016-07-01

    We present the orbital period study and the photometric analysis of the contact binary system V728 Her. Our orbital period analysis shows that the period of the system increases (dP / dt = 1.92 ×10-7 dyr-1) and the mass transfer rate from the less massive component to more massive one is 2.51 ×10-8 M⊙y-1 . In addition, an advanced sinusoidal variation in period can be attributed to the light-time effect by a tertiary component or the Applegate mechanism triggered by the secondary component. The simultaneous multicolor BVR light and radial velocity curves solution indicates that the physical parameters of the system are M1 = 1.8M⊙ , M2 = 0.28M⊙ , R1 = 1.87R⊙ , R2 = 0.82R⊙ , L1 = 5.9L⊙ , and L2 = 1.2L⊙ . We discuss the evolutionary status and conclude that V728 Her is a deep (f = 81%), low mass ratio (q = 0.16) contact binary system.

  9. 3D lumped LC resonators as low mass axion haloscopes

    NASA Astrophysics Data System (ADS)

    McAllister, Ben T.; Parker, Stephen R.; Tobar, Michael E.

    2016-08-01

    The axion is a hypothetical particle considered to be the most economical solution to the strong C P problem. It can also be formulated as a compelling component of dark matter. The haloscope, a leading axion detection scheme, relies on the conversion of galactic halo axions into real photons inside a resonant cavity structure in the presence of a static magnetic field, where the generated photon frequency corresponds to the mass of the axion. For maximum sensitivity it is key that the central frequency of the cavity mode structure coincides with the frequency of the generated photon. As the mass of the axion is unknown, it is necessary to perform searches over a wide range of frequencies. Currently there are substantial regions of the promising preinflationary low-mass axion range without any viable proposals for experimental searches. We show that three-dimensional resonant LC circuits with separated magnetic and electric fields, commonly known as reentrant cavities, can be sensitive dark matter haloscopes in this region, with frequencies inherently lower than those achievable in the equivalent size of empty resonant cavity. We calculate the sensitivity and accessible axion mass range of these experiments, designing geometries to exploit and maximize the separated magnetic and electric coupling of the axion to the cavity mode.

  10. Discovery of a Low-mass Companion Around HR 3549

    NASA Astrophysics Data System (ADS)

    Mawet, D.; David, T.; Bottom, M.; Hinkley, S.; Stapelfeldt, K.; Padgett, D.; Mennesson, B.; Serabyn, E.; Morales, F.; Kuhn, J.

    2015-10-01

    We report the discovery of a low-mass companion to HR 3549, an A0V star surrounded by a debris disk with a warm excess detected by WISE at 22 μm (10σ significance). We imaged HR 3549 B in the L band with NAOS-CONICA, the adaptive optics infrared camera of the Very Large Telescope, in January 2013 and confirmed its common proper motion in 2015 January. The companion is at a projected separation of ≃80 AU and position angle of ≃157°, so it is orbiting well beyond the warm disk inner edge of r > 10 AU. Our age estimate for this system corresponds to a companion mass in the range 15–80 MJ, spanning the brown dwarf regime, and so HR 3549 B is another recent addition to the growing list of brown dwarf desert objects with extreme mass ratios. The simultaneous presence of a warm disk and a brown dwarf around HR 3549 provides interesting empirical constraints on models of the formation of substellar companions.