Atlas of low-mass young stellar object disks from mid-infrared interferometry

NASA Astrophysics Data System (ADS)

Varga, J.; Ábrahám, P.; Ratzka, Th.; Menu, J.; Gabányi, K.; Kóspál, Á.; van Boekel, R.; Mosoni, L.; Henning, Th.

We present our approach of visibility modeling of disks around low-mass (< 2 M ⊙) young stellar objects (YSOs). We compiled an atlas based on mid-infrared interferometric observations from the MIDI instrument at the VLTI. We use three different models to fit the data. These models allow us to determine overall sizes (and the extent of the inner gaps) of the modeled circumstellar disks.

Multiplicity among Young Brown Dwarfs and Very Low Mass Stars

NASA Astrophysics Data System (ADS)

Ahmic, Mirza; Jayawardhana, Ray; Brandeker, Alexis; Scholz, Alexander; van Kerkwijk, Marten H.; Delgado-Donate, Eduardo; Froebrich, Dirk

2007-12-01

We report on a near-infrared adaptive optics imaging survey of 31 young brown dwarfs and very low mass (VLM) stars, 28 of which are in the Chamaeleon I star-forming region, using the ESO Very Large Telescope. We resolve the suspected 0.16'' (~26 AU) binary Cha Hα 2 and present two new binaries, Hn 13 and CHXR 15, with separations of 0.13'' (~20 AU) and 0.30'' (~50 AU), respectively; the latter is one of the widest VLM systems known. We find a binary frequency of 11+9-6%, thus confirming the trend for a lower binary frequency with decreasing mass. By combining our work with previous surveys, we arrive at the largest sample of young VLM objects (72) with high angular resolution imaging to date. Its multiplicity fraction is in statistical agreement with that for VLM objects in the field. Furthermore, we note that many field stellar binaries with lower binding energies and/or wider cross sections have survived dynamical evolution and that statistical models suggest tidal disruption by passing stars is unlikely to affect the binary properties of our systems. Thus, we argue that there is no significant evolution of multiplicity with age among brown dwarfs and VLM stars in OB and T associations between a few megayears to several gigayears. Instead, the observations so far suggest that VLM objects are either less likely to be born in fragile multiple systems than solar-mass stars or such systems are disrupted very early. We dedicate this paper to the memory of our coauthor, Eduardo Delgado-Donate, who died in a hiking accident in Tenerife earlier this year.

ORBITAL SOLUTIONS FOR TWO YOUNG, LOW-MASS SPECTROSCOPIC BINARIES IN OPHIUCHUS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rosero, V.; Prato, L.; Wasserman, L. H.

2011-01-15

We report the orbital parameters for ROXR1 14 and RX J1622.7-2325Nw, two young, low-mass, and double-lined spectroscopic binaries recently discovered in the Ophiuchus star-forming region. Accurate orbital solutions were determined from over a dozen high-resolution spectra taken with the Keck II and Gemini South telescopes. These objects are T Tauri stars with mass ratios close to unity and periods of {approx}5 and {approx}3 days, respectively. In particular, RX J1622.7-2325Nw shows a non-circularized orbit with an eccentricity of 0.30, higher than any other short-period pre-main-sequence (PMS) spectroscopic binary known to date. We speculate that the orbit of RX J1622.7-2325Nw has notmore » yet circularized because of the perturbing action of a {approx}1'' companion, itself a close visual pair. A comparison of known young spectroscopic binaries (SBs) and main-sequence (MS) SBs in the eccentricity-period plane shows an indistinguishable distribution of the two populations, implying that orbital circularization occurs in the first 1 Myr of a star's lifetime. With the results presented in this paper we increase by {approx}4% the small sample of PMS spectroscopic binary stars with known orbital elements.« less

A HIGH-PRECISION NEAR-INFRARED SURVEY FOR RADIAL VELOCITY VARIABLE LOW-MASS STARS USING CSHELL AND A METHANE GAS CELL

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gagné, Jonathan; Plavchan, Peter; Gao, Peter

2016-05-01

We present the results of a precise near-infrared (NIR) radial velocity (RV) survey of 32 low-mass stars with spectral types K2–M4 using CSHELL at the NASA InfraRed Telescope Facility in the K band with an isotopologue methane gas cell to achieve wavelength calibration and a novel, iterative RV extraction method. We surveyed 14 members of young (≈25–150 Myr) moving groups, the young field star ε Eridani, and 18 nearby (<25 pc) low-mass stars and achieved typical single-measurement precisions of 8–15 m s{sup −1}with a long-term stability of 15–50 m s{sup −1} over longer baselines. We obtain the best NIR RVmore » constraints to date on 27 targets in our sample, 19 of which were never followed by high-precision RV surveys. Our results indicate that very active stars can display long-term RV variations as low as ∼25–50 m s{sup −1} at ≈2.3125 μ m, thus constraining the effect of jitter at these wavelengths. We provide the first multiwavelength confirmation of GJ 876 bc and independently retrieve orbital parameters consistent with previous studies. We recovered RV variabilities for HD 160934 AB and GJ 725 AB that are consistent with their known binary orbits, and nine other targets are candidate RV variables with a statistical significance of 3 σ –5 σ . Our method, combined with the new iSHELL spectrograph, will yield long-term RV precisions of ≲5 m s{sup −1} in the NIR, which will allow the detection of super-Earths near the habitable zone of mid-M dwarfs.« less

The Low-mass Population in the Young Cluster Stock 8: Stellar Properties and Initial Mass Function

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jose, Jessy; Herczeg, Gregory J.; Fang, Qiliang

The evolution of H ii regions/supershells can trigger a new generation of stars/clusters at their peripheries, with environmental conditions that may affect the initial mass function, disk evolution, and star formation efficiency. In this paper we study the stellar content and star formation processes in the young cluster Stock 8, which itself is thought to be formed during the expansion of a supershell. We present deep optical photometry along with JHK and 3.6 and 4.5 μ m photometry from UKIDSS and Spitzer -IRAC. We use multicolor criteria to identify the candidate young stellar objects in the region. Using evolutionary models,more » we obtain a median log(age) of ∼6.5 (∼3.0 Myr) with an observed age spread of ∼0.25 dex for the cluster. Monte Carlo simulations of the population of Stock 8, based on estimates for the photometric uncertainty, differential reddening, binarity, and variability, indicate that these uncertainties introduce an age spread of ∼0.15 dex. The intrinsic age spread in the cluster is ∼0.2 dex. The fraction of young stellar objects surrounded by disks is ∼35%. The K -band luminosity function of Stock 8 is similar to that of the Trapezium cluster. The initial mass function (IMF) of Stock 8 has a Salpeter-like slope at >0.5 M {sub ⊙} and flattens and peaks at ∼0.4 M {sub ⊙}, below which it declines into the substellar regime. Although Stock 8 is surrounded by several massive stars, there seems to be no severe environmental effect in the form of the IMF due to the proximity of massive stars around the cluster.« less

Binaries among low-mass stars in nearby young moving groups

NASA Astrophysics Data System (ADS)

Janson, Markus; Durkan, Stephen; Hippler, Stefan; Dai, Xiaolin; Brandner, Wolfgang; Schlieder, Joshua; Bonnefoy, Mickaël; Henning, Thomas

2017-03-01

The solar galactic neighborhood contains a number of young co-moving associations of stars (known as young moving groups) with ages of 10-150 Myr, which are prime targets for a range of scientific studies, including direct imaging planet searches. The late-type stellar populations of such groups still remain in their pre-main sequence phase, and are thus well suited for purposes such as isochronal dating. Close binaries are particularly useful in this regard since they allow for a model-independent dynamical mass determination. Here we present a dedicated effort to identify new close binaries in nearby young moving groups, through high-resolution imaging with the AstraLux Sur Lucky Imaging camera. We surveyed 181 targets, resulting in the detection of 61 companions or candidates, of which 38 are new discoveries. An interesting example of such a case is 2MASS J00302572-6236015 AB, which is a high-probability member of the Tucana-Horologium moving group, and has an estimated orbital period of less than 10 yr. Among the previously known objects is a serendipitous detection of the deuterium burning boundary circumbinary companion 2MASS J01033563-5515561 (AB)b in the z' band, thereby extending the spectral coverage for this object down to near-visible wavelengths. Based on observations collected at the European Southern Observatory, Chile (Programs 096.C-0243 and 097.C-0135).Tables 1-3 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/599/A70

Prediction equation for calculating fat mass in young Indian adults.

PubMed

Sandhu, Jaspal Singh; Gupta, Giniya; Shenoy, Shweta

2010-06-01

Accurate measurement or prediction of fat mass is useful in physiology, nutrition and clinical medicine. Most predictive equations currently used to assess percentage of body fat or fat mass, using simple anthropometric measurements were derived from people in western societies and they may not be appropriate for individuals with other genotypic and phenotypic characteristics. We developed equations to predict fat mass from anthropometric measurements in young Indian adults. Fat mass was measured in 60 females and 58 males, aged 20 to 29 yrs by using hydrostatic weighing and by simultaneous measurement of residual lung volume. Anthropometric measure included weight (kg), height (m) and 4 skinfold thickness [STs (mm)]. Sex specific linear regression model was developed with fat mass as the dependent variable and all anthropometric measures as independent variables. The prediction equation obtained for fat mass (kg) for males was 8.46+0.32 (weight) - 15.16 (height) + 9.54 (log of sum of 4 STs) (R2= 0. 53, SEE=3.42 kg) and - 20.22 + 0.33 (weight) + 3.44 (height) + 7.66 (log of sum of 4 STs) (R2=0.72, SEE=3.01kg) for females. A new prediction equation for the measurement of fat mass was derived and internally validated in young Indian adults using simple anthropometric measurements.

From Stars to Super-Planets: The Low-Mass IMF in the Young Cluster IC348

NASA Technical Reports Server (NTRS)

Najita, Joan R.; Tiede, Glenn P.; Carr, John S.

2000-01-01

We investigate the low-mass population of the young cluster IC348 down to the deuterium-burning limit, a fiducial boundary between brown dwarf and planetary mass objects, using a new and innovative method for the spectral classification of late-type objects. Using photometric indices, constructed from HST/NICMOS narrow-band imaging, that measure the strength of the 1.9 micron water band, we determine the spectral type and reddening for every M-type star in the field, thereby separating cluster members from the interloper population. Due to the efficiency of our spectral classification technique, our study is complete from approximately 0.7 solar mass to 0.015 solar mass. The mass function derived for the cluster in this interval, dN/d log M alpha M(sup 0.5), is similar to that obtained for the Pleiades, but appears significantly more abundant in brown dwarfs than the mass function for companions to nearby sun-like stars. This provides compelling observational evidence for different formation and evolutionary histories for substellar objects formed in isolation vs. as companions. Because our determination of the IMF is complete to very low masses, we can place interesting constraints on the role of physical processes such as fragmentation in the star and planet formation process and the fraction of dark matter in the Galactic halo that resides in substellar objects.

Prediction Equation for Calculating Fat Mass in Young Indian Adults

PubMed Central

Sandhu, Jaspal Singh; Gupta, Giniya; Shenoy, Shweta

2010-01-01

Purpose Accurate measurement or prediction of fat mass is useful in physiology, nutrition and clinical medicine. Most predictive equations currently used to assess percentage of body fat or fat mass, using simple anthropometric measurements were derived from people in western societies and they may not be appropriate for individuals with other genotypic and phenotypic characteristics. We developed equations to predict fat mass from anthropometric measurements in young Indian adults. Methods Fat mass was measured in 60 females and 58 males, aged 20 to 29 yrs by using hydrostatic weighing and by simultaneous measurement of residual lung volume. Anthropometric measure included weight (kg), height (m) and 4 skinfold thickness [STs (mm)]. Sex specific linear regression model was developed with fat mass as the dependent variable and all anthropometric measures as independent variables. Results The prediction equation obtained for fat mass (kg) for males was 8.46+0.32 (weight) − 15.16 (height) + 9.54 (log of sum of 4 STs) (R2= 0. 53, SEE=3.42 kg) and − 20.22 + 0.33 (weight) + 3.44 (height) + 7.66 (log of sum of 4 STs) (R2=0.72, SEE=3.01kg) for females. Conclusion A new prediction equation for the measurement of fat mass was derived and internally validated in young Indian adults using simple anthropometric measurements. PMID:22375197

Orbit of the young very low-mass spectroscopic binary CHXR 74

NASA Astrophysics Data System (ADS)

Joergens, V.; Janson, M.; Müller, A.

2012-01-01

The pre-main sequence star CHXR 74 (M4.25) in Chamaeleon I was found a few years ago to be a very low-mass spectroscopic binary. A determination of its mass would provide a valuable dynamical mass measurement at young ages in the poorly constrained mass regime of <0.3 M⊙. We carried out follow-up radial velocity monitoring with UVES/VLT between 2008 and 2011 and high-resolution adaptive-optic-assisted imaging with NACO/VLT in 2008 with the aim of constraining the binary orbit. We present an orbital solution of the system based on the combined radial velocity data set, which spans more than eleven years of UVES monitoring for CHXR 74. The best-fit Kepler model has an orbital period of 13.1 years, zero eccentricity, and a radial velocity semi-amplitude of 2.2 km s-1. A companion mass M2sini (which is a lower limit due to the unknown orbital inclination i) of 0.08 M⊙ is derived by using a model-dependent mass estimate for the primary of 0.24 M⊙. The binary separation (a1sini + a2) for an inclination of 90° is 3.8 AU, which corresponds to 23 mas. Complementary NACO/VLT images of CHXR 74 were taken with the aim to directly resolve the binary. While there are marginal signs of an extended point spread function (PSF), we have detected no convincing companion to CHXR 74 in the NACO images. From the non-detection of the companion together with a prediction of the binary separation at the time of the NACO observations, we derive an upper limit for the K-band brightness ratio of the two binary components of 0.5. This allows us to estimate an upper limit of the companion mass of 0.14 M⊙ by applying evolutionary models. Thus, we confirm that CHXR 74 is a very low-mass spectroscopic binary and constrain the secondary mass to lie within the range of about 0.08 and 0.14 M⊙. We predict an astrometric signal of the primary between 0.2 and 0.4 mas when taking into account the luminosity of the companion. The Gaia astrometric mission might well be able to solve the

A MODEL FOR (QUASI-)PERIODIC MULTIWAVELENGTH PHOTOMETRIC VARIABILITY IN YOUNG STELLAR OBJECTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kesseli, Aurora Y.; Petkova, Maya A.; Wood, Kenneth

We present radiation transfer models of rotating young stellar objects (YSOs) with hot spots in their atmospheres, inner disk warps, and other three-dimensional effects in the nearby circumstellar environment. Our models are based on the geometry expected from magneto-accretion theory, where material moving inward in the disk flows along magnetic field lines to the star and creates stellar hot spots upon impact. Due to rotation of the star and magnetosphere, the disk is variably illuminated. We compare our model light curves to data from the Spitzer YSOVAR project to determine if these processes can explain the variability observed at opticalmore » and mid-infrared wavelengths in young stars. We focus on those variables exhibiting “dipper” behavior that may be periodic, quasi-periodic, or aperiodic. We find that the stellar hot-spot size and temperature affects the optical and near-infrared light curves, while the shape and vertical extent of the inner disk warp affects the mid-IR light curve variations. Clumpy disk distributions with non-uniform fractal density structure produce more stochastic light curves. We conclude that magneto-accretion theory is consistent with certain aspects of the multiwavelength photometric variability exhibited by low-mass YSOs. More detailed modeling of individual sources can be used to better determine the stellar hot-spot and inner disk geometries of particular sources.« less

Low muscle mass is associated with metabolic syndrome only in nonobese young adults: the Korea National Health and Nutrition Examination Survey 2008-2010.

PubMed

Kim, Byung Chul; Kim, Mee Kyoung; Han, Kyungdo; Lee, Sae-Young; Lee, Seung-Hwan; Ko, Seung-Hyun; Kwon, Hyuk-Sang; Merchant, Anwar T; Yim, Hyeon Woo; Lee, Won-Chul; Park, Yong Gyu; Park, Yong-Moon

2015-12-01

Little is known about the relationship between body composition and metabolic risk factors in young adults. We hypothesized that low muscle mass (LMM) is associated with metabolic syndrome (MetS) and its components in young adults and that the associations vary by obesity. A cross-sectional analysis was conducted using the Korea National Health and Nutrition Examination Survey data. In total, 5300 young adults aged 19 to 39 years were evaluated. Low muscle mass was defined as an appendicular skeletal muscle mass/weight less than 1 SD below the mean for each participant's corresponding sex and age group. Obesity was defined as a body mass index greater than or equal to 25 kg/m2. The prevalence of LMM was higher in obese than nonobese participants (37.6% vs. 9.6%). In the nonobese participants, the prevalence of MetS, high waist circumference, high triglycerides, and high blood pressure was significantly greater in the LMM group than in the high muscle mass group. In the nonobese group, compared with high muscle mass participants, those with LMM had odds ratios for MetS of 3.6 (95% confidence interval, 1.48-8.76; P < .001) and 3.6 (95% confidence interval, 1.48-8.71; P < .001) in men and women, respectively, after adjusting for confounding factors. However, no significant association of LMM with MetS or its components was found in obese participants. In conclusion, our results suggest that young adults with LMM may have a high risk of MetS, especially when they are nonobese. Interventions aimed at increasing muscle mass at younger ages may have the potential to reduce MetS. Published by Elsevier Inc.

The Low End of the Initial Mass Function in Young Clusters. II. Evidence for Primordial Mass Segregation in NGC 330 in the Small Magellanic Cloud

NASA Astrophysics Data System (ADS)

Sirianni, Marco; Nota, Antonella; De Marchi, Guido; Leitherer, Claus; Clampin, Mark

2002-11-01

As part of a larger program aimed at investigating the universality of the initial mass function (IMF) at low masses in a number of young clusters in the LMC and SMC, we present a new study of the low end of the stellar IMF of NGC 330, the richest young star cluster in the SMC, from deep broadband V and I images obtained with HST/WFPC2. We detect stars down to a limiting magnitude of m555=24.9, which corresponds to stellar masses of ~0.8Msolar at the distance of the SMC. A comparison of the cluster color-magnitude diagram with theoretical evolutionary tracks indicates an age of ~30 Myr for NGC 330, in agreement with previous published results. We derive the cluster luminosity function, which we correct for background contamination using an adjacent SMC field, and construct the mass function in the 1-7Msolar mass range. Given the young cluster age, the MF can well approximate the IMF. We find that the IMF in the central cluster regions (within 30") is well reproduced by a power law with a slope consistent with Salpeter's. In addition, the richness of the cluster allows us to investigate the IMF as a function of radial distance from the center. We find that the IMF becomes steeper at increasing distances from the cluster center (between 30" and 90"), with the number of massive stars (>5Msolar) decreasing from the core to the outskirts of the cluster 5 times more rapidly than the less-massive objects (~=1Msolar). We believe the observed mass segregation to be of a primordial nature rather than dynamical since the age of NGC 330 is 10 times shorter than the expected relaxation time of the cluster. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by AURA for NASA under contract NAS5-26555.

HAZMAT. II. Ultraviolet Variability of Low-mass Stars in the GALEX Archive

NASA Astrophysics Data System (ADS)

Miles, Brittany E.; Shkolnik, Evgenya L.

2017-08-01

The ultraviolet (UV) light from a host star influences a planet’s atmospheric photochemistry and will affect interpretations of exoplanetary spectra from future missions like the James Webb Space Telescope. These effects will be particularly critical in the study of planetary atmospheres around M dwarfs, including Earth-sized planets in the habitable zone. Given the higher activity levels of M dwarfs compared to Sun-like stars, time-resolved UV data are needed for more accurate input conditions for exoplanet atmospheric modeling. The Galaxy Evolution Explorer (GALEX) provides multi-epoch photometric observations in two UV bands: near-ultraviolet (NUV; 1771-2831 Å) and far-ultraviolet (FUV; 1344-1786 Å). Within 30 pc of Earth, there are 357 and 303 M dwarfs in the NUV and FUV bands, respectively, with multiple GALEX observations. Simultaneous NUV and FUV detections exist for 145 stars in both GALEX bands. Our analyses of these data show that low-mass stars are typically more variable in the FUV than the NUV. Median variability increases with later spectral types in the NUV with no clear trend in the FUV. We find evidence that flares increase the FUV flux density far more than the NUV flux density, leading to variable FUV to NUV flux density ratios in the GALEX bandpasses.The ratio of FUV to NUV flux is important for interpreting the presence of atmospheric molecules in planetary atmospheres such as oxygen and methane as a high FUV to NUV ratio may cause false-positive biosignature detections. This ratio of flux density in the GALEX bands spans three orders of magnitude in our sample, from 0.008 to 4.6, and is 1 to 2 orders of magnitude higher than for G dwarfs like the Sun. These results characterize the UV behavior for the largest set of low-mass stars to date.

HAZMAT. II. Ultraviolet Variability of Low-mass Stars in the GALEX Archive

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miles, Brittany E.; Shkolnik, Evgenya L., E-mail: bmiles@ucsc.edu

The ultraviolet (UV) light from a host star influences a planet’s atmospheric photochemistry and will affect interpretations of exoplanetary spectra from future missions like the James Webb Space Telescope . These effects will be particularly critical in the study of planetary atmospheres around M dwarfs, including Earth-sized planets in the habitable zone. Given the higher activity levels of M dwarfs compared to Sun-like stars, time-resolved UV data are needed for more accurate input conditions for exoplanet atmospheric modeling. The Galaxy Evolution Explorer ( GALEX ) provides multi-epoch photometric observations in two UV bands: near-ultraviolet (NUV; 1771–2831 Å) and far-ultraviolet (FUV;more » 1344–1786 Å). Within 30 pc of Earth, there are 357 and 303 M dwarfs in the NUV and FUV bands, respectively, with multiple GALEX observations. Simultaneous NUV and FUV detections exist for 145 stars in both GALEX bands. Our analyses of these data show that low-mass stars are typically more variable in the FUV than the NUV. Median variability increases with later spectral types in the NUV with no clear trend in the FUV. We find evidence that flares increase the FUV flux density far more than the NUV flux density, leading to variable FUV to NUV flux density ratios in the GALEX bandpasses.The ratio of FUV to NUV flux is important for interpreting the presence of atmospheric molecules in planetary atmospheres such as oxygen and methane as a high FUV to NUV ratio may cause false-positive biosignature detections. This ratio of flux density in the GALEX bands spans three orders of magnitude in our sample, from 0.008 to 4.6, and is 1 to 2 orders of magnitude higher than for G dwarfs like the Sun. These results characterize the UV behavior for the largest set of low-mass stars to date.« less

CFBDSIR 2149-0403: young isolated planetary-mass object or high-metallicity low-mass brown dwarf?

NASA Astrophysics Data System (ADS)

Delorme, P.; Dupuy, T.; Gagné, J.; Reylé, C.; Forveille, T.; Liu, M. C.; Artigau, E.; Albert, L.; Delfosse, X.; Allard, F.; Homeier, D.; Malo, L.; Morley, C.; Naud, M. E.; Bonnefoy, M.

2017-06-01

Aims: We conducted a multi-wavelength, multi-instrument observational characterisation of the candidate free-floating planet CFBDSIR J214947.2-040308.9, a late T-dwarf with possible low-gravity features, in order to constrain its physical properties. Methods: We analysed nine hours of X-shooter spectroscopy with signal detectable from 0.8 to 2.3 μm, as well as additional photometry in the mid-infrared using the Spitzer Space Telescope. Combined with a VLT/HAWK-I astrometric parallax, this enabled a full characterisation of the absolute flux from the visible to 5 μm, encompassing more than 90% of the expected energy emitted by such a cool late T-type object. Our analysis of the spectrum also provided the radial velocity and therefore the determination of its full 3D kinematics. Results: While our new spectrum confirms the low gravity and/or high metallicity of CFBDSIR 2149, the parallax and kinematics safely rule out membership to any known young moving group, including AB Doradus. We use the equivalent width of the K I doublet at 1.25 μm as a promising tool to discriminate the effects of low-gravity from the effects of high-metallicity on the emission spectra of cool atmospheres. In the case of CFBDSIR 2149, the observed K I doublet clearly favours the low-gravity solution. Conclusions: CFBDSIR 2149 is therefore a peculiar late-T dwarf that is probably a young, planetary-mass object (2-13 MJup, <500 Myr) possibly similar to the exoplanet 51 Eri b, or perhaps a 2-40 MJup brown dwarf with super-solar metallicity. Based on observations obtained with X-shooter on VLT-UT2 at ESO-Paranal (run 091.D-0723). Based on observations obtained with HAWKI on VLT-UT4 (run 089.C-0952, 090.C-0483, 091.C-0543,092.C-0548,293.C-5019(A) and run 086.C-0655(A)). Based on observations obtained with ISAAC on VLT-UT3 at ESO-Paranal (run 290.C-5083). Based on observation obtained with WIRCam at CFHT (program 2012BF12). Based on Spitzer Space telescope DDT observation (program 10166).

Outbursts by low-mass white dwarfs in symbiotic variables

NASA Technical Reports Server (NTRS)

Sion, Edward M.; Ready, Christian J.

1992-01-01

The high-resolution IUE spectra of the symbiotic variables BF Cygni and EG Andromedae are studied in order to describe the P Cygni-like features of these objects. The 10 high-dispersion IUE spectra are examined for orbital phase-dependent variations in the C IV resonance doublet in terms of velocity and/or structure. One image is found to have a strong He-II absorption feature that coincides in velocity with the C-IV absorption component in P Cygni. The absorbing material for both lines is related to outflow and P Cygni self-absorption near the hot component. The P Cygni profiles do not appear to be related to a red-giant wind nor an expanding circumbinary shell in the in both BF Cyg and EG And. Quasi-static evolutionary model calculations demonstrate an unexpected outburst behavior in response to the assumed accretion. These data are shown to be important for the study of symbiotic systems that contain low-mass white dwarfs.

BANYAN. V. A SYSTEMATIC ALL-SKY SURVEY FOR NEW VERY LATE-TYPE LOW-MASS STARS AND BROWN DWARFS IN NEARBY YOUNG MOVING GROUPS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gagné, Jonathan; Lafrenière, David; Doyon, René

2015-01-10

We present the BANYAN All-Sky Survey (BASS) catalog, consisting of 228 new late-type (M4-L6) candidate members of nearby young moving groups (YMGs) with an expected false-positive rate of ∼13%. This sample includes 79 new candidate young brown dwarfs and 22 planetary-mass objects. These candidates were identified through the first systematic all-sky survey for late-type low-mass stars and brown dwarfs in YMGs. We cross-matched the Two Micron All Sky Survey and AllWISE catalogs outside of the galactic plane to build a sample of 98,970 potential ≥M5 dwarfs in the solar neighborhood and calculated their proper motions with typical precisions of 5-15more » mas yr{sup –1}. We selected highly probable candidate members of several YMGs from this sample using the Bayesian Analysis for Nearby Young AssociatioNs II tool (BANYAN II). We used the most probable statistical distances inferred from BANYAN II to estimate the spectral type and mass of these candidate YMG members. We used this unique sample to show tentative signs of mass segregation in the AB Doradus moving group and the Tucana-Horologium and Columba associations. The BASS sample has already been successful in identifying several new young brown dwarfs in earlier publications, and will be of great interest in studying the initial mass function of YMGs and for the search of exoplanets by direct imaging; the input sample of potential close-by ≥M5 dwarfs will be useful to study the kinematics of low-mass stars and brown dwarfs and search for new proper motion pairs.« less

An Explanation of the Very Low Radio Flux of Young Planet-mass Companions

NASA Astrophysics Data System (ADS)

Wu, Ya-Lin; Close, Laird M.; Eisner, Josh A.; Sheehan, Patrick D.

2017-12-01

We report Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm continuum upper limits for five planetary-mass companions DH Tau B, CT Cha B, GSC 6214-210 B, 1RXS 1609 B, and GQ Lup B. Our survey, together with other ALMA studies, have yielded null results for disks around young planet-mass companions and placed stringent dust mass upper limits, typically less than 0.1 M ⊕, when assuming dust continuum is optically thin. Such low-mass gas/dust content can lead to a disk lifetime estimate (from accretion rates) much shorter than the age of the system. To alleviate this timescale discrepancy, we suggest that disks around wide companions might be very compact and optically thick in order to sustain a few Myr of accretion, yet have very weak (sub)millimeter flux so as to still be elusive to ALMA. Our order-of-magnitude estimate shows that compact optically thick disks might be smaller than 1000 R Jup and only emit ∼μJy of flux in the (sub)millimeter, but their average temperature can be higher than that of circumstellar disks. The high disk temperature could impede satellite formation, but it also suggests that mid- to far-infrared might be more favorable than radio wavelengths to characterize disk properties. Finally, the compact disk size might imply that dynamical encounters between the companion and the star, or any other scatterers in the system, play a role in the formation of planetary-mass companions.

Probing Cloud-Driven Variability on Two of the Youngest, Lowest-Mass Brown Dwarfs in the Solar Neighborhood

NASA Astrophysics Data System (ADS)

Schneider, Adam; Cushing, Michael; Kirkpatrick, J. Davy

2016-08-01

Young, late-type brown dwarfs share many properties with directly imaged giant extrasolar planets. They therefore provide unique testbeds for investigating the physical conditions present in this critical temperature and mass regime. WISEA 1147-2040 and 2MASS 1119-1137, two recently discovered late-type (~L7) brown dwarfs, have both been determined to be members of the ~10 Myr old TW Hya Association (Kellogg et al. 2016, Schneider et al. 2016). Each has an estimated mass of 5-6 MJup, making them two of the youngest and lowest-mass free floating objects yet found in the solar neighborhood. As such, these two planetary mass objects provide unparalleled laboratories for investigating giant planet-like atmospheres far from the contaminating starlight of a host sun. Condensate clouds play a critical role in shaping the emergent spectra of both brown dwarfs and gas giant planets, and can cause photometric variability via their non-uniform spatial distribution. We propose to photometrically monitor WISEA 1147-2040 and 2MASS 1119-1137 in order to search for the presence of cloud-driven variability to 1) investigate the potential trend of low surface gravity with high-amplitude variability in a previously unexplored mass regime and 2) explore the angular momentum evolution of isolated planetary mass objects.

Gyrochronology of Low-mass Stars - Age-Rotation-Activity Relations for Young M Dwarfs

NASA Astrophysics Data System (ADS)

Kidder, Benjamin; Shkolnik, E.; Skiff, B.

2014-01-01

New rotation periods for 34 young <300 Myr), early-M dwarfs within 25 parsecs were measured using photometric data collected with telescopes at Lowell Observatory during 2012 and 2013. An additional 25 rotation periods for members of the same sample were found in the literature. Ages were derived from Hα and X-ray emission, lithium absorption, surface gravity, and kinematic association of members of known young moving groups (YMGs). We compared rotation periods with the estimated ages as well as indicators of magnetic activity, with the intention of strengthening age-rotation-activity relations and assessing the possible use of gyrochronology in young, low-mass stars. We compared ages and rotation periods of our target stars to cluster members spanning 1-600 Myr. Rotation periods at every age exhibit a large scatter, with values typically ranging from 0.2 to 15 days. This suggests that gyrochronology for individual field stars will not be possible without a better understanding of the underlying mechanisms that govern angular momentum evolution. Yet, on average, the data still support the predicted trends for spin-up during contraction and spin-down on the main sequence, with the turnover occurring at around 150 Myr for early Ms. This suggests that rotation period distributions can be helpful in evaluating the ages of coeval groups of stars. Many thanks to the National Science Foundation for their support through the Research Experience for Undergraduates Grant AST- 1004107.

Searching For Low-mass Companions Of Cepheids

NASA Astrophysics Data System (ADS)

Remage Evans, Nancy; Bond, H.; Schaefer, G.; Karovska, M.; Mason, B.; DePasquale, J.; Pillitteri, I.; Guinan, E.; Engle, S.

2011-05-01

The role played by binary and multiple stars in star formation is receiving a great deal of attention, both theoretically and observationally. Two questions under discussion are how wide physical companions can be and how frequently massive stars have low mass companions. An important new observational tool is the development of high resolution imaging, both from space and from the ground (Adaptive Optics and interferometry). We are conducting a snapshot survey of the nearest Cepheids using the Hubble Space Telescope Wide Field Camera 3 (WFC3). The aim is to discover possible resolved low mass companions. Results from this survey will be discussed, including images of Eta Aql. X-ray luminosity can confirm or refute that putative low mass companions are young enough to be physical companions. This project tests the reality of both wide and low mass companions of these intermediate-mass stars.

Searching for intermediate-mass black holes via optical variability

NASA Astrophysics Data System (ADS)

Adler-Levine, Ryan; Moran, Edward C.; Kay, Laura

2018-01-01

A handful of nearby dwarf galaxies with intermediate-mass black holes (IMBHs) in their nuclei display significant optical variability on short timescales. To investigate whether dwarf galaxy AGNs as a class exhibit similar variability, we have monitored a sample of low-mass galaxies that possess spectroscopically confirmed type 1 AGNs. However, because of the variations in seeing, focus, and guiding errors that occur in images taken at different epochs, analyses based on aperture photometry are ineffective. We have thus developed a new method for matching point-spread functions in images that permits use of image subtraction photometry techniques. Applying this method to our photometric data, we have confirmed that several galaxies with IMBHs are indeed variable, which suggests that variability can be used to search for IMBHs in low-mass galaxies whose emission-line properties are ambiguous.

Serum Predictors of Percent Lean Mass in Young Adults.

PubMed

Lustgarten, Michael S; Price, Lori L; Phillips, Edward M; Kirn, Dylan R; Mills, John; Fielding, Roger A

2016-08-01

Lustgarten, MS, Price, LL, Phillips, EM, Kirn, DR, Mills, J, and Fielding, RA. Serum predictors of percent lean mass in young adults. J Strength Cond Res 30(8): 2194-2201, 2016-Elevated lean (skeletal muscle) mass is associated with increased muscle strength and anaerobic exercise performance, whereas low levels of lean mass are associated with insulin resistance and sarcopenia. Therefore, studies aimed at obtaining an improved understanding of mechanisms related to the quantity of lean mass are of interest. Percent lean mass (total lean mass/body weight × 100) in 77 young subjects (18-35 years) was measured with dual-energy x-ray absorptiometry. Twenty analytes and 296 metabolites were evaluated with the use of the standard chemistry screen and mass spectrometry-based metabolomic profiling, respectively. Sex-adjusted multivariable linear regression was used to determine serum analytes and metabolites significantly (p ≤ 0.05 and q ≤ 0.30) associated with the percent lean mass. Two enzymes (alkaline phosphatase and serum glutamate oxaloacetate aminotransferase) and 29 metabolites were found to be significantly associated with the percent lean mass, including metabolites related to microbial metabolism, uremia, inflammation, oxidative stress, branched-chain amino acid metabolism, insulin sensitivity, glycerolipid metabolism, and xenobiotics. Use of sex-adjusted stepwise regression to obtain a final covariate predictor model identified the combination of 5 analytes and metabolites as overall predictors of the percent lean mass (model R = 82.5%). Collectively, these data suggest that a complex interplay of various metabolic processes underlies the maintenance of lean mass in young healthy adults.

The CIDA Variability Survey of Orion OB1. I. The Low-Mass Population of Ori OB1a and 1b

NASA Astrophysics Data System (ADS)

Briceño, Cesar; Calvet, Nuria; Hernández, J.; Vivas, A. K.; Hartmann, Lee; Downes, J. J.; Berlind, Perry

2005-02-01

We present results of a large-scale, multiepoch optical survey of the Orion OB1 association, carried out with the QUEST camera at the Venezuela National Astronomical Observatory. We identify for the first time the widely spread low-mass, young population in the Ori OB1a and OB1b subassociations. Candidate members were picked up by their variability in the V band and position in color-magnitude diagrams. We obtained spectra to confirm membership. In a region spanning ~68 deg2, we found 197 new young stars; of these, 56 are located in the Ori OB1a subassociation and 141 in Ori OB1b. The spatial distribution of the low-mass young stars is spatially coincident with that of the high-mass members but suggests a much sharper edge to the association. Comparison with the spatial extent of molecular gas and extinction maps indicates that the subassociation Ori OB1b is concentrated within a ringlike structure of radius ~2°(~15 pc at 440 pc), centered roughly on the star ɛ Ori in the Orion belt. The ring is apparent in 13CO and corresponds to a region with an extinction AV>=1. The stars exhibiting strong Hα emission, an indicator of active accretion, are found along this ring, whereas the center is populated with weak Hα-emitting stars. In contrast, Ori OB1a is located in a region devoid of gas and dust. We identify a grouping of stars within a ~3 deg2 area located in Ori OB1a, roughly clustered around the B2 star 25 Ori. The Herbig Ae/Be star V346 Ori is also associated with this grouping, which could be an older analog of σ Ori. Using several sets of evolutionary tracks, we find an age of 7-10 Myr for Ori OB1a and of ~4-6 Myr for Ori OB1b, consistent with previous estimates from OB stars. Indicators such as the equivalent width of Hα and near-IR excesses show that the number of accreting low-mass stars decreases sharply between Ori OB1b and Ori OB1a. These results indicate that although a substantial fraction of accreting disks remain at ages ~5 Myr, inner disks are

YOUNG STELLAR CLUSTERS CONTAINING MASSIVE YOUNG STELLAR OBJECTS IN THE VVV SURVEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borissova, J.; Alegría, S. Ramírez; Kurtev, R.

The purpose of this research is to study the connections of the global properties of eight young stellar clusters projected in the Vista Variables in the Via Lactea (VVV) ESO Large Public Survey disk area and their young stellar object (YSO) populations. The analysis is based on the combination of spectroscopic parallax-based reddening and distance determinations with main-sequence and pre-main-sequence ishochrone fitting to determine the basic parameters (reddening, age, distance) of the sample clusters. The lower mass limit estimations show that all clusters are low or intermediate mass (between 110 and 1800  M {sub ⊙}), the slope Γ of themore » obtained present-day mass functions of the clusters is close to the Kroupa initial mass function. The YSOs in the cluster’s surrounding fields are classified using low resolution spectra, spectral energy distribution fits with theoretical predictions, and variability, taking advantage of multi-epoch VVV observations. All spectroscopically confirmed YSOs (except one) are found to be massive (more than 8 M {sub ⊙}). Using VVV and GLIMPSE color–color cuts we have selected a large number of new YSO candidates, which are checked for variability and 57% are found to show at least low-amplitude variations. In few cases it was possible to distinguish between YSO and AGB classifications on the basis of light curves.« less

Spectroscopic Confirmation of Young Planetary-mass Companions on Wide Orbits

NASA Astrophysics Data System (ADS)

Bowler, Brendan P.; Liu, Michael C.; Kraus, Adam L.; Mann, Andrew W.

2014-03-01

We present moderate-resolution (R ~ 4000-5000) near-infrared integral field spectroscopy of the young (1-5 Myr) 6-14 M Jup companions ROXs 42B b and FW Tau b obtained with Keck/OSIRIS and Gemini-North/NIFS. The spectrum of ROXs 42B b exhibits clear signs of low surface gravity common to young L dwarfs, confirming its extreme youth, cool temperature, and low mass. Overall, it closely resembles the free-floating 4-7 M Jup L-type Taurus member 2MASS J04373705+2331080. The companion to FW Tau AB is more enigmatic. Our optical and near-infrared spectra show strong evidence of outflow activity and disk accretion in the form of line emission from [S II], [O I], Hα, Ca II, [Fe II], Paβ, and H2. The molecular hydrogen emission is spatially resolved as a single lobe that stretches ≈0.''1 (15 AU). Although the extended emission is not kinematically resolved in our data, its morphology resembles shock-excited H2 jets primarily seen in young Class 0 and Class I sources. The near-infrared continuum of FW Tau b is mostly flat and lacks the deep absorption features expected for a cool, late-type object. This may be a result of accretion-induced veiling, especially in light of its strong and sustained Hα emission (EW(Hα) >~ 290 Å). Alternatively, FW Tau b may be a slightly warmer (M5-M8) accreting low-mass star or brown dwarf (0.03-0.15 M ⊙) with an edge-on disk. Regardless, its young evolutionary stage is in stark contrast to its Class III host FW Tau AB, indicating a more rapid disk clearing timescale for the host binary system than for its wide companion. Finally, we present near-infrared spectra of the young (~2-10 Myr) low-mass (12-15 M Jup) companions GSC 6214-210 B and SR 12 C and find they best resemble low-gravity M9.5 and M9 substellar templates. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National

Detection of X-ray emission from the young low-mass star Rossiter 137B

NASA Technical Reports Server (NTRS)

Vilhu, O.; Linsky, J. L.

1987-01-01

Rst 137B, a close M-dwarf companion to the active K-star HD 36705, has been detected in a High Resolution Image in the Einstein Observatory Archive. The X-ray surface fluxes (0.2-4 keV) from both stars are close to the empirical saturation level, F(x)/F(bol) of about 0.001, defined by rapid rotators and very young stars. This supports the earlier results of the youthfulness of the system. This young couple is an excellent subject for studies of dependence of early evolution on stellar mass. Rst 137B is one of the latest spectral types and thus lowest-mass premain-sequence stars yet detected as an X-ray source.

Constraints on the spin evolution of young planetary-mass companions

NASA Astrophysics Data System (ADS)

Bryan, Marta L.; Benneke, Björn; Knutson, Heather A.; Batygin, Konstantin; Bowler, Brendan P.

2018-02-01

Surveys of young star-forming regions have discovered a growing population of planetary-mass (<13 MJup) companions around young stars1. There is an ongoing debate as to whether these companions formed like planets (that is, from the circumstellar disk)2, or if they represent the low-mass tail of the star-formation process3. In this study, we utilize high-resolution spectroscopy to measure rotation rates of three young (2-300 Myr) planetary-mass companions and combine these measurements with published rotation rates for two additional companions4,5 to provide a picture of the spin distribution of these objects. We compare this distribution to complementary rotation-rate measurements for six brown dwarfs with masses <20 MJup, and show that these distributions are indistinguishable. This suggests that either these two populations formed via the same mechanism, or that processes regulating rotation rates are independent of formation mechanism. We find that rotation rates for both populations are well below their break-up velocities and do not evolve significantly during the first few hundred million years after the end of accretion. This suggests that rotation rates are set during the late stages of accretion, possibly by interactions with a circumplanetary disk. This result has important implications for our understanding of the processes regulating the angular momentum evolution of young planetary-mass objects, and of the physics of gas accretion and disk coupling in the planetary-mass regime.

2MASS J11151597+1937266: A Young, Dusty, Isolated, Planetary-mass Object with a Potential Wide Stellar Companion

NASA Astrophysics Data System (ADS)

Theissen, Christopher A.; Burgasser, Adam J.; Bardalez Gagliuffi, Daniella C.; Hardegree-Ullman, Kevin K.; Gagné, Jonathan; Schmidt, Sarah J.; West, Andrew A.

2018-01-01

We present 2MASS J11151597+1937266, a recently identified low-surface-gravity L dwarf, classified as an L2γ based on Sloan Digital Sky Survey optical spectroscopy. We confirm this spectral type with near-infrared spectroscopy, which provides further evidence that 2MASS J11151597+1937266 is a low-surface-gravity L dwarf. This object also shows significant excess mid-infrared flux, indicative of circumstellar material; and its strong Hα emission (EWHα = 560 ± 82 Å) is an indicator of enhanced magnetic activity or weak accretion. Comparison of its spectral energy distribution to model photospheres yields an effective temperature of {1724}-38+184 {{K}}. We also provide a revised distance estimate of 37 ± 6 pc using a spectral type–luminosity relationship for low-surface-gravity objects. The three-dimensional galactic velocities and positions of 2MASS J11151597+1937266 do not match any known young association or moving group. Assuming a probable age in the range of 5–45 Myr, the model-dependent estimated mass of this object is between 7 and 21 M Jup, making it a potentially isolated planetary-mass object. We also identify a candidate co-moving, young stellar companion, 2MASS J11131089+2110086.

The Young L Dwarf 2MASS J11193254-1137466 Is a Planetary-mass Binary

NASA Astrophysics Data System (ADS)

Best, William M. J.; Liu, Michael C.; Dupuy, Trent J.; Magnier, Eugene A.

2017-07-01

We have discovered that the extremely red, low-gravity L7 dwarf 2MASS J11193254-1137466 is a 0.″14 (3.6 au) binary using Keck laser guide star adaptive optics imaging. 2MASS J11193254-1137466 has previously been identified as a likely member of the TW Hydrae Association (TWA). Using our updated photometric distance and proper motion, a kinematic analysis based on the BANYAN II model gives an 82% probability of TWA membership. At TWA’s 10 ± 3 Myr age and using hot-start evolutionary models, 2MASS J11193254-1137466AB is a pair of {3.7}-0.9+1.2 {M}{Jup} brown dwarfs, making it the lowest-mass binary discovered to date. We estimate an orbital period of {90}-50+80 years. One component is marginally brighter in K band but fainter in J band, making this a probable flux-reversal binary, the first discovered with such a young age. We also imaged the spectrally similar TWA L7 dwarf WISEA J114724.10-204021.3 with Keck and found no sign of binarity. Our evolutionary model-derived {T}{eff} estimate for WISEA J114724.10-204021.3 is ≈230 K higher than for 2MASS J11193254-1137466AB, at odds with the spectral similarity of the two objects. This discrepancy suggests that WISEA J114724.10-204021.3 may actually be a tight binary with masses and temperatures very similar to 2MASS J11193254-1137466AB, or further supporting the idea that near-infrared spectra of young ultracool dwarfs are shaped by factors other than temperature and gravity. 2MASS J11193254-1137466AB will be an essential benchmark for testing evolutionary and atmospheric models in the young planetary-mass regime.

Spitzer Light Curves of the Young, Planetary-mass TW Hya Members 2MASS J11193254–1137466AB and WISEA J114724.10–204021.3

NASA Astrophysics Data System (ADS)

Schneider, Adam C.; Hardegree-Ullman, Kevin K.; Cushing, Michael C.; Kirkpatrick, J. Davy; Shkolnik, Evgenya L.

2018-06-01

We present Spitzer Space Telescope time-series photometry at 3.6 and 4.5 μm of 2MASS J11193254‑1137466AB and WISEA J114724.10‑204021.3, two planetary-mass, late-type (∼L7) brown dwarf members of the ∼10 Myr old TW Hya Association. These observations were taken in order to investigate whether or not a tentative trend of increasing variability amplitude with decreasing surface gravity seen for L3–L5.5 dwarfs extends to later-L spectral types and to explore the angular momentum evolution of low-mass objects. We examine each light curve for variability and find a rotation period of 19.39+0.33 ‑0.28 hr and semi-amplitudes of 0.798+0.081 ‑0.083% at 3.6 μm and 1.108+0.093 ‑0.094% at 4.5 μm for WISEA J114724.10‑204021.3. For 2MASS J11193254‑1137466AB, we find a single period of 3.02+0.04 ‑0.03 hr with semi-amplitudes of 0.230+0.036 ‑0.035% at 3.6 μm and 0.453 ± 0.037% at 4.5 μm, which we find is possibly due to the rotation of one component of the binary. Combining our results with 12 other late-type L dwarfs observed with Spitzer from the literature, we find no significant differences between the 3.6 μm amplitudes of low surface gravity and field gravity late-type L brown dwarfs at Spitzer wavelengths, and find tentative evidence (75% confidence) of higher amplitude variability at 4.5 μm for young, late-type Ls. We also find a median rotation period of young brown dwarfs (10–300 Myr) of ∼10 hr, more than twice the value of the median rotation period of field-age brown dwarfs (∼4 hr), a clear signature of brown dwarf rotational evolution.

HIGHLY VARIABLE YOUNG MASSIVE STARS IN ATLASGAL CLUMPS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, M. S. N.; Contreras Peña, C.; Lucas, P. W.

High-amplitude variability in young stellar objects (YSOs) is usually associated with episodic accretion events. It has not been observed so far in massive YSOs. Here, the high-amplitude variable star sample of Contreras Peña et al. has been used to search for highly variable (Δ K  ≥ 1 mag) sources coinciding with dense clumps mapped using the 850  μ m continuum emission by the ATLASGAL survey. A total of 18 variable sources are centered on the submillimeter clump peaks and coincide (<1″) with a 24  μ m point or compact (<10″) source. Of these 18 sources, 13 can be fit by YSOmore » models. The 13 variable YSOs (VYSOs) have luminosities of ∼10{sup 3} L {sub ⊙}, an average mass of 8  M {sub ⊙}, and a range of ages up to 10{sup 6} yr. A total of 11 of these 13 VYSOs are located in the midst of infrared dark clouds. Nine of the 13 sources have Δ K  > 2 mag, significantly higher compared to the mean variability of the entire VVV sample. The light curves of these objects sampled between 2010 and 2015 display rising, declining, or quasi-periodic behavior but no clear periodicity. Light-curve analysis using the Plavchan method shows that the most prominent phased signals have periods of a few hundred days. The nature and timescale of variations found in 6.7 Ghz methanol maser emission in massive stars are similar to that of the VYSO light curves. We argue that the origin of the observed variability is episodic accretion. We suggest that the timescale of a few hundred days may represent the frequency at which a spiraling disk feeds dense gas to the young massive star.« less

Gemini Spectroscopic Survey of Young Intermediate-Mass Star-Forming Regions

NASA Astrophysics Data System (ADS)

Lundquist, Michael; Kobulnicky, Henry

2018-01-01

The majority of stars form in embedded clusters. Current research into star formation has focused on either high-mass star-forming regions or low-mass star-forming regions. We present the results from a Gemini spectroscopic survey of young intermediate-mass star-forming regions. These are star forming regions selected to produce stars up to but not exceeding 8 solar masses. We obtained spectra of these regions with GNIRS on Gemini North and Flamingos-2 on Gemini South. We also combine this with near-infrared imaging from 2MASS, UKIDSS, and VVV to study the stellar content.

X-rays from Young Low-Mass Stars: Inhospitable Habitable Zones?

NASA Astrophysics Data System (ADS)

Kastner, Joel

2016-09-01

The irradiation of protoplanetary disks by high-energy radiation from magnetic and accretion activity at low-mass, pre-MS stars likely plays an essential role in regulating exoplanet formation around such stars. To provide the X-ray data necessary to address the problem of the dissipation of protoplanetary disks around the lowest-mass stars, we propose a survey of a sample of previously established and newly-discovered mid- to late-type M type members of the nearby TW Hya Association (age 8 Myr), most of which were the subjects of our recent ALMA survey to detect dusty disks. The combined Chandra and ALMA survey of the TWA will provide a unique resource with which to investigate X-ray-induced photoevaporation of disks orbiting very low-mass stars and massive brown dwarfs.

Deconstructed transverse mass variables

DOE PAGES

Ismail, Ahmed; Schwienhorst, Reinhard; Virzi, Joseph S.; ...

2015-04-02

Traditional searches for R-parity conserving natural supersymmetry (SUSY) require large transverse mass and missing energy cuts to separate the signal from large backgrounds. SUSY models with compressed spectra inherently produce signal events with small amounts of missing energy that are hard to explore. We use this difficulty to motivate the construction of "deconstructed" transverse mass variables which are designed preserve information on both the norm and direction of the missing momentum. Here, we demonstrate the effectiveness of these variables in searches for the pair production of supersymmetric top-quark partners which subsequently decay into a final state with an isolated lepton,more » jets and missing energy. We show that the use of deconstructed transverse mass variables extends the accessible compressed spectra parameter space beyond the region probed by traditional methods. The parameter space can further be expanded to neutralino masses that are larger than the difference between the stop and top masses. In addition, we also discuss how these variables allow for novel searches of single stop production, in order to directly probe unconstrained stealth stops in the small stop-and neutralino-mass regime. We also demonstrate the utility of these variables for generic gluino and stop searches in all-hadronic final states. Overall, we demonstrate that deconstructed transverse variables are essential to any search wanting to maximize signal separation from the background when the signal has undetected particles in the final state.« less

Variability of Massive Young Stellar Objects in Cygnus-X

NASA Astrophysics Data System (ADS)

Thomas, Nancy H.; Hora, J. L.; Smith, H. A.

2013-01-01

Young stellar objects (YSOs) are stars in the process of formation. Several recent investigations have shown a high rate of photometric variability in YSOs at near- and mid-infrared wavelengths. Theoretical models for the formation of massive stars (1-10 solar masses) remain highly idealized, and little is known about the mechanisms that produce the variability. An ongoing Spitzer Space Telescope program is studying massive star formation in the Cygnus-X region. In conjunction with the Spitzer observations, we have conducted a ground-based near-infrared observing program of the Cygnus-X DR21 field using PAIRITEL, the automated infrared telescope at Whipple Observatory. Using the Stetson index for variability, we identified variable objects and a number of variable YSOs in our time-series PAIRITEL data of DR21. We have searched for periodicity among our variable objects using the Lomb-Scargle algorithm, and identified periodic variable objects with an average period of 8.07 days. Characterization of these variable and periodic objects will help constrain models of star formation present. This work is supported in part by the NSF REU and DOD ASSURE programs under NSF grant no. 0754568 and by the Smithsonian Institution.

Planets around Low-mass Stars (PALMS). I. A Substellar Companion to the Young M Dwarf 1RXS J235133.3+312720

NASA Astrophysics Data System (ADS)

Bowler, Brendan P.; Liu, Michael C.; Shkolnik, Evgenya L.; Dupuy, Trent J.; Cieza, Lucas A.; Kraus, Adam L.; Tamura, Motohide

2012-07-01

We report the discovery of a brown dwarf companion to the young M dwarf 1RXS J235133.3+312720 as part of a high contrast imaging search for planets around nearby young low-mass stars with Keck-II/NIRC2 and Subaru/HiCIAO. The 2farcs4 (~120 AU) pair is confirmed to be comoving from two epochs of high-resolution imaging. Follow-up low- and moderate-resolution near-infrared spectroscopy of 1RXS J2351+3127 B with IRTF/SpeX and Keck-II/OSIRIS reveals a spectral type of L0+2 -1. The M2 primary star 1RXS J2351+3127 A exhibits X-ray and UV activity levels comparable to young moving group members with ages of ~10-100 Myr. UVW kinematics based the measured radial velocity of the primary and the system's photometric distance (50 ± 10 pc) indicate it is likely a member of the ~50-150 Myr AB Dor moving group. The near-infrared spectrum of 1RXS J2351+3127 B does not exhibit obvious signs of youth, but its H-band morphology shows subtle hints of intermediate surface gravity. The spectrum is also an excellent match to the ~200 Myr M9 brown dwarf LP 944-20. Assuming an age of 50-150 Myr, evolutionary models imply a mass of 32 ± 6 M Jup for the companion, making 1RXS J2351+3127 B the second lowest-mass member of the AB Dor moving group after the L4 companion CD-35 2722 B and one of the few benchmark brown dwarfs known at young ages. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Relationship between Young Children's Habitual Computer Use and Influencing Variables on Socio-Emotional Development

ERIC Educational Resources Information Center

Seo, Hyun Ah; Chun, Hui Young; Jwa, Seung Hwa; Choi, Mi Hyun

2011-01-01

This study investigates the relationship between young children's habitual computer use and influencing variables on socio-emotional development. The participants were 179 five-year-old children. The Internet Addiction Scale for Young Children (IASYC) was used to identify children with high and low levels of habituation to computer use. The data…

Rapid X-ray variability properties during the unusual very hard state in neutron-star low-mass X-ray binaries

NASA Astrophysics Data System (ADS)

Wijnands, R.; Parikh, A. S.; Altamirano, D.; Homan, J.; Degenaar, N.

2017-11-01

Here, we study the rapid X-ray variability (using XMM-Newton observations) of three neutron-star low-mass X-ray binaries (1RXS J180408.9-342058, EXO 1745-248 and IGR J18245-2452) during their recently proposed very hard spectral state. All our systems exhibit a strong to very strong noise component in their power density spectra (rms amplitudes ranging from 34 per cent to 102 per cent) with very low characteristic frequencies (as low as 0.01 Hz). These properties are more extreme than what is commonly observed in the canonical hard state of neutron-star low-mass X-ray binaries observed at X-ray luminosities similar to those we observe from our sources. This suggests that indeed the very hard state is a spectral-timing state distinct from the hard state, although we argue that the variability behaviour of IGR J18245-2452 is very extreme and possibly this source was in a very unusual state. We also compare our results with the rapid X-ray variability of the accreting millisecond X-ray pulsars IGR J00291+5934 and Swift J0911.9-6452 (also using XMM-Newton data) for which previously similar variability phenomena were observed. Although their energy spectra (as observed using the Swift X-ray telescope) were not necessarily as hard (i.e. for Swift J0911.9-6452) as for our other three sources, we conclude that likely both sources were also in very similar state during their XMM-Newton observations. This suggests that different sources that are found in this new state might exhibit different spectral hardness and one has to study both the spectral and the rapid variability to identify this unusual state.

Ultraviolet emission lines in young low-mass galaxies at z ≃ 2: physical properties and implications for studies at z > 7

NASA Astrophysics Data System (ADS)

Stark, Daniel P.; Richard, Johan; Siana, Brian; Charlot, Stéphane; Freeman, William R.; Gutkin, Julia; Wofford, Aida; Robertson, Brant; Amanullah, Rahman; Watson, Darach; Milvang-Jensen, Bo

2014-12-01

We present deep spectroscopy of 17 very low mass (M⋆ ≃ 2.0 × 106-1.4 × 109 M⊙) and low luminosity (MUV ≃ -13.7 to -19.9) gravitationally lensed galaxies in the redshift range z ≃ 1.5-3.0. Deep rest-frame ultraviolet spectra reveal large equivalent width emission from numerous emission lines (N IV], O III], C IV, Si III], C III]) which are rarely seen in individual spectra of more massive star-forming galaxies. C III] is detected in 16 of 17 low-mass star-forming systems with rest-frame equivalent widths as large as 13.5 Å. Nebular C IV emission is present in the most extreme C III] emitters, requiring an ionizing source capable of producing a substantial component of photons with energies in excess of 47.9 eV. Photoionization models support a picture whereby the large equivalent widths are driven by the increased electron temperature and enhanced ionizing output arising from metal-poor gas and stars (0.04-0.13 Z⊙), young stellar populations (6-50 Myr), and large ionization parameters (log U = -2.16 to -1.84). The young ages implied by the emission lines and continuum spectral energy distributions (SEDs) indicate that the extreme line emitters in our sample are in the midst of a significant upturn in their star formation activity. The low stellar masses, blue UV colours, and large specific star formation rates of our sample are similar to those of typical z ≳ 6 galaxies. Given the strong attenuation of Lyα in z ≳ 6 galaxies, we suggest that C III] is likely to provide our best probe of early star-forming galaxies with ground-based spectrographs and one off the most efficient means of confirming z ≳ 10 galaxies with the James Webb Space Telescope.

Hazardous Early Days In (and Beyond) the Habitable Zones Around Ultra-Low-Mass Stars

NASA Astrophysics Data System (ADS)

Kastner, Joel

Although a majority of stars in the solar neighborhood are of mid- to late-M type, the magnetically-induced coronal (X-ray) and chromospheric (UV, H-alpha) activity of such stars remain essentially unexplored for the important age range 10-100 Myr. Such information on high-energy processes associated with young M stars would provide much-needed constraints on models of the effects of stellar irradiation on the physics and chemistry of planet-forming disks and newborn planets. In addition, X-ray and UV observations of ultra-low-mass young stars can serve to probe the (presently ill-defined) spectral type boundary that determines which very low-mass objects will eventually become M stars -- as opposed to brown dwarfs (BDs) -- following their pre-main sequence evolutionary stages. Via ADAP support, we have developed the GALEX Nearby Young Star Search (GALNYSS), a search method that combines GALEX, 2MASS, WISE and proper motion catalog information to identify nearby, young, lowmass stars. We have applied this method to identify ~2000 candidate young (10-100 Myr), low-mass (M-type) stars within 150 pc. These GALNYSS-identified young star candidates are distributed over the entire GALEX-covered sky, and their spectral types peak in the M3-4 range; followup optical spectroscopic work is ongoing (Rodriguez et al. 2013, ApJ, 774, 101). We now propose an ADA program to determine the X-ray properties of representative stars among these GALNYSS candidates, so as to confirm their youth and investigate the early evolution of coronal activity near the low-mass star/BD boundary and the effects of such activity on planet formation. Specifically, we will exploit the presence in the HEASARC archives of XMM-Newton and (to a lesser extent) Chandra X-ray Observatory data for a few dozen GALNYSS candidates that have been observed serendipitously by one or both of these space observatories. The proposed ADA program will yield the full reduction and analysis of these as-yet unexplored data

Relationship of low lean body mass with body weight increase until one year of age and current lifestyles in Japanese young women.

PubMed

Miyamoto, Shoji; Murotani, Kenta; Yanagawa, Takashi; Kato, Atsushi; Matsunaga, Satoshi

2010-06-01

To investigate factors affecting the low lean body mass (LBM) of young women, we focused on the increase in body weight until one year of age and current lifestyles. In 442 young women, the increase in body weight from birth until one year of age, breast-feeding method in infancy, current physique index and body composition, and physique and lifestyles were investigated using a questionnaire. Subjects with an LBM percentile of less than 33.3 (less than 36.8 kg) were classified as having a low LBM (n = 150), and those with a 33.3 or higher LBM percentile as the control (n = 293). Based on body weight changes from birth to days 3 and 7, the subjects were divided into a rapid weight gain group and two non-rapid weight gain groups (groups 1-3). To analyze factors involved in a low LBM, multivariate analysis using a logistic model was employed. The prevalence of a low LBM in the rapid weight gain group was 0.41 times higher than in the others. The prevalence of a low LBM with a low birth weight was 0.58 times higher, indicating that a low birth weight is likely to result in a low LBM. Regarding the lifestyles, the prevalence of a low LBM in subjects with a current breakfasting habit was 0.60 times higher than in those without one. These findings suggest that the thinness of young women characterized by a low LBM is associated with the increase in body weight until one year of age and current lifestyles.

Mass transfer cycles in cataclysmic variables

NASA Technical Reports Server (NTRS)

King, A. R.; Frank, J.; Kolb, U.; Ritter, H.

1995-01-01

It is well known that in cataclysmic variables the mass transfer rate must fluctuate about the evolutionary mean on timescales too long to be directly observable. We show that limit-cycle behavior can occur if the radius change of the secondary star is sensitive to the instantaneous mass transfer rate. The only reasonable way in which such a dependence can arise is through irradiation of this star by the accreting component. The system oscillates between high states, in which irradiation causes slow expansion of the secondary and drives an elevated transfer rate, and low states, in which this star contracts.

Voluntary reduction of force variability via modulation of low-frequency oscillations.

PubMed

Park, Seoung Hoon; Casamento-Moran, Agostina; Yacoubi, Basma; Christou, Evangelos A

2017-09-01

Visual feedback can influence the force output by changing the power in frequencies below 1 Hz. However, it remains unknown whether visual guidance can help an individual reduce force variability voluntarily. The purpose of this study, therefore, was to determine whether an individual can voluntarily reduce force variability during constant contractions with visual guidance, and whether this reduction is associated with a decrease in the power of low-frequency oscillations (0-1 Hz) in force and muscle activity. Twenty young adults (27.6 ± 3.4 years) matched a force target of 15% MVC (maximal voluntary contraction) with ankle dorsiflexion. Participants performed six visually unrestricted contractions, from which we selected the trial with the least variability. Following, participants performed six visually guided contractions and were encouraged to reduce their force variability within two guidelines (±1 SD of the least variable unrestricted trial). Participants decreased the SD of force by 45% (P < 0.001) during the guided condition, without changing mean force (P > 0.2). The decrease in force variability was associated with decreased low-frequency oscillations (0-1 Hz) in force (R 2  = 0.59), which was associated with decreased low-frequency oscillations in EMG bursts (R 2  = 0.35). The reduction in low-frequency oscillations in EMG burst was positively associated with power in the interference EMG from 35 to 60 Hz (R 2  = 0.47). In conclusion, voluntary reduction of force variability is associated with decreased low-frequency oscillations in EMG bursts and consequently force output. We provide novel evidence that visual guidance allows healthy young adults to reduce force variability voluntarily likely by adjusting the low-frequency oscillations in the neural drive.

The influence of body mass index and outdoor temperature on the autonomic response to eating in healthy young Japanese women.

PubMed

Okada, Masahiro; Kakehashi, Masayuki

2014-01-01

The influences of body weight and air temperature on the autonomic response to food intake have not been clarified. We measured heart rate variability before and after lunch, as well as the effects of outdoor temperature and increased body mass index (BMI), in healthy young Japanese women. We studied 55 healthy young female university students. Heart rate variability was measured before lunch, immediately after lunch, 30 min after lunch, and 1 h after lunch to determine any correlations between heart rate variability, outdoor temperature, and BMI. In addition, multiple regression analysis was performed to elucidate the relationship between heart rate variability and outdoor temperature before and after lunch. A simple slope test was conducted to show the relationship between the low-to-high frequency ratio (1 h after lunch) and outdoor temperature. Subjects were divided into a low BMI group (range: 16.6-20.3) and a high BMI group (range: 20.4-32.9). The very low frequency component of heart rate variability, an index of thermoregulatory vasomotor control exerted by the sympathetic nervous system, was significantly diminished after lunch in the high BMI group (P < 0.01). A significant decrease in the low-to-high frequency (LF/HF) ratio, which represents the balance between the parasympathetic and sympathetic nervous systems, was evident in the low BMI group after lunch, indicating parasympathetic system dominance (P = 0.001). In addition, a significant association was found between the LF/HF ratio and outdoor temperature after lunch with a lower BMI (P = 0.002), but this association disappeared with higher BMIs. Autonomic responses to eating showed clear differences according to BMI, indicating that the sensitivity of the autonomic nervous system may change with increases in BMI.

Association of low back pain with muscle stiffness and muscle mass of the lumbar back muscles, and sagittal spinal alignment in young and middle-aged medical workers.

PubMed

Masaki, Mitsuhiro; Aoyama, Tomoki; Murakami, Takashi; Yanase, Ko; Ji, Xiang; Tateuchi, Hiroshige; Ichihashi, Noriaki

2017-11-01

Muscle stiffness of the lumbar back muscles in low back pain (LBP) patients has not been clearly elucidated because quantitative assessment of the stiffness of individual muscles was conventionally difficult. This study aimed to examine the association of LBP with muscle stiffness assessed using ultrasonic shear wave elastography (SWE) and muscle mass of the lumbar back muscle, and spinal alignment in young and middle-aged medical workers. The study comprised 23 asymptomatic medical workers [control (CTR) group] and 9 medical workers with LBP (LBP group). Muscle stiffness and mass of the lumbar back muscles (lumbar erector spinae, multifidus, and quadratus lumborum) in the prone position were measured using ultrasonic SWE. Sagittal spinal alignment in the standing and prone positions was measured using a Spinal Mouse. The association with LBP was investigated by multiple logistic regression analysis with a forward selection method. The analysis was conducted using the shear elastic modulus and muscle thickness of the lumbar back muscles, and spinal alignment, age, body height, body weight, and sex as independent variables. Multiple logistic regression analysis showed that muscle stiffness of the lumbar multifidus muscle and body height were significant and independent determinants of LBP, but that muscle mass and spinal alignment were not. Muscle stiffness of the lumbar multifidus muscle in the LBP group was significantly higher than that in the CTR group. The results of this study suggest that LBP is associated with muscle stiffness of the lumbar multifidus muscle in young and middle-aged medical workers. Copyright © 2017 Elsevier Ltd. All rights reserved.

On the fast quenching of young low-mass galaxies up to z ˜ 0.6. New spotlight on the lead role of environment

NASA Astrophysics Data System (ADS)

Moutard, Thibaud; Sawicki, Marcin; Arnouts, Stéphane; Golob, Anneya; Malavasi, Nicola; Adami, Christophe; Coupon, Jean; Ilbert, Olivier

2018-06-01

We investigate the connection between environment and the different quenching channels that galaxies are prone to follow in the rest-frame NUVrK colour diagram, as identified by Moutard et al. (2016b). Namely, the fast quenching channel followed by young low-mass galaxies and the slow quenching channel followed by old high-mass ones. We make use of the >22 deg2 covered the VIPERS Multi-Lambda Survey (VIPERS-MLS) to select a galaxy sample complete down to stellar masses of M* > 109.4M⊙ up to z ˜ 0.65 (M* > 108.8M⊙ up to z ˜ 0.5) and including 33,500 (43,000) quiescent galaxies properly selected at 0.2 < z < 0.65, while being characterized by reliable photometric redshifts (σδz/(1 + z) ≤ 0.04) that we use to measure galaxy local densities. We find that (1) the quiescence of low-mass [M* ≤ 109.7M⊙] galaxies requires a strong increase of the local density, which confirms the lead role played by environment in their fast quenching and, therefore, confirms that the low-mass upturn observed in the stellar mass function of quiescent galaxies is due to environmental quenching. We also observe that (2) the reservoir of low-mass star-forming galaxies located in very dense regions (prone to environmental quenching) has grown between z ˜ 0.6 and z ˜ 0.4 whilst the share of low-mass quiescent galaxies (expected to being environmentally quenched) may have simultaneously increased, which would plead for a rising importance of environmental quenching with cosmic time, compared to mass quenching. We finally discuss the composite picture of such environmental quenching of low-mass galaxies and, in particular, how this picture may be consistent with a delayed-then-rapid quenching scenario.

The Planets Around Low-Mass Stars (PALMS) Direct Imaging Survey

NASA Astrophysics Data System (ADS)

Bowler, Brendan P.; Liu, M. C.; Shkolnik, E.; Mann, A.; Tamura, M.

2013-01-01

Direct imaging is the only method to study the outer architecture (>10 AU) of extrasolar planetary systems in a targeted fashion. Previous imaging surveys have primarily focused on intermediate- and high-mass stars because of the relative dearth of known nearby young M dwarfs. As a result, even though M dwarfs make up 70% of stars in our galaxy, there are few constraints on the population of giant planets at moderate separations (10-100 AU) in this stellar mass regime. We present results from an ongoing high-contrast adaptive optics imaging survey targeting newly identified nearby (<35 pc) young (<300 Myr) M dwarfs with Keck-2/NIRC2 and Subaru/HiCIAO. We have already discovered four young brown dwarf companions with masses between 30-70 Mjup; two of these are members of the ~120 Myr AB Dor moving group, and another one will yield a dynamical mass in the near future. Follow-up optical and near-infrared spectroscopy of these companions reveal spectral types of late-M to early-L and spectroscopic indicators of youth such as angular H-band morphologies, weak J-band alkali lines, and Li absorption and Halpha emission in one target. Altogether our survey is sensitive to planet masses a few times that of Jupiter at separations down to ~10 AU. With a sample size of roughly 80 single M dwarfs, this program represents the deepest and most extensive imaging search for planets around young low-mass stars to date.

Companions and Environments of Low-Mass Stars: From Star-Forming Regions to the Field

NASA Astrophysics Data System (ADS)

Ward-Duong, Kimberly; Patience, Jenny; De Rosa, Robert J.; Bulger, Joanna; Rajan, Abhijith; Goodwin, Simon; Parker, Richard J.; McCarthy, Donald W.; Kulesa, Craig; van der Plas, Gerrit; Menard, Francois; Pinte, Christophe; Jackson, Alan Patrick; Bryden, Geoffrey; Turner, Neal J.; Harvey, Paul M.; Hales, Antonio

2017-01-01

We present results from two studies probing the multiplicity and environmental properties of low-mass stars: (1) The MinMs (M-dwarfs in Multiples) Survey, a large, volume-limited survey of 245 field M-dwarfs within 15 pc, and (2) the TBOSS (Taurus Boundary of Stellar/Substellar) Survey, an ongoing study of disk properties for the lowest-mass members within the Taurus star-forming region. The MinMs Survey provides new measurements of the companion star fraction, separation distribution, and mass ratio distribution for the nearest K7-M6 dwarfs, utilizing a combination of high-resolution adaptive optics imaging and digitized widefield archival plates to cover an unprecedented separation range of ~1-10,000 AU. Within these data, we also identify companions below the stellar/brown dwarf boundary, enabling characterization of the substellar companion population to low-mass field stars. For the much younger population in Taurus, we present results from ALMA Band 7 continuum observations of low-mass stellar and substellar Class II objects, spanning spectral types from M4-M7.75. The sub-millimeter detections of these disks provide key estimates of the dust mass in small grains, which is then assessed within the context of region age, environment, and viability for planet formation. This young population also includes a number of interesting young binary systems. Covering both young (1-2 Myr) and old (>5 Gyr) populations of low-mass stars, the results from these studies provide benchmark measurements on the population statistics of low-mass field stars, and on the early protoplanetary environments of their younger M-star counterparts.

Mass Accretion Processes in Young Stellar Objects: Role of Intense Flaring Activity

NASA Astrophysics Data System (ADS)

Orlando, Salvatore; Reale, Fabio; Peres, Giovanni; Mignone, Andrea

2014-11-01

According to the magnetospheric accretion scenario, young low-mass stars are surrounded by circumstellar disks which they interact with through accretion of mass. The accretion builds up the star to its final mass and is also believed to power the mass outflows, which may in turn have a signicant role in removing the excess angular momentum from the star-disk system. Although the process of mass accretion is a critical aspect of star formation, some of its mechanisms are still to be fully understood. On the other hand, strong flaring activity is a common feature of young stellar objects (YSOs). In the Sun, such events give rise to perturbations of the interplanetary medium. Similar but more energetic phenomena occur in YSOs and may influence the circumstellar environment. In fact, a recent study has shown that an intense flaring activity close to the disk may strongly perturb the stability of circumstellar disks, thus inducing mass accretion episodes (Orlando et al. 2011). Here we review the main results obtained in the field and the future perspectives.

The young, tight, and low-mass binary TWA22AB: a new calibrator for evolutionary models?. Orbit, spectral types, and temperature

NASA Astrophysics Data System (ADS)

Bonnefoy, M.; Chauvin, G.; Dumas, C.; Lagrange, A.-M.; Beust, H.; Desort, M.; Teixeira, R.; Ducourant, C.; Beuzit, J.-L.; Song, I.

2009-11-01

Context: Tight binaries discovered in young, nearby associations are ideal targets for providing dynamical mass measurements to test the physics of evolutionary models at young ages and very low masses. Aims: We report the binarity of TWA22 for the first time. We aim at monitoring the orbit of this young and tight system to determine its total dynamical mass using an accurate distance determination. We also intend to characterize the physical properties (luminosity, effective temperature, and surface gravity) of each component based on near-infrared photometric and spectroscopic observations. Methods: We used the adaptive-optics assisted imager NACO to resolve the components, to monitor the complete orbit and to obtain the relative near-infrared photometry of TWA22 AB. The adaptive-optics assisted integral field spectrometer SINFONI was also used to obtain medium-resolution (Rλ=1500-2000) spectra in JHK bands. Comparison with empirical and synthetic librairies were necessary for deriving the spectral type, the effective temperature, and the surface gravity for each component of the system. Results: Based on an accurate trigonometric distance (17.5 ± 0.2 pc) determination, we infer a total dynamical mass of 220 ± 21 MJup for the system. From the complete set of spectra, we find an effective temperature T_eff=2900+200-200 K for TWA22 A and T_eff=2900+200-100 K for TWA22 B and surface gravities between 4.0 and 5.5 dex. From our photometry and an M6 ± 1 spectral type for both components, we find luminosities of log(L/L⊙) = -2.11 ± 0.13 dex and log(L/L⊙) = -2.30 ± 0.16 dex for TWA22 A and B, respectively. By comparing these parameters with evolutionary models, we question the age and the multiplicity of this system. We also discuss a possible underestimation of the mass predicted by evolutionary models for young stars close to the substellar boundary. Based on service-mode observations (072.C-0644, 073.C-0469, 075.C-0521, 076.C-0554, 078.C-0510, 080.C-0581

Search for Wide Planetary-Mass Companions in Young Star-Forming Regions with UKIDSS and Pan-STARRS

NASA Astrophysics Data System (ADS)

Aller, Kimberly M.; Kraus, A. L.; Liu, M. C.; Bowler, B. P.

2013-01-01

Over the past decade, planetary-mass (<15 MJup) companions have been discovered in very wide orbits (>100 AU) around young stars. It is unclear whether these objects formed like planets or like stars. If these are planets, then modifications to core accretion or disk instability models are needed to allow formation at such wide orbits, or planet scattering must be an important mechanism. On the other hand, if these objects formed like stars, we need to understand the frequency of these extremely low mass ratio binary companions which challenge brown dwarf formation models. Regardless of their origins, these wide companions are easier to observe than close-in planets and can be used as benchmarks to understand the properties of young planets. We have combined optical and NIR photometry from UKIDSS and Pan-STARRS-1 to search the young star-forming region of Upper Scorpius and Taurus for new planetary-mass objects, going ≈3 mag deeper than previous work with 2MASS. We identified several candidates with very wide separations (≈400-4000 AU) from known members using a combination of color selection and spectral energy distribution (SED) fitting to templates of known low-mass stars and brown dwarfs. Furthermore, we have obtained followup NIR spectra of several Upper Scorpius candidates to spectroscopically identify three new wide very low-mass companions (≈15-25 MJup spectral type of M8-L0).

A survey for variable young stars with small telescopes: First results from HOYS-CAPS

NASA Astrophysics Data System (ADS)

Froebrich, D.; Campbell-White, J.; Scholz, A.; Eislöffel, J.; Zegmott, T.; Billington, S. J.; Donohoe, J.; Makin, S. V.; Hibbert, R.; Newport, R. J.; Pickard, R.; Quinn, N.; Rodda, T.; Piehler, G.; Shelley, M.; Parkinson, S.; Wiersema, K.; Walton, I.

2018-05-01

Variability in Young Stellar Objects (YSOs) is one of their primary characteristics. Long-term, multi-filter, high-cadence monitoring of large YSO samples is the key to understand the partly unusual light-curves that many of these objects show. Here we introduce and present the first results of the HOYS-CAPScitizen science project which aims to perform such monitoring for nearby (d < 1 kpc) and young (age < 10 Myr) clusters and star forming regions, visible from the northern hemisphere, with small telescopes. We have identified and characterised 466 variable (413 confirmed young) stars in 8 young, nearby clusters. All sources vary by at least 0.2 mag in V, have been observed at least 15 times in V, R and I in the same night over a period of about 2 yrs and have a Stetson index of larger than 1. This is one of the largest samples of variable YSOs observed over such a time-span and cadence in multiple filters. About two thirds of our sample are classical T-Tauri stars, while the rest are objects with depleted or transition disks. Objects characterised as bursters show by far the highest variability. Dippers and objects whose variability is dominated by occultations from normal interstellar dust or dust with larger grains (or opaque material) have smaller amplitudes. We have established a hierarchical clustering algorithm based on the light-curve properties which allows the identification of the YSOs with the most unusual behaviour, and to group sources with similar properties. We discuss in detail the light-curves of the unusual objects V2492 Cyg, V350 Cep and 2MASS J21383981+5708470.

DECam Survey for Substellar and Low-mass Stellar Members of Sco-Cen

NASA Astrophysics Data System (ADS)

Mamajek, Eric E.; Moolekamp, Fred; James, David; Luhman, Kevin; Pecaut, Mark; Metchev, Stanimir A.; Denbo, Sara; Bell, Cameron P. M.

2017-01-01

We present the results of a DECam imaging survey for low-mass stellar and substellar objects in the nearby Sco-Cen OB association. The DECam survey was taken in izY bands in 2013 and 2015 and covered $\\sim$87 deg$^2$ in the two nearest and oldest subgroups, Upper Cen-Lup ($\\sim$142 pc) and Lower Cen-Cru ($\\sim$118 pc; both with mean ages $\\sim$16 Myr). Using color-magnitude and proper motion selection, we identify 391 candidate Sco-Cen members with masses ranging from near the D-burning limit of $\\sim$13 M$_{Jup}$, through the H-burning limit, up to $\\sim$0.4 M$_\\odot$. Our initial spectroscopic follow-up with the ARCoIRIS and COSMOS spectrographs for 19 objects have yielded young M dwarfs showing signatures of low surface-gravity. Our survey yields the first constraints on the substellar and low-mass initial mass function and disk fraction in the two oldest Sco-Cen subgroups, and will yield a large sample of young, low-surface gravity M and L-type objects of constrained age, distance, and chemical composition. We acknowledge support from NSF award AST-1313029 and the REU Site in Physics and Astrophysics at the University of Rochester supported by NSF award PHY-1156339.

Dynamics of Variable Mass Systems

NASA Technical Reports Server (NTRS)

Eke, Fidelis O.

1998-01-01

This report presents the results of an investigation of the effects of mass loss on the attitude behavior of spinning bodies in flight. The principal goal is to determine whether there are circumstances under which the motion of variable mass systems can become unstable in the sense that their transverse angular velocities become unbounded. Obviously, results from a study of this kind would find immediate application in the aerospace field. The first part of this study features a complete and mathematically rigorous derivation of a set of equations that govern both the translational and rotational motions of general variable mass systems. The remainder of the study is then devoted to the application of the equations obtained to a systematic investigation of the effect of various mass loss scenarios on the dynamics of increasingly complex models of variable mass systems. It is found that mass loss can have a major impact on the dynamics of mechanical systems, including a possible change in the systems stability picture. Factors such as nozzle geometry, combustion chamber geometry, propellant's initial shape, size and relative mass, and propellant location can all have important influences on the system's dynamic behavior. The relative importance of these parameters on-system motion are quantified in a way that is useful for design purposes.

Association between low lean mass and low bone mineral density in 653 women with hip fracture: does the definition of low lean mass matter?

PubMed

Di Monaco, Marco; Castiglioni, Carlotta; Di Monaco, Roberto; Tappero, Rosa

2017-12-01

Loss of both muscle and bone mass results in fragility fractures with increased risk of disability, poor quality of life, and death. Our aim was to assess the association between low appendicular lean mass (aLM) defined according to different criteria and low bone mineral density (BMD) in hip-fracture women. Six hundred fifty-three women admitted to our rehabilitation hospital underwent dual energy X-ray absorptiometry 19.1 ± 4.1 (mean ± SD) days after hip-fracture occurrence. Low aLM was identified according to either Baumgartner's definition (aLM/height 2 less than two standard deviations below the mean of the young reference group) or FNIH criteria: aLM <15.02 kg, or aLM adjusted for body mass index (BMI) <0.512. Low BMD was diagnosed with a T-score <-2.5 at the unfractured femoral neck. Using Baumgartner's definition, the association between low aLM/height 2 and low BMD was significant: χ 2 (1, n = 653) = 8.52 (p = 0.004), but it was erased by adjustments for age and fat mass. Using the FNIH definition the association between low aLM and low BMD was significant: χ 2 (1, n = 653) = 42.5 (p < 0.001), and it was confirmed after adjustment for age and fat mass (p < 0.001). With the FNIH definition based on aLM/BMI ratio the association between low aLM/BMI ratio and low BMD was nonsignificant: χ 2 (1, n = 653) = 0.003 (p = 0.957). The association between low aLM and low BMD in women with hip fracture dramatically depends on the adopted definition of low aLM. FNIH threshold for aLM (<15.02 kg) emerges as a useful tool to capture women with damage of the muscle-bone unit.

THE FORMATION AND EVOLUTION OF YOUNG LOW-MASS STARS WITHIN HALOS WITH HIGH CONCENTRATION OF DARK MATTER PARTICLES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Casanellas, Jordi; Lopes, IlIDio, E-mail: jordicasanellas@ist.utl.p, E-mail: ilidio.lopes@ist.utl.p

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 {sub 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, thesemore » 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 (|DELTAT{sub eff}|>10{sup 3} 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{sub 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 rho{sub c}hi = 10{sup 9} GeV cm{sup -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.« less

Photometric search for variable stars in the young open cluster Berkeley 59

NASA Astrophysics Data System (ADS)

Lata, Sneh; Pandey, A. K.; Maheswar, G.; Mondal, Soumen; Kumar, Brijesh

2011-12-01

We present the time series photometry of stars located in the extremely young open cluster Berkeley 59. Using the 1.04-m telescope at Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, we have identified 42 variables in a field of ˜13 × 13 arcmin2 around the cluster. The probable members of the cluster have been identified using a (V, V-I) colour-magnitude diagram and a (J-H, H-K) colour-colour diagram. 31 variables have been found to be pre-main-sequence stars associated with the cluster. The ages and masses of the pre-main-sequence stars have been derived from the colour-magnitude diagram by fitting theoretical models to the observed data points. The ages of the majority of the probable pre-main-sequence variable candidates range from 1 to 5 Myr. The masses of these pre-main-sequence variable stars have been found to be in the range of ˜0.3 to ˜3.5 M⊙, and these could be T Tauri stars. The present statistics reveal that about 90 per cent T Tauri stars have period <15 d. The classical T Tauri stars are found to have a larger amplitude than the weak-line T Tauri stars. There is an indication that the amplitude decreases with an increase in mass, which could be due to the dispersal of the discs of relatively massive stars.

A Method to Estimate the Masses of Asymptotic Giant Branch Variable Stars

NASA Astrophysics Data System (ADS)

Takeuti, Mine; Nakagawa, Akiharu; Kurayama, Tomoharu; Honma, Mareki

2013-06-01

AGB variable stars are at the transient phase between low and high mass-loss rates; estimating the masses of these stars is necessary to study the evolutionary processes and mass-loss processes during the AGB stage. We applied the pulsation constant theoretically derived by Xiong and Deng (2007 MNRAS, 378, 1270) to 15 galactic AGB stars in order to estimate their masses. We found that using the pulsation constant is effective to estimate the mass of a star pulsating with two different pulsation modes, such as S Crt and RX Boo, which provides mass estimates comparable to theoretical results of AGB star evolution. We also extended the use of the pulsation constant to single-mode variables, and analyzed the properties of AGB stars related to their masses.

Pruning The ELM Survey: Characterizing Candidate Low-mass White Dwarfs through Photometric Variability

NASA Astrophysics Data System (ADS)

Bell, Keaton J.; Gianninas, A.; Hermes, J. J.; Winget, D. E.; Kilic, Mukremin; Montgomery, M. H.; Castanheira, B. G.; Vanderbosch, Z.; Winget, K. I.; Brown, Warren R.

2017-02-01

We assess the photometric variability of nine stars with spectroscopic Teff and log g values from the ELM Survey that locates them near the empirical extremely low-mass (ELM) white dwarf instability strip. We discover three new pulsating stars: SDSS J135512.34+195645.4, SDSS J173521.69+213440.6, and SDSS J213907.42+222708.9. However, these are among the few ELM Survey objects that do not show radial velocity (RV) variations that confirm the binary nature expected of helium-core white dwarfs. The dominant 4.31 hr pulsation in SDSS J135512.34+195645.4 far exceeds the theoretical cut-off for surface reflection in a white dwarf, and this target is likely a high-amplitude δ Scuti pulsator with an overestimated surface gravity. We estimate the probability to be less than 0.0008 that the lack of measured RV variations in four of eight other pulsating candidate ELM white dwarfs could be due to low orbital inclination. Two other targets exhibit variability as photometric binaries. Partial coverage of the 19.342 hr orbit of WD J030818.19+514011.5 reveals deep eclipses that imply a primary radius >0.4 R⊙—too large to be consistent with an ELM white dwarf. The only object for which our time series photometry adds support to ELM white dwarf classification is SDSS J105435.78-212155.9, which has consistent signatures of Doppler beaming and ellipsoidal variations. We conclude that the ELM Survey contains multiple false positives from another stellar population at Teff ≲ 9000 K, possibly related to the sdA stars recently reported from SDSS spectra.

An X-shooter survey of star forming regions: Low-mass stars and sub-stellar objects

NASA Astrophysics Data System (ADS)

Alcalá, J. M.; Stelzer, B.; Covino, E.; Cupani, G.; Natta, A.; Randich, S.; Rigliaco, E.; Spezzi, L.; Testi, L.; Bacciotti, F.; Bonito, R.; Covino, S.; Flaccomio, E.; Frasca, A.; Gandolfi, D.; Leone, F.; Micela, G.; Nisini, B.; Whelan, E.

2011-03-01

We present preliminary results of our X-shooter survey in star forming regions. In this contribution we focus on sub-samples of young stellar and sub-stellar objects (YSOs) in the Lupus star forming region and in the TW Hya association. We show that the X-shooter spectra are suitable for conducting several parallel studies such as YSO + disk fundamental parameters, accretion and outflow activity in the very low-mass (VLM) and sub-stellar regimes, as well as magnetic activity in young VLM YSOs, and Li abundance determinations. The capabilities of X-shooter in terms of wide spectral coverage, resolution and limiting magnitudes, allow us to assess simultaneously the accretion/outflow, magnetic activity, and disk diagnostics, from the UV and optical to the near-IR, avoiding ambiguities due to possible YSO variability. Based on observations collected at the European Southern Observatory, Chile, under Programmes 084.C-0269 and 085.C-0238.

The Low-Mass Stellar Initial Mass Function: Ultra-Faint Dwarf Galaxies Revisited

NASA Astrophysics Data System (ADS)

Platais, Imants

2017-08-01

The stellar Initial Mass Function plays a critical role in the evolution of the baryonic content of the Universe. The form of the low-mass IMF - stars of mass less than the solar mass - determines the fraction of baryons locked up for a Hubble time, and thus indicates how gas and metals are cycled through galaxies. Inferences from resolved stellar populations, where the low-mass luminosity function and associated IMF can be derived from direct star counts, generally favor an invariant and universal IMF. However, a recent study of ultra-faint dwarf galaxies Hercules and Leo IV indicates a bottom-lite IMF, over a narrow range of stellar mass (only 0.55-0.75 M_sun), correlated with the internal velocity dispersion and/or metallicity. We propose to obtain ultra-deep imaging for a significantly closer ultra-faint dwarf, Bootes I, which will allow us to construct the luminosity function down to M_v=+10 (equivalent to 0.35 solar mass). We will also re-analyze the HST archival observations for the Hercules and Leo IV dwarfs using the same updated techniques as for Bootes I. The combined datasets should provide a reliable answer to the question of how variable is the low-mass stellar IMF.

Identifying the Young Low-mass Stars within 25 pc. II. Distances, Kinematics, and Group Membership

NASA Astrophysics Data System (ADS)

Shkolnik, Evgenya L.; Anglada-Escudé, Guillem; Liu, Michael C.; Bowler, Brendan P.; Weinberger, Alycia J.; Boss, Alan P.; Reid, I. Neill; Tamura, Motohide

2012-10-01

We have conducted a kinematic study of 165 young M dwarfs with ages of lsim300 Myr. Our sample is composed of stars and brown dwarfs with spectral types ranging from K7 to L0, detected by ROSAT and with photometric distances of lsim25 pc assuming that the stars are single and on the main sequence. In order to find stars kinematically linked to known young moving groups (YMGs), we measured radial velocities for the complete sample with Keck and CFHT optical spectroscopy and trigonometric parallaxes for 75 of the M dwarfs with the CAPSCam instrument on the du Pont 2.5 m Telescope. Due to their youthful overluminosity and unresolved binarity, the original photometric distances for our sample underestimated the distances by 70% on average, excluding two extremely young (lsim3 Myr) objects found to have distances beyond a few hundred parsecs. We searched for kinematic matches to 14 reported YMGs and identified 10 new members of the AB Dor YMG and 2 of the Ursa Majoris group. Additional possible candidates include six Castor, four Ursa Majoris, two AB Dor members, and one member each of the Her-Lyr and β Pic groups. Our sample also contains 27 young low-mass stars and 4 brown dwarfs with ages lsim150 Myr that are not associated with any known YMG. We identified an additional 15 stars that are kinematic matches to one of the YMGs, but the ages from spectroscopic diagnostics and/or the positions on the sky do not match. These warn against grouping stars together based only on kinematics and that a confluence of evidence is required to claim that a group of stars originated from the same star-forming event. Based on observations collected at the W. M. Keck Observatory, the Canada-France-Hawaii Telescope, the du Pont Telescope at Las Campanas Observatory, and the Subaru Telescope. 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

Identifying the Young Low-mass Stars within 25 pc. I. Spectroscopic Observations

NASA Astrophysics Data System (ADS)

Shkolnik, Evgenya; Liu, Michael C.; Reid, I. Neill

2009-07-01

We have completed a high-resolution (R ≈ 60,000) optical spectroscopic survey of 185 nearby M dwarfs identified using ROSAT data to select active, young objects with fractional X-ray luminosities comparable to or greater than Pleiades members. Our targets are drawn from the NStars 20 pc census and the Moving-M sample with distances determined from parallaxes or spectrophotometric relations. We limited our sample to 25 pc from the Sun, prior to correcting for pre-main-sequence overluminosity or binarity. Nearly half of the resulting M dwarfs are not present in the Gliese catalog and have no previously published spectral types. We identified 30 spectroscopic binaries (SBs) from the sample, which have strong X-ray emission due to tidal spin-up rather than youth. This is equivalent to a 16% SB fraction, with at most a handful of undiscovered SBs. We estimate upper limits on the age of the remaining M dwarfs using spectroscopic youth indicators such as surface gravity-sensitive indices (CaH and K I). We find that for a sample of field stars with no metallicity measurements, a single CaH gravity index may not be sufficient, as higher metallicities mimic lower gravity. This is demonstrated in a subsample of metal-rich radial velocity (RV) standards, which appear to have low surface gravity as measured by the CaH index, yet show no other evidence of youth. We also use additional youth diagnostics such as lithium absorption and strong Hα emission to set more stringent age limits. Eleven M dwarfs with no Hα emission or absorption are likely old (>400 Myr) and were caught during an X-ray flare. We estimate that our final sample of the 144 youngest and nearest low-mass objects in the field is less than 300 Myr old, with 30% of them being younger than 150 Myr and four very young (lap10 Myr), representing a generally untapped and well-characterized resource of M dwarfs for intensive planet and disk searches. Based on observations collected at the W. M. Keck Observatory and

Perceived Discrimination and Mexican-Origin Young Adults' Sleep Duration and Variability: The Moderating Role of Cultural Orientations.

PubMed

Zeiders, Katharine H; Updegraff, Kimberly A; Kuo, Sally I-Chun; Umaña-Taylor, Adriana J; McHale, Susan M

2017-08-01

Perceived ethnic discrimination is central to the experiences of Latino young adults, yet we know little about the ways in which and the conditions under which ethnic discrimination relates to Latino young adults' sleep patterns. Using a sample of 246 Mexican-origin young adults (M age  = 21.11, SD = 1.54; 50 % female), the current study investigated the longitudinal links between perceived ethnic discrimination and both sleep duration and night-to-night variability in duration, while also examining the moderating roles of Anglo and Mexican orientations in the associations. The results revealed that perceived discrimination predicted greater sleep variability, and this link was not moderated by cultural orientations. The relation between perceived discrimination and hours of sleep, however, was moderated by Anglo and Mexican orientations. Individuals with high Anglo and Mexican orientations (bicultural) and those with only high Mexican orientations (enculturated), showed no association between discrimination and hours of sleep. Individuals with low Anglo and Mexican orientations (marginalized) displayed a positive association, whereas those with high Anglo and low Mexican orientations (acculturated) displayed a negative association. The results suggest that discrimination has long term effects on sleep variability of Mexican-origin young adults, regardless of cultural orientations; however, for sleep duration, bicultural and enculturated orientations are protective.

Pruning The ELM Survey: Characterizing Candidate Low-mass White Dwarfs through Photometric Variability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bell, Keaton J.; Winget, D. E.; Montgomery, M. H.

We assess the photometric variability of nine stars with spectroscopic T {sub eff} and log g values from the ELM Survey that locates them near the empirical extremely low-mass (ELM) white dwarf instability strip. We discover three new pulsating stars: SDSS J135512.34+195645.4, SDSS J173521.69+213440.6, and SDSS J213907.42+222708.9. However, these are among the few ELM Survey objects that do not show radial velocity (RV) variations that confirm the binary nature expected of helium-core white dwarfs. The dominant 4.31 hr pulsation in SDSS J135512.34+195645.4 far exceeds the theoretical cut-off for surface reflection in a white dwarf, and this target is likely amore » high-amplitude δ Scuti pulsator with an overestimated surface gravity. We estimate the probability to be less than 0.0008 that the lack of measured RV variations in four of eight other pulsating candidate ELM white dwarfs could be due to low orbital inclination. Two other targets exhibit variability as photometric binaries. Partial coverage of the 19.342 hr orbit of WD J030818.19+514011.5 reveals deep eclipses that imply a primary radius >0.4 R {sub ⊙}—too large to be consistent with an ELM white dwarf. The only object for which our time series photometry adds support to ELM white dwarf classification is SDSS J105435.78−212155.9, which has consistent signatures of Doppler beaming and ellipsoidal variations. We conclude that the ELM Survey contains multiple false positives from another stellar population at T {sub eff}≲9000 K, possibly related to the sdA stars recently reported from SDSS spectra.« less

CARMENES science preparation: characterisation of M dwarfs with low-resolution spectroscopy and search for low-mass wide companions to young stars

NASA Astrophysics Data System (ADS)

Alonso-Floriano, F. J.

2015-11-01

This thesis is focused on the study of low-mass objects that can be targets of exoplanet searches with near-infrared spectrographs in general and CARMENES (Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs; see Quirrenbach et al. 2014) in particular. The CARMENES consortium comprises 11 institutions from Germany and Spain that are building a high-resolution spectrograph (R=82,000) with two channels, visible (0.55 - 1.05 um) and infrared (0.95 - 1.7 um), for the 3.5 m Calar Alto telescope. It will observe a sample of 300 M dwarfs in 600 nights of guaranteed time during at least three years, starting in January 2016. The final sample will be chosen from the 2200 M dwarfs included in the CARMENCITA input catalogue. For these stars, we have obtained and collected a large amount of data: spectral types, radial and rotational velocities, photometry in several bands, etc. Part of the e effort of the science preparation necessary for the final selection of targets for CARMENES and other near-infrared spectrographs has been collected in two publications, which are presented in this PhD thesis. In the first publication (Alonso-Floriano et al., 2015A&A...577A.128A), we obtained low-resolution spectra for 753 stars using the CAFOS spectrograph at the 2.2 m Calar Alto telescope. The main goal was to derive accurate spectral types, which are fundamental parameters for the sample selection. We used a grid of 49 standard stars, from spectral types K3V to M8V, together with a double least-square minimisation technique and 31 spectral indices previously defined by other authors. In addition, we quantified the surface gravity, metallicity and chromospheric activity of the sample, in order to detect low-gravity stars (giants and very young), metal-poor and very metal-poor stars (subdwarfs), and very active stars. In the second publication (Alonso-Floriano et al., 2015A&A...583A..85A), we searched for common proper

Excess Vitamin Intake before Starvation does not Affect Body Mass, Organ Mass, or Blood Variables but Affects Urinary Excretion of Riboflavin in Starving Rats.

PubMed

Moriya, Aya; Fukuwatari, Tsutomu; Shibata, Katsumi

2013-01-01

B-vitamins are important for producing energy from amino acids, fatty acids, and glucose. The aim of this study was to elucidate the effects of excess vitamin intake before starvation on body mass, organ mass, blood, and biological variables as well as on urinary excretion of riboflavin in rats. Adult rats were fed two types of diets, one with a low vitamin content (minimum vitamin diet for optimum growth) and one with a sufficient amount of vitamins (excess vitamin diet). Body mass, organ mass, and blood variables were not affected by excess vitamin intake before starvation. Interestingly, urinary riboflavin excretion showed a different pattern. Urine riboflavin in the excess vitamin intake group declined gradually during starvation, whereas it increased in the low vitamin intake group. Excess vitamin intake before starvation does not affect body mass, organ mass, or blood variables but does affect the urinary excretion of riboflavin in starving rats.

Dietary patterns associated with fat and bone mass in young children123

PubMed Central

Khoury, Philip R; Claytor, Randal P; Copeland, Kristen A; Hornung, Richard W; Daniels, Stephen R; Kalkwarf, Heidi J

2010-01-01

Background: Obesity and osteoporosis have origins in childhood, and both are affected by dietary intake and physical activity. However, there is little information on what constitutes a diet that simultaneously promotes low fat mass and high bone mass accrual early in life. Objective: Our objective was to identify dietary patterns related to fat and bone mass in children during the age period of 3.8–7.8 y. Design: A total of 325 children contributed data from 13 visits over 4 separate study years (age ranges: 3.8–4.8, >4.8–5.8, >5.8–6.8, and >6.8–7.8 y). We performed reduced-rank regression to identify dietary patterns related to fat mass and bone mass measured by dual-energy X-ray absorptiometry for each study year. Covariables included race, sex, height, weight, energy intake, calcium intake, physical activity measured by accelerometry, and time spent viewing television and playing outdoors. Results: A dietary pattern characterized by a high intake of dark-green and deep-yellow vegetables was related to low fat mass and high bone mass; high processed-meat intake was related to high bone mass; and high fried-food intake was related to high fat mass. Dietary pattern scores remained related to fat mass and bone mass after all covariables were controlled for (P < 0.001–0.03). Conclusion: Beginning at preschool age, diets rich in dark-green and deep-yellow vegetables and low in fried foods may lead to healthy fat and bone mass accrual in young children. PMID:20519562

Young stars of low mass in the Gum nebula

NASA Technical Reports Server (NTRS)

Graham, J. A.; Heyer, Mark H.

1989-01-01

Observations are presented for four recently formed stars in the vicinity of the Gum nebula which are heavily obscured by surrounding dust and are associated with small reflection nebulae. HH46 is the only currently active star of the sample, and it is found to have a spectral type in the range of late G-early K, with superimposed emission lines of H-alpha, Ca II, Fe I, Fe II, and weak He I at near zero velocities. It is suggested that the observed scenario of low-mass stars in an older massive star environment may be analogous to the circumstances surrounding the birth of the sun.

Evolutionary sequences of very hot, low-mass, accreting white dwarfs with application to symbiotic variables and ultrasoft/supersoft low-luminosity x-ray sources

NASA Technical Reports Server (NTRS)

Sion, Edward M.; Starrfield, Sumner G.

1994-01-01

We present the first detailed model results of quasi-static evolutionary sequences of very hot low-mass white dwarfs accreting hydrogen-rich material at rates between 1 x 10(exp -7) and 1 x 10(exp -9) solar mass/yr. Most of the sequences were generated from starting models whose core thermal structures were not thermally relaxed in the thermal pulse cycle-averaged sense of an asymptotic giant branch stellar core. Hence, the evolution at constant accretion rate was not invariably characterized by series of identical shell flashes. Sequences exhibiting stable steady state nuclear burning at the accretion supply rate as well as sequences exhibiting recurrent thermonuclear shell flashes are presented and discussed. In some cases, the white dwarf accretors remain small (less than 10(exp 11) cm) and very hot even during the shell flash episode. They then experience continued but reduced hydrogen shell burning during the longer quiescent intervals while their surface temperatures increase both because of compressional heating and envelope structure readjustment in response to accretion over thousands of years. Both accretion and continued hydrogen burning power these models with luminosities of a few times 10(exp 37) ergs/s. We suggest that the physical properties of these model sequences are of considerable relevance to the observed outburst and quiescent behavior of those symbiotic variables and symbiotic novae containing low-mass white dwarfs. We also suggest that our models are relevant to the observational characteristics of the growing class of low-luminosity, supersoft/ultrasoft X-ray sources in globular clusters, and the Magellanic Clouds.

Accretion-induced variability links young stellar objects, white dwarfs, and black holes.

PubMed

Scaringi, Simone; Maccarone, Thomas J; Körding, Elmar; Knigge, Christian; Vaughan, Simon; Marsh, Thomas R; Aranzana, Ester; Dhillon, Vikram S; Barros, Susana C C

2015-10-01

The central engines of disc-accreting stellar-mass black holes appear to be scaled down versions of the supermassive black holes that power active galactic nuclei. However, if the physics of accretion is universal, it should also be possible to extend this scaling to other types of accreting systems, irrespective of accretor mass, size, or type. We examine new observations, obtained with Kepler/K2 and ULTRACAM, regarding accreting white dwarfs and young stellar objects. Every object in the sample displays the same linear correlation between the brightness of the source and its amplitude of variability (rms-flux relation) and obeys the same quantitative scaling relation as stellar-mass black holes and active galactic nuclei. We also show that the most important parameter in this scaling relation is the physical size of the accreting object. This establishes the universality of accretion physics from proto-stars still in the star-forming process to the supermassive black holes at the centers of galaxies.

Accretion-induced variability links young stellar objects, white dwarfs, and black holes

PubMed Central

Scaringi, Simone; Maccarone, Thomas J.; Körding, Elmar; Knigge, Christian; Vaughan, Simon; Marsh, Thomas R.; Aranzana, Ester; Dhillon, Vikram S.; Barros, Susana C. C.

2015-01-01

The central engines of disc-accreting stellar-mass black holes appear to be scaled down versions of the supermassive black holes that power active galactic nuclei. However, if the physics of accretion is universal, it should also be possible to extend this scaling to other types of accreting systems, irrespective of accretor mass, size, or type. We examine new observations, obtained with Kepler/K2 and ULTRACAM, regarding accreting white dwarfs and young stellar objects. Every object in the sample displays the same linear correlation between the brightness of the source and its amplitude of variability (rms-flux relation) and obeys the same quantitative scaling relation as stellar-mass black holes and active galactic nuclei. We also show that the most important parameter in this scaling relation is the physical size of the accreting object. This establishes the universality of accretion physics from proto-stars still in the star-forming process to the supermassive black holes at the centers of galaxies. PMID:26601307

Spectral Variability of Two Rapidly Rotating Brown Dwarfs: 2MASS J08354256-0819237 and 2MASS J18212815+1414010

NASA Astrophysics Data System (ADS)

Schlawin, E.; Burgasser, Adam J.; Karalidi, T.; Gizis, J. E.; Teske, J.

2017-11-01

L dwarfs exhibit low-level, rotationally modulated photometric variability generally associated with heterogeneous, cloud-covered atmospheres. The spectral character of these variations yields insight into the particle sizes and vertical structure of the clouds. Here, we present the results of a high-precision, ground-based, near-infrared, spectral monitoring study of two mid-type L dwarfs that have variability reported in the literature, 2MASS J08354256-0819237 and 2MASS J18212815+1414010, using the SpeX instrument on the Infrared Telescope Facility. By simultaneously observing a nearby reference star, we achieve < 0.15 % per-band sensitivity in relative brightness changes across the 0.9-2.4 μm bandwidth. We find that 2MASS J0835-0819 exhibits marginal (≲0.5% per band) variability with no clear spectral dependence, while 2MASS J1821+1414 varies by up to ±1.5% at 0.9 μm, with the variability amplitude declining toward longer wavelengths. The latter result extends the variability trend observed in prior HST/WFC3 spectral monitoring of 2MASS J1821+1414, and we show that the full 0.9-2.4 μm variability amplitude spectrum can be reproduced by Mie extinction from dust particles with a log-normal particle size distribution with a median radius of 0.24 μm. We do not detect statistically significant phase variations with wavelength. The different variability behavior of 2MASS J0835-0819 and 2MASS J1821+1414 suggests dependencies on viewing angle and/or overall cloud content, underlying factors that can be examined through a broader survey.

Welfare Reform and Labor Force Exit by Young, Low-Skilled Single Males.

PubMed

Groves, Lincoln H

2016-04-01

While the labor market woes of low-skilled male workers in the United States over the past several decades have been well documented, the academic literature identifying causal factors leading to declines in labor force participation (LFP) by young, low-skilled males remains scant. To address this gap, I use the timing and characteristics of welfare-reform policies implemented during the 1990s and fixed-effects, instrumental variable regression modeling to show that policies seeking to increase LFP rates for low-skilled single mothers inadvertently led to labor force exit by young, low-skilled single males. Using data from the Current Population Survey and a bundle of work inducements enacted by states throughout the 1990s as exogenous variation in a quasi-experimental design, I find that the roughly 10 percentage point increase in LFP for low-skilled single mothers facilitated by welfare reform resulted in a statistically significant 2.8 percentage point decline in LFP for young, low-skilled single males. After conducting a series of robustness checks, I conclude that this result is driven entirely by white males, who responded to welfare-reform policies with a 3.7 percentage point decline in labor supply. Young black males, as well as other groups of potentially affected workers, appear to be uninfluenced by the labor supply response of less-educated single mothers to welfare reform. Impacts on young, single white males are large and economically significant, suggesting that nearly 150,000 males departed the formal labor market in response to directed welfare-reform policies.

Combine body mass index and body fat percentage measures to improve the accuracy of obesity screening in young adults.

PubMed

Hung, Shang-Ping; Chen, Ching-Yu; Guo, Fei-Ran; Chang, Ching-I; Jan, Chyi-Feng

Obesity screening among young adult groups is meaningful. Body mass index (BMI) is limited to discriminate between fat and lean mass. Asian young adult group tends to have lower BMI and higher body fat percentage (BFP) than other ethnic groups. Accuracy of obesity screening by commonly used BMI criteria is unclear in young Taiwanese population. A total of 894 young adults (447 males and 447 females) aged 20-26 were recruited. BMI, regional fat percentage and BFP determined by bioelectrical impedance analysis (BIA) were measured. BMI cutoff points were based on the criteria adopted by the Ministry of Health and Welfare in Taiwan. Cutoff points of low or high BFP were defined as 24% in men and 31.4% in women. Prevalence of BFP defining obesity was 14.8% in young men and 27.3% in young women. 23.2% of young men and only 8.3% of young women were classified to overweight or obesity categories according to the BMI criteria. Disagreement was noticed mainly among overweight males and normal weight females. 68.7% of BMI defining overweight young men had low BFP; however, 29.7% of young women of BMI defining normal group had high BFP. Up to 69.7% of young women with high BFP would be missed by BMI category only. Disagreement between BMI and BFP was significant among young adults, especially young women. We suggest combining BMI and BIA for obesity and overweight screening in Asian young adults. Copyright © 2016 Asia Oceania Association for the Study of Obesity. Published by Elsevier Ltd. All rights reserved.

Young stars of low mass in the Gum nebula

DOE Office of Scientific and Technical Information (OSTI.GOV)

Graham, J.A.; Heyer, M.H.

1989-06-01

Observations are presented for four recently formed stars in the vicinity of the Gum nebula which are heavily obscured by surrounding dust and are associated with small reflection nebulae. HH46 is the only currently active star of the sample, and it is found to have a spectral type in the range of late G-early K, with superimposed emission lines of H-alpha, Ca II, Fe I, Fe II, and weak He I at near zero velocities. It is suggested that the observed scenario of low-mass stars in an older massive star environment may be analogous to the circumstances surrounding the birthmore » of the sun. 53 refs.« less

LOW-METALLICITY YOUNG CLUSTERS IN THE OUTER GALAXY. II. SH 2-208

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yasui, Chikako; Kobayashi, Naoto; Izumi, Natsuko

We obtained deep near-infrared images of Sh 2-208, one of the lowest-metallicity H ii regions in the Galaxy, [O/H] = −0.8 dex. We detected a young cluster in the center of the H ii region with a limiting magnitude of K = 18.0 mag (10 σ ), which corresponds to a mass detection limit of ∼0.2 M {sub ⊙}. This enables the comparison of star-forming properties under low metallicity with those of the solar neighborhood. We identified 89 cluster members. From the fitting of the K -band luminosity function (KLF), the age and distance of the cluster are estimated to be ∼0.5more » Myr and ∼4 kpc, respectively. The estimated young age is consistent with the detection of strong CO emission in the cluster region and the estimated large extinction of cluster members ( A{sub V}  ∼ 4–25 mag). The observed KLF suggests that the underlying initial mass function (IMF) of the low-metallicity cluster is not significantly different from canonical IMFs in the solar neighborhood in terms of both high-mass slope and IMF peak (characteristic mass). Despite the very young age, the disk fraction of the cluster is estimated at only 27% ± 6%, which is significantly lower than those in the solar metallicity. Those results are similar to Sh 2-207, which is another star-forming region close to Sh 2-208 with a separation of 12 pc, suggesting that their star-forming activities in low-metallicity environments are essentially identical to those in the solar neighborhood, except for the disk dispersal timescale. From large-scale mid-infrared images, we suggest that sequential star formation is taking place in Sh 2-207, Sh 2-208, and the surrounding region, triggered by an expanding bubble with a ∼30 pc radius.« less

Spectral and Structure Modeling of Low and High Mass Young Stars Using a Radiative Trasnfer Code

NASA Astrophysics Data System (ADS)

Robson Rocha, Will; Pilling, Sergio

The spectroscopy data from space telescopes (ISO, Spitzer, Herchel) shows that in addition to dust grains (e.g. silicates), there is also the presence of the frozen molecular species (astrophysical ices, such as H _{2}O, CO, CO _{2}, CH _{3}OH) in the circumstellar environments. In this work we present a study of the modeling of low and high mass young stellar objects (YSOs), where we highlight the importance in the use of the astrophysical ices processed by the radiation (UV, cosmic rays) comes from stars in formation process. This is important to characterize the physicochemical evolution of the ices distributed by the protostellar disk and its envelope in some situations. To perform this analysis, we gathered (i) observational data from Infrared Space Observatory (ISO) related with low mass protostar Elias29 and high mass protostar W33A, (ii) absorbance experimental data in the infrared spectral range used to determinate the optical constants of the materials observed around this objects and (iii) a powerful radiative transfer code to simulate the astrophysical environment (RADMC-3D, Dullemond et al, 2012). Briefly, the radiative transfer calculation of the YSOs was done employing the RADMC-3D code. The model outputs were the spectral energy distribution and theoretical images in different wavelengths of the studied objects. The functionality of this code is based on the Monte Carlo methodology in addition to Mie theory for interaction among radiation and matter. The observational data from different space telescopes was used as reference for comparison with the modeled data. The optical constants in the infrared, used as input in the models, were calculated directly from absorbance data obtained in the laboratory of both unprocessed and processed simulated interstellar samples by using NKABS code (Rocha & Pilling 2014). We show from this study that some absorption bands in the infrared, observed in the spectrum of Elias29 and W33A can arises after the ices

Low-Frequency Variability of the Yellow Sea Cold Water Mass Identified from the China Coastal Waters and Adjacent Seas Reanalysis

DTIC Science & Technology

2015-01-01

the bottom of the central trough has a shape that resembles a saddle. In July, the cold water that has a temperature lower than 10∘C covers a third of...the YSCWM The YSCWM is a large water mass covering a third of the bottom layer at its largest extension. It has relatively stable properties with low...in the wind stress and heat fluxes. In summer, ENSO has the strongest influence on the YSCWM variability. ENSO may exert influence on the third mode

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

Clinical Variability in Cardiovascular Disease Risk Factor Screening and Management in Adolescent and Young Adult Women with Polycystic Ovary Syndrome.

PubMed

Baer, Tamara E; Milliren, Carly E; Walls, Courtney; DiVasta, Amy D

2015-10-01

To review the clinical presentation, evaluation, and management of normal-weight (NW), overweight (OW), and obese (OB) adolescent and young adult women with polycystic ovary syndrome (PCOS) during a 2-year follow-up. Retrospective chart review. One hundred seventy-three adolescent and young adult women, aged 12-22 years, diagnosed with PCOS. Demographic, health data, and laboratory measures were abstracted from 3 clinic visits: baseline and 1- and 2-year follow-up. Subjects were classified as NW, OW, or OB. Longitudinal data were analyzed using repeated-measures analysis of variance. Body mass index, self-reported concerns, and lifestyle changes. Most patients (73%) were OW or OB. Family history of type 2 diabetes was greater in OW (38%) and OB (53%) patients compared with NW (22%) patients (P = .002). Acanthosis nigricans was identified in OW (62%) and OB (21%) patients but not in NW patients (0%; P < .001). OW and OB patients had higher fasting insulin (P < .001) and lower high-density lipoprotein cholesterol (P = .005) levels than NW patients, although screening rates were low. Body mass index Z-scores decreased in both OW and OB patients over time (0.07 unit/yr, P < .001). Most patients with PCOS were OW or OB. Substantial clinical variability existed in cardiovascular disease (CVD) screening; among those screened, OW and OB patients had greater CVD risk factors. Despite self-reported concerns about weight and diabetes risk among OW and OB patients, no clinically significant change in body mass index percentile occurred. Evidence-based interventions and recommendations for screening tests are needed to address CVD risk in adolescents and young adults with PCOS. Copyright © 2015 North American Society for Pediatric and Adolescent Gynecology. Published by Elsevier Inc. All rights reserved.

Food- and health-related correlates of self-reported body mass index among low-income mothers of young children

PubMed Central

McCurdy, Karen; Kisler, Tiffani; Gorman, Kathleen S.; Metallinos-Katsaras, Elizabeth

2015-01-01

Objective Examine how income-related challenges around food and health are associated with variation in self-reported maternal body weight among low-income mothers. Design Cross-sectional, correlational design. Convenience sample recruited from 7 daycare centers and a Supplemental Nutrition Assistance Program outreach project. Maternal self-report data collected between October 2009 and May 2011. Setting Two Northeastern cities. Participants Sample of 166 mothers; 67% overweight or obese, 55% Hispanic, 42% reporting household food insecurity (HFI). Main Outcome Measures Maternal self-reported height and weight to calculate Body Mass Index (BMI). Independent variables: food program participation, supermarket use, 8-item food shopping practices scale, HFI, maternal depressive symptoms, self-rated health (SRH). Analysis Hierarchical multiple regression analysis tested relationships between maternal BMI with the independent variables of interest, adjusting for demographic confounds. Results Shopping practices to stretch food dollars (P = .04), using community food assistance programs (P < .05), and HFI (P < .04) correlated with heavier maternal BMIs; higher SRH corresponded to lower BMIs (P =.004). Conclusions and Implications Some strategies low-income mothers use to manage food resources are associated with heavier BMIs. Nutrition educators, public health practitioners, and researchers need to collaboratively address the associations between these strategies, food insecurity, poor health, and unhealthy weight. PMID:25794991

Food- and health-related correlates of self-reported body mass index among low-income mothers of young children.

PubMed

McCurdy, Karen; Kisler, Tiffani; Gorman, Kathleen S; Metallinos-Katsaras, Elizabeth

2015-01-01

To examine how income-related challenges regarding food and health are associated with variation in self-reported maternal body weight among low-income mothers. Cross-sectional design. Two Northeastern cities. Seven day care centers and a Supplemental Nutrition Assistance Program outreach project. Sample of 166 mothers; 67% were overweight or obese, 55% were Hispanic, and 42% reported household food insecurity (HFI). Maternal self-reported height and weight to calculate body mass index (BMI). Independent variables were food program participation, supermarket use, 8-item food shopping practices scale, HFI, maternal depressive symptoms, and self-rated health. Hierarchical multiple regression analysis tested relationships between maternal BMI with the independent variables of interest, adjusting for demographic confounds. Shopping practices to stretch food dollars (P = .04), using community food assistance programs (P < .05), and HFI (P < .04) correlated with heavier maternal BMIs; higher self-rated health corresponded to lower BMIs (P = .004). Some strategies low-income mothers use to manage food resources are associated with heavier BMIs. Nutrition educators, public health practitioners, and researchers need to collaboratively address the associations between these strategies, food insecurity, poor health, and unhealthy weight. Copyright © 2015 Society for Nutrition Education and Behavior. Published by Elsevier Inc. All rights reserved.

The Origin of Variability of the Intermediate-mass Black-hole ULX System HLX-1 in ESO 243-49

NASA Astrophysics Data System (ADS)

Lasota, J.-P.; Alexander, T.; Dubus, G.; Barret, D.; Farrell, S. A.; Gehrels, N.; Godet, O.; Webb, N. A.

2011-07-01

The ultra-luminous (LX <~ 1042 erg s-1) intermediate-mass black-hole (IMBH) system HLX-1 in the ESO 243-49 galaxy exhibits variability with a possible recurrence time of a few hundred days. Finding the origin of this variability would constrain the still largely unknown properties of this extraordinary object. Since it exhibits a hardness-intensity behavior characteristic of black-hole X-ray transients, we have analyzed the variability of HLX-1 in the framework of the disk instability model that explains outbursts of such systems. We find that the long-term variability of HLX-1 is unlikely to be explained by a model in which outbursts are triggered by thermal-viscous instabilities in an accretion disk. Possible alternatives include the instability in a radiation-pressure-dominated disk but we argue that a more likely explanation is a modulated mass transfer due to tidal stripping of a star in an eccentric orbit around the IMBH. We consider an evolutionary scenario leading to the creation of such a system and estimate the probability of its observation. We conclude, using a simplified dynamical model of the post-collapse cluster, that no more than 1/100 to 1/10 of M • <~ 104 M sun IMBHs—formed by runaway stellar mergers in the dense collapsed cores of young clusters—could have a few ×1 M sun main-sequence star evolve to an asymptotic giant branch on an orbit eccentric enough for mass transfer at periapse, while avoiding collisional destruction or being scattered into the IMBH by two-body encounters. The finite but low probability of this configuration is consistent with the uniqueness of HLX-1. We note, however, that the actual response of a standard accretion disk to bursts of mass transfer may be too slow to explain the observations unless the orbit is close to parabolic (and hence even rarer). Also, increased heating, presumably linked to the highly time-dependent gravitational potential, could shorten the relevant timescales.

LkHα 262/263: the paradigm of multiplicity vs disk fraction in low-mass stellar systems.

NASA Astrophysics Data System (ADS)

Velasco, S.; Rebolo, R.; Oscoz, A.; Labadie, L.; Pérez-Garrido, A.

2017-03-01

The study of multiple systems and their link with the presence of discs around their components is key to understanding the evolution of low-mass pre-main sequence stars. Although there are indications that high-multiplicity systems are much more frequent among very young stars, until now, only a few of these young low-mass stellar systems have been confirmed. Here, we present high spatial resolution i band imaging of the system formed by LkHα 262 and LkHα 263, in the MBM12 cloud. It was obtained during the first commissioning period of the Adaptive Optics Lucky Imager (AOLI) at the 4.2 m William Herschel Telescope, using its Lucky Imaging mode. The multiple system LkHα 262/263 is composed of four low-mass very young M-type stars and some discs, including an edge-on disc around LkHα 263C. The AOLI data combined with previously available and newly obtained optical and infrared imaging show that the three components of LkHα 263 are co-moving, that there is orbital motion in the AB pair (0.41arcsec separation), and, remarkably, that LkHα 262-263 is a common proper motion system with a less than 1 mas/yr relative motion. According to BT-settl models the mass of each of the five components is close to 0.4 M and the age is in the range 1-2 Myr. We also give marginal evidence of a cooler companion to LkHα 262, at less than 0.15 arcsec, turning LkHα 262-263 into a five-component likely gravitationally bounded system. The presence of discs in some of the components offers an interesting opportunity to investigate the formation and evolution of discs in the early stages of multiple very low-mass systems.

Extreme Quiescent Variability of the Transient Neutron Star Low-mass X-ray Binary EXO 1745-248 in Terzan 5

NASA Astrophysics Data System (ADS)

Sandoval, L. E. Rivera; Wijnands, R.; Degenaar, N.; Cavecchi, Y.; Heinke, C. O.; Cackett, E. M.; Homan, J.; Altamirano, D.; Bahramian, A.; Sivakoff, G. R.; Miller, J. M.; Parikh, A. S.

2018-06-01

EXO 1745-248 is a transient neutron-star low-mass X-ray binary that resides in the globular cluster Terzan 5. We studied the transient during its quiescent state using 18 Chandra observations of the cluster acquired between 2003 and 2016. We found an extremely variable source, with a luminosity variation in the 0.5-10 keV energy range of ˜3 orders of magnitude (between 3 × 1031 erg s-1 and 2 × 1034 erg s-1) on time scales from years down to only a few days. Using an absorbed power-law model to fit its quiescent spectra, we obtained a typical photon index of ˜1.4, indicating that the source is even harder than during outburst and much harder than typical quiescent neutron stars if their quiescent X-ray spectra are also described by a single power-law model. This indicates that EXO 1745-248 is very hard throughout the entire observed X-ray luminosity range. At the highest luminosity, the spectrum fits better when an additional (soft) component is added to the model. All these quiescent properties are likely related to strong variability in the low-level accretion rate in the system. However, its extreme variable behavior is strikingly different from the one observed for other neutron star transients that are thought to still accrete in quiescence. We compare our results to these systems. We also discuss similarities and differences between our target and the transitional millisecond pulsar IGR J18245-2452, which also has hard spectra and strong variability during quiescence.

Type 2 diabetes is associated with low muscle mass in older adults.

PubMed

Kim, Kyung-Soo; Park, Kyung-Sun; Kim, Moon-Jong; Kim, Soo-Kyung; Cho, Yong-Wook; Park, Seok Won

2014-02-01

Our aim was to clarify the association between type 2 diabetes and the risk of low muscle mass in older adults. In the present study, 414 adults aged 65 years or older (144 patients with type 2 diabetes and 270 control participants) were included. Body composition was measured by dual-energy X-ray absorptiometry. Low muscle mass was defined as the appendicular skeletal muscle mass/height(2) (ASM/Ht(2)) or appendicular skeletal muscle mass/weight (ASM/Wt) of <2 SD below the sex-specific normal mean of the young reference group, or mass/weight (TSM/Wt) from control participants. Older men with type 2 diabetes showed significantly lower appendicular skeletal muscle mass than those without diabetes (19.5 ± 3.5 kg vs 21.0 ± 2.8 kg, P < 0.001). The prevalence of low muscle mass was consistently higher in older men with diabetes than those without diabetes defined by ASM/Ht(2) (57.6% vs 41.5%, P = 0.040), ASM/Wt (23.7% vs 12.3%, P = 0.046) and TSM/Wt (49.2% vs 20.0%, P < 0.001). In older women with diabetes, the prevalence of low muscle mass was higher than those without diabetes by ASM/Wt (25.9% vs 15.0%, P = 0.044) and TSM/Wt (32.9% vs 20.0%, P = 0.030), but not by ASM/Ht(2) (7.1% vs 8.6%, P = 0.685). The risk of low muscle mass was approximately two- to fourfold higher in older adults with type 2 diabetes, even after adjusting for age, body mass index, current smoking and other risk factors. In Korean older adults, type 2 diabetes is associated with low muscle mass. © 2014 Japan Geriatrics Society.

THE EXTREMELY RED, YOUNG L DWARF PSO J318.5338–22.8603: A FREE-FLOATING PLANETARY-MASS ANALOG TO DIRECTLY IMAGED YOUNG GAS-GIANT PLANETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Michael C.; Magnier, Eugene A.; Kotson, Michael C.

2013-11-10

We have discovered using Pan-STARRS1 an extremely red late-L dwarf, which has (J – K){sub MKO} = 2.78 and (J – K){sub 2MASS} = 2.84, making it the reddest known field dwarf and second only to 2MASS J1207–39b among substellar companions. Near-IR spectroscopy shows a spectral type of L7 ± 1 and reveals a triangular H-band continuum and weak alkali (K I and Na I) lines, hallmarks of low surface gravity. Near-IR astrometry from the Hawaii Infrared Parallax Program gives a distance of 24.6 ± 1.4 pc and indicates a much fainter J-band absolute magnitude than field L dwarfs. Themore » position and kinematics of PSO J318.5–22 point to membership in the β Pic moving group. Evolutionary models give a temperature of 1160{sup +30}{sub -40} K and a mass of 6.5{sup +1.3}{sub -1.0} M {sub Jup}, making PSO J318.5–22 one of the lowest mass free-floating objects in the solar neighborhood. This object adds to the growing list of low-gravity field L dwarfs and is the first to be strongly deficient in methane relative to its estimated temperature. Comparing their spectra suggests that young L dwarfs with similar ages and temperatures can have different spectral signatures of youth. For the two objects with well constrained ages (PSO J318.5–22 and 2MASS J0355+11), we find their temperatures are ≈400 K cooler than field objects of similar spectral type but their luminosities are similar, i.e., these young L dwarfs are very red and unusually cool but not 'underluminous'. Altogether, PSO J318.5–22 is the first free-floating object with the colors, magnitudes, spectrum, luminosity, and mass that overlap the young dusty planets around HR 8799 and 2MASS J1207–39.« less

Ambient temperature effect on pulse rate variability as an alternative to heart rate variability in young adult.

PubMed

Shin, Hangsik

2016-12-01

Pulse rate variability (PRV) is a promising physiological and analytic technique used as a substitute for heart rate variability (HRV). PRV is measured by pulse wave from various devices including mobile and wearable devices but HRV is only measured by an electrocardiogram (ECG). The purpose of this study was to evaluate PRV and HRV at various ambient temperatures and elaborate on the interchangeability of PRV and HRV. Twenty-eight healthy young subjects were enrolled in the experiment. We prepared temperature-controlled rooms and recorded the ECG and photoplethysmography (PPG) under temperature-controlled, constant humidity conditions. The rooms were kept at 17, 25, and 38 °C as low, moderate, and high ambient temperature environments, respectively. HRV and PRV were derived from the synchronized ECG and PPG measures and they were studied in time and frequency domain analysis for PRV/HRV ratio and pulse transit time (PTT). Similarity and differences between HRV and PRV were determined by a statistical analysis. PRV/HRV ratio analysis revealed that there was a significant difference between HRV and PRV for a given ambient temperature; this was with short-term variability measures such as SDNN SDSD or RMSSD, and HF-based variables including HF, LF/HF and normalized HF. In our analysis the absolute value of PTT was not significantly influenced by temperature. Standard deviation of PTT, however, showed significant difference not only between low and moderate temperatures but also between low and high temperatures. Our results suggest that ambient temperature induces a significant difference in PRV compared to HRV and that the difference becomes greater at a higher ambient temperature.

SPITZER OBSERVATIONS OF LONG-TERM INFRARED VARIABILITY AMONG YOUNG STELLAR OBJECTS IN CHAMAELEON I

DOE Office of Scientific and Technical Information (OSTI.GOV)

Flaherty, Kevin M.; Herbst, William; DeMarchi, Lindsay

Infrared variability is common among young stellar objects, with surveys finding daily to weekly fluctuations of a few tenths of a magnitude. Space-based observations can produce highly sampled infrared light curves, but are often limited to total baselines of about 1 month due to the orientation of the spacecraft. Here we present observations of the Chameleon I cluster, whose low declination makes it observable by the Spitzer Space Telescope over a 200-day period. We observe 30 young stellar objects with a daily cadence to better sample variability on timescales of months. We find that such variability is common, occurring inmore » ∼80% of the detected cluster members. The change in [3.6]–[4.5] color over 200 days for many of the sources falls between that expected for extinction and fluctuations in disk emission. With our high cadence and long baseline we can derive power spectral density curves covering two orders of magnitude in frequency and find significant power at low frequencies, up to the boundaries of our 200-day survey. Such long timescales are difficult to explain with variations driven by the interaction between the disk and stellar magnetic field, which has a dynamical timescale of days to weeks. The most likely explanation is either structural or temperature fluctuations spread throughout the inner ∼0.5 au of the disk, suggesting that the intrinsic dust structure is highly dynamic.« less

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.

Low-mass young stellar population and star formation history of the cluster IC 1805 in the W4 H II region

NASA Astrophysics Data System (ADS)

Panwar, Neelam; Samal, M. R.; Pandey, A. K.; Jose, J.; Chen, W. P.; Ojha, D. K.; Ogura, K.; Singh, H. P.; Yadav, R. K.

2017-07-01

W4 is a giant H II region ionized by the OB stars of the cluster IC 1805. The H II region/cluster complex has been a subject of numerous investigations as it is an excellent laboratory for studying the feedback effect of massive stars on the surrounding region. However, the low-mass stellar content of the cluster IC 1805 remains poorly studied till now. With the aim to unravel the low-mass stellar population of the cluster, we present the results of a multiwavelength study based on deep optical data obtained with the Canada-France-Hawaii Telescope, infrared data from Two Micron All Sky Survey and Spitzer Space Telescope and X-ray data from Chandra Space Telescope. The present optical data set is complete enough to detect stars down to 0.2 M⊙, which is the deepest optical observation so far for the cluster. We identified 384 candidate young stellar objects (YSOs; 101 Class I/II and 283 Class III) within the cluster using various colour-colour and colour-magnitude diagrams. We inferred the mean age of the identified YSOs to be ˜2.5 Myr and mass in the range 0.3-2.5 M⊙. The mass function of our YSO sample has a power-law index of -1.23 ± 0.23, close to the Salpeter value (-1.35), and consistent with those of other star-forming complexes. We explored the disc evolution of the cluster members and found that the disc-less sources are relatively older compared to the disc bearing YSO candidates. We examined the effect of high-mass stars on the circumstellar discs and within uncertainties, the influence of massive stars on the disc fraction seems to be insignificant. We also studied the spatial correlation of the YSOs with the distribution of gas and dust of the complex to conclude that IC 1805 would have formed in a large filamentary cloud.

THE GALACTIC CENTER CLOUD G2-A YOUNG LOW-MASS STAR WITH A STELLAR WIND

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scoville, N.; Burkert, A.

2013-05-10

We explore the possibility that the G2 gas cloud falling in toward SgrA* is the mass-loss envelope of a young T Tauri star. As the star plunges to smaller radius at 1000-6000 km s{sup -1}, a strong bow shock forms where the stellar wind is impacted by the hot X-ray emitting gas in the vicinity of SgrA*. For a stellar mass-loss rate of 4 Multiplication-Sign 10{sup -8} M{sub Sun} yr{sup -1} and wind velocity 100 km s{sup -1}, the bow shock will have an emission measure (EM = n {sup 2} vol) at a distance {approx}10{sup 16} cm, similar tomore » that inferred from the IR emission lines. The ionization of the dense bow shock gas is potentially provided by collisional ionization at the shock front and cooling radiation (X-ray and UV) from the post shock gas. The former would predict a constant line flux as a function of distance from SgrA*, while the latter will have increasing emission at lesser distances. In this model, the star and its mass-loss wind should survive pericenter passage since the wind is likely launched at 0.2 AU and this is much less than the Roche radius at pericenter ({approx}3 AU for a stellar mass of 2 M{sub Sun }). In this model, the emission cloud will probably survive pericenter passage, discriminating this scenario from others.« less

PSYM-WIDE: A Survey for Large-separation Planetary-mass Companions to Late Spectral Type Members of Young Moving Groups

NASA Astrophysics Data System (ADS)

Naud, Marie-Eve; Artigau, Étienne; Doyon, René; Malo, Lison; Gagné, Jonathan; Lafrenière, David; Wolf, Christian; Magnier, Eugene A.

2017-09-01

We present the results of a direct imaging survey for very large separation (>100 au), low-mass companions around 95 nearby young K5-L5 stars and brown dwarfs. They are high-likelihood candidates or confirmed members of the young (≲150 Myr) β Pictoris and AB Doradus moving groups (ABDMG) and the TW Hya, Tucana-Horologium, Columba, Carina, and Argus associations. Images in I\\prime and z\\prime filters were obtained with the Gemini Multi-Object Spectrograph (GMOS) on Gemini South to search for companions down to an apparent magnitude of z\\prime ˜ 22-24 at separations ≳20″ from the targets and in the remainder of the wide 5.‧5 × 5.‧5 GMOS field of view. This allowed us to probe the most distant region where planetary-mass companions could be gravitationally bound to the targets. This region was left largely unstudied by past high-contrast imaging surveys, which probed much closer-in separations. This survey led to the discovery of a planetary-mass (9-13 {M}{Jup}) companion at 2000 au from the M3V star GU Psc, a highly probable member of ABDMG. No other substellar companions were identified. These results allowed us to constrain the frequency of distant planetary-mass companions (5-13 {M}{Jup}) to {0.84}-0.66+6.73% (95% confidence) at semimajor axes between 500 and 5000 au around young K5-L5 stars and brown dwarfs. This is consistent with other studies suggesting that gravitationally bound planetary-mass companions at wide separations from low-mass stars are relatively rare.

Voluntary sway and rapid orthogonal transitions of voluntary sway in young adults, and low and high fall-risk older adults.

PubMed

Tucker, Murray G; Kavanagh, Justin J; Morrison, Steven; Barrett, Rod S

2009-10-01

Falls amongst older people have been linked to reduced postural stability and slowed movement responses. The objective of this study was to examine differences in postural stability and the speed of response between young adults, low fall-risk older adults, and high fall-risk older adults during voluntary postural sway movements. Twenty-five young adults (25+/-4 years), and 32 low fall-risk (74+/-5 years), and 16 high fall-risk (79+/-7 years) older adults performed voluntary sway and rapid orthogonal transitions of voluntary sway between the anterior-posterior and medial-lateral directions. Measures included reaction and movement time and the amplitudes of the centre of pressure, centre of mass, and the separation distance between the centre of pressure and centre of mass. Both fall-risk groups compared to the young had slower reaction and movement time, greater centre of pressure and/or centre of mass amplitude in the orthogonal (non-target) direction during voluntary sway, and reduced anterior-posterior and medial-lateral separation between the centre of pressure and centre of mass during voluntary sway and orthogonal transitions. High compared to low fall-risk individuals had slower reaction and movement time, increased non-target centre of mass amplitude during voluntary sway, and reduced medial-lateral centre of pressure and centre of mass separation during voluntary sway and orthogonal transitions. Age-related deterioration of postural control resulted in slower reactive responses and reduced control of the direction of body movement during voluntary sway and orthogonal transitions. Slower postural reaction and movement time and reduced medial-lateral control of the centre of mass during voluntary sway movements are associated with increased fall-risk in community-living older people.

Longitudinal multiple imputation approaches for body mass index or other variables with very low individual-level variability: the mibmi command in Stata.

PubMed

Kontopantelis, Evangelos; Parisi, Rosa; Springate, David A; Reeves, David

2017-01-13

In modern health care systems, the computerization of all aspects of clinical care has led to the development of large data repositories. For example, in the UK, large primary care databases hold millions of electronic medical records, with detailed information on diagnoses, treatments, outcomes and consultations. Careful analyses of these observational datasets of routinely collected data can complement evidence from clinical trials or even answer research questions that cannot been addressed in an experimental setting. However, 'missingness' is a common problem for routinely collected data, especially for biological parameters over time. Absence of complete data for the whole of a individual's study period is a potential bias risk and standard complete-case approaches may lead to biased estimates. However, the structure of the data values makes standard cross-sectional multiple-imputation approaches unsuitable. In this paper we propose and evaluate mibmi, a new command for cleaning and imputing longitudinal body mass index data. The regression-based data cleaning aspects of the algorithm can be useful when researchers analyze messy longitudinal data. Although the multiple imputation algorithm is computationally expensive, it performed similarly or even better to existing alternatives, when interpolating observations. The mibmi algorithm can be a useful tool for analyzing longitudinal body mass index data, or other longitudinal data with very low individual-level variability.

Variability of the lowest mass objects in the AB Doradus moving group

NASA Astrophysics Data System (ADS)

Vos, Johanna M.; Allers, Katelyn N.; Biller, Beth A.; Liu, Michael C.; Dupuy, Trent J.; Gallimore, Jack F.; Adenuga, Iyadunni J.; Best, William M. J.

2018-02-01

We present the detection of [3.6 μm] photometric variability in two young, L/T transition brown dwarfs, WISE J004701.06+680352.1 (W0047) and 2MASS J2244316+204343 (2M2244) using the Spitzer Space Telescope. We find a period of 16.4 ± 0.2 h and a peak-to-peak amplitude of 1.07 ± 0.04 per cent for W0047, and a period of 11 ± 2 h and amplitude of 0.8 ± 0.2 per cent for 2M2244. This period is significantly longer than that measured previously during a shorter observation. We additionally detect significant J-band variability in 2M2244 using the Wide-Field Camera on UKIRT. We determine the radial and rotational velocities of both objects using Keck NIRSPEC data. We find a radial velocity of -16.0_{-0.9}^{+0.8} km s-1 for 2M2244, and confirm it as a bona fide member of the AB Doradus moving group. We find rotational velocities of v sin i = 9.8 ± 0.3 and 14.3^{+1.4}_{-1.5} km s-1 for W0047 and 2M2244, respectively. With inclination angles of 85°+5-9 and 76°+14-20, W0047 and 2M2244 are viewed roughly equator-on. Their remarkably similar colours, spectra and inclinations are consistent with the possibility that viewing angle may influence atmospheric appearance. We additionally present Spitzer [4.5 μm] monitoring of the young, T5.5 object SDSS111010+011613 (SDSS1110) where we detect no variability. For periods <18 h, we place an upper limit of 1.25 per cent on the peak-to-peak variability amplitude of SDSS1110.

Body mass index and health-related quality of life among young Swiss men.

PubMed

Dey, Michelle; Gmel, Gerhard; Mohler-Kuo, Meichun

2013-10-30

Studies about the association between body mass index (BMI) and health-related quality of life (HRQOL) are often limited, because they 1) did not include a broad range of health-risk behaviors as covariates; 2) relied on clinical samples, which might lead to biased results; and 3) did not incorporate underweight individuals. Hence, this study aims to examine associations between BMI (from being underweight through obesity) and HRQOL in a population-based sample, while considering multiple health-risk behaviors (low physical activity, risky alcohol consumption, daily cigarette smoking, frequent cannabis use) as well as socio-demographic characteristics. A total of 5 387 young Swiss men (mean age = 19.99; standard deviation = 1.24) of a cross-sectional population-based study were included. BMI was calculated (kg/m²) based on self-reported height and weight and divided into 'underweight' (<18.5), 'normal weight' (18.5-24.9), 'overweight' (25.0-29.9) and 'obese' (≥30.0). Mental and physical HRQOL was assessed via the SF-12v2. Self-reported information on physical activity, substance use (alcohol, cigarettes, and cannabis) and socio-demographic characteristics also was collected. Logistic regression analyses were conducted to study the associations between BMI categories and below average mental or physical HRQOL. Substance use variables and socio-demographic variables were used as covariates. Altogether, 76.3% were normal weight, whereas 3.3% were underweight, 16.5% overweight and 3.9% obese. Being overweight or obese was associated with reduced physical HRQOL (adjusted OR [95% CI] = 1.58 [1.18-2.13] and 2.45 [1.57-3.83], respectively), whereas being underweight predicted reduced mental HRQOL (adjusted OR [95% CI] = 1.49 [1.08-2.05]). Surprisingly, obesity decreased the likelihood of experiencing below average mental HRQOL (adjusted OR [95% CI] = 0.66 [0.46-0.94]). Besides BMI, expressed as a categorical variable, all health-risk behaviors and socio

Variable interstellar absorption lines in young stellar aggregates

NASA Astrophysics Data System (ADS)

Krełowski, J.; Strobel, A.; Vješnica, S.; Melekh, D.; Bondar, A.

2018-06-01

The variability of interstellar atomic lines, sporadically reported in the astronomical literature, has been confirmed both in the case of the nearby hot star δ Ori and the very young and violent star-forming region η Carinae, using high-resolution echelle spectra. The presented variability concerns the intensities and profiles of Na I, K I and Ca II. The time-scale of the above-mentioned variations clearly suggests very local phenomena as their cause. It is important to say that not all interstellar lines vary in unison.

Investigating young children's learning of mass measurement

NASA Astrophysics Data System (ADS)

Cheeseman, Jill; McDonough, Andrea; Ferguson, Sarah

2014-06-01

This paper reports results of a design experiment regarding young children's concepts of mass measurement. The research built on an earlier study in which a framework of "growth points" in early mathematics learning and a related, task-based, one-to-one interview to assess children's understanding of the measurement of mass were developed. Prompted by the results and recommendations from the earlier study, five lessons were developed that offered rich learning experiences regarding concepts of mass. The 119 Year 1 and 2 children participating in the study were interviewed using the same protocol before and after the teaching period. The assessment data showed that the majority of these children moved from using nonstandard units to using standard units and instruments for measuring mass. The findings from this study challenge the traditional approach of using informal units for an extended period before the introduction of standard units.

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.

JVLA Observations of Young Brown Dwarfs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodríguez, Luis F.; Zapata, Luis A.; Palau, Aina, E-mail: l.rodriguez@crya.unam.mx, E-mail: l.zapata@crya.unam.mx, E-mail: a.palau@crya.unam.mx

We present sensitive 3.0 cm JVLA radio continuum observations of six regions of low-mass star formation that include twelve young brown dwarfs (BDs) and four young BD candidates. We detect a total of 49 compact radio sources in the fields observed, of which 24 have no reported counterparts and are considered new detections. Twelve of the radio sources show variability in timescales of weeks to months, suggesting gyrosynchrotron emission produced in active magnetospheres. Only one of the target BDs, FU Tau A, was detected. However, we detected radio emission associated with two of the BD candidates, WL 20S and CHLTmore » 2. The radio flux densities of the sources associated with these BD candidates are more than an order of magnitude larger than expected for a BD and suggest a revision of their classification. In contrast, FU Tau A falls on the well-known correlation between radio luminosity and bolometric luminosity, suggesting that the emission comes from a thermal jet and that this BD seems to be forming as a scaled-down version of low-mass stars.« less

Tuning Into Brown Dwarfs: Long-Term Radio Monitoring of Two Very Low Mass Dwarfs

NASA Astrophysics Data System (ADS)

Van Linge, Russell; Burgasser, Adam J.; Melis, Carl; Williams, Peter K. G.

2017-01-01

The very lowest-mass (VLM) stars and brown dwarfs, with effective temperatures T < 3000 K, exhibit mixed magnetic activity trends, with H-alpha and X-ray emission that declines rapidly beyond type M7/M8, but persistent radio emission in roughly 10-20% of sources. The dozen or so VLM radio emitters known show a broad range of emission characteristics and time-dependent behavior, including steady persistent emission, periodic oscillations, periodic polarized bursts, and aperiodic flares. Understanding the evolution of these variability patterns, and in particular whether they undergo solar-like cycles, requires long-term monitoring. We report the results of a long-term JVLA monitoring program of two magnetically-active VLM dwarf binaries, the young M7 2MASS 1314+1320AB and older L5 2MASS 1315-2649AB. On the bi-weekly cadence, 2MASS 1314 continues to show variability by revealing regular flaring while 2MASS 1315 continues to be a quiescent emitter. On the daily time scale, both sources show a mean flux density that can vary significantly just over a few days. These results suggest long-term radio behavior in radio-emitting VLM dwarfs is just as diverse and complex as short-term behavior.

FUNDAMENTAL PARAMETERS AND SPECTRAL ENERGY DISTRIBUTIONS OF YOUNG AND FIELD AGE OBJECTS WITH MASSES SPANNING THE STELLAR TO PLANETARY REGIME

DOE Office of Scientific and Technical Information (OSTI.GOV)

Filippazzo, Joseph C.; Rice, Emily L.; Faherty, Jacqueline

We combine optical, near-infrared, and mid-infrared spectra and photometry to construct expanded spectral energy distributions for 145 field age (>500 Myr) and 53 young (lower age estimate <500 Myr) ultracool dwarfs (M6-T9). This range of spectral types includes very low mass stars, brown dwarfs, and planetary mass objects, providing fundamental parameters across both the hydrogen and deuterium burning minimum masses for the largest sample assembled to date. A subsample of 29 objects have well constrained ages as probable members of a nearby young moving group. We use 182 parallaxes and 16 kinematic distances to determine precise bolometric luminosities (L{sub bol})more » and radius estimates from evolutionary models give semi-empirical effective temperatures (T{sub eff}) for the full range of young and field age late-M, L, and T dwarfs. We construct age-sensitive relationships of luminosity, temperature, and absolute magnitude as functions of spectral type and absolute magnitude to disentangle the effects of degenerate physical parameters such as T{sub eff}, surface gravity, and clouds on spectral morphology. We report bolometric corrections in J for both field age and young objects and find differences of up to a magnitude for late-L dwarfs. Our correction in Ks shows a larger dispersion but not necessarily a different relationship for young and field age sequences. We also characterize the NIR–MIR reddening of low gravity L dwarfs and identify a systematically cooler T{sub eff} of up to 300 K from field age objects of the same spectral type and 400 K cooler from field age objects of the same M{sub H} magnitude.« less

Factors associated with six-year weight change in young and middle-aged adults in the Young Finns Study.

PubMed

Kaikkonen, Jari E; Mikkilä, Vera; Juonala, Markus; Keltikangas-Järvinen, Liisa; Hintsanen, Mirka; Pulkki-Råback, Laura; Viikari, Jorma S A; Kähönen, Mika; Lehtimäki, Terho; Telama, Risto; Raitakari, Olli T

2015-04-01

To examine factors associated with weight change and obesity risk in young and middle-aged adults. The Young Finns Study with its 923 women and 792 men aged 24-39 years at baseline were followed for six years. Variables associated with the weight change were investigated with regression models. The average weight change was 0.45 kg/year in women and 0.58 kg/year in men. In women, weight change was steady across all ages. In men, weight changes were more pronounced in younger age groups. In women (weight gain > 2 kg, n = 490), medication for anxiety, low occupational status, high baseline BMI (body mass index), high intake of sweet beverages, high childhood BMI, high salt (NaCl and/or KCl) use, low number of children, low childhood family income, high stature and low level of dependence (a temperament subscale) were associated with increased weight gain (in the order of importance). In men (weight gain > 2 kg, n = 455), high stature, high intake of french fries, low intake of sweet cookies, young age, recent divorce, low intake of cereals, high intake of milk, depressive symptoms, rural childhood origin, high baseline BMI and unemployment were associated with more pronounced weight gain. Sedentarity (screen-time) was associated with weight gain only in young men. Physical activity and genetic risk for high BMI (score of 31 known variants) were not consistently associated with weight change. Socio-economic factors, temperamental and physical characteristics, and some dietary factors are related with weight change in young/middle-aged adults. The weight change occurring in adulthood is also determined by childhood factors, such as high BMI and low family income.

High respiratory quotient is associated with increases in body weight and fat mass in young adults.

PubMed

Shook, R P; Hand, G A; Paluch, A E; Wang, X; Moran, R; Hébert, J R; Jakicic, J M; Blair, S N

2016-10-01

Metabolic disturbances, such as reduced rates of fat oxidation (high respiratory quotient (RQ)) or low energy expenditure (low resting metabolic rate (RMR)), may contribute to obesity. The objective was to determine the association between a high RQ or a low RMR and changes in body weight and body composition over 1 year. We measured RQ and RMR in 341 adults using indirect calorimetry, along with body weight/body composition using dual-energy X-ray absorptiometery, energy expenditure using an arm-based activity monitor and energy intake using dietary recalls. Participants were classified into low, moderate or high RQ and RMR (adjusted for age, sex, race and body composition) groups according to tertiles by sex. Follow-up measurements were completed every 3 months. Individuals with a high RQ had larger gains in body weight and fat mass compared with individuals with a low/moderate RQ at month 3, and increases in fat mass were more than double among individuals with a high RQ at 12 months (1.3±3.0 vs 0.6±3.7 kg, P=0.03). Individuals with a low RMR did not gain more body weight nor fat mass compared with individuals with a moderate/high RMR. The primary finding is a high RQ is predictive of gains in body weight and fat mass over a 12-month period among young adults, with changes occurring as soon as 3 months. In addition, a low RMR was not associated with gains in body weight or fat mass over the same period.

An unusual very low-mass high-amplitude pre-main sequence periodic variable

NASA Astrophysics Data System (ADS)

Rodríguez-Ledesma, M. V.; Mundt, R.; Ibrahimov, M.; Messina, S.; Parihar, P.; Hessman, F. V.; Alves de Oliveira, C.; Herbst, W.

2012-08-01

Aims: We have investigated the nature of the variability of CHS 7797, an unusual periodic variable in the Orion Nebula Cluster. Methods: An extensive I-band photometric data set of CHS 7797 was compiled between 2004-2010 using various telescopes. Further optical data have been collected in R and z' bands. In addition, simultaneous observations of the ONC region including CHS 7797 were performed in the I,J,Ks & IRAC 3.6 and 4.5 μm bands over a time interval of ≈40 d. Results: CHS 7797 shows an unusual large-amplitude variation of ≈1.7 mag in the R,I, and z' bands with a period 17.786 ± 0.03 d (FAP = 1 × 10-15%). The amplitude of the brightness modulation decreases only slightly at longer wavelengths. The star is faint during ≈2/3 of the period and the shape of the phased light-curves for the seven different observing seasons shows minor changes and small-amplitude variations. Interestingly, there are no significant colour-flux correlations for λ ≲ 2 μm, while the object becomes redder when fainter at longer wavelengths. CHS 7797 has a spectral type of M 6 and an estimated mass between 0.04-0.1 M⊙. Conclusions: The analysis of the data suggests that the periodic variability of CHS 7797 is most probably caused by an orbital motion. Variability as a result of rotational brightness modulation by a hot spot is excluded by the lack of any colour-brightness correlation in the optical. The latter indicates that CHS 7797 is most probably occulted by circumstellar matter in which grains have grown from typical 0.1 μm to ≈1-2 μm sizes. We discuss two possible scenarios in which CHS 7797 is periodically eclipsed by structures in a disc, namely that CHS 7797 is a single object with a circumstellar disc, or that CHS 7797 is a binary system, similar to KH 15D, in which an inclined circumbinary disc is responsible of the variability. Possible reasons for the typical 0.3 mag variations in I-band at a given phase are discussed.

Rotational velocities of newly discovered, low-mass members of the Alpha Persei cluster

NASA Technical Reports Server (NTRS)

Stauffer, John R.; Hartmann, Lee W.; Jones, Burton F.

1989-01-01

About 30 new, low-mass members of the young open cluster Alpha Persei are identified via a proper-motion study and subsequent photometric and spectroscopic observations. Membership in the cluster is confirmed for a number of the fainter proper-motion candidates from Heckman, Dieckvoss, and Kox (1956). Coordinates, finding charts, BVRI photometry, and rotational velocities are provided for most of the stars. At least two of the stars show peculiar H-alpha emission profiles, with weak but very broad emission wings, and relatively narrow absorption reversals. The rotational velocity distribution for low-mass stars in the Alpha Per cluster are compared with recently derived rotational velocity distributions for T Tauri stars, placing strong constraints on the mechanisms for angular momentum loss during pre-main-sequence evolution.

Mass media interventions for preventing smoking in young people.

PubMed

Carson, Kristin V; Ameer, Faisal; Sayehmiri, Kourosh; Hnin, Khin; van Agteren, Joseph Em; Sayehmiri, Fatemeh; Brinn, Malcolm P; Esterman, Adrian J; Chang, Anne B; Smith, Brian J

2017-06-02

campaigns, one of which is new for this update. Seven of the studies used a controlled trial design and one an interrupted time-series analysis. Risks of bias were high across all included studies and there was considerable heterogeneity in study design, intervention and population being assessed.Three studies (n = 17,385), one of which compared a mass media intervention to no intervention and two of which evaluated mass media interventions as adjuncts to school-based interventions, found that the mass media interventions reduced the smoking behaviour of young people. The remaining five studies (n = 72,740) did not detect a significant effect on smoking behaviour. These included three studies comparing a mass media intervention to no intervention, one study evaluating a mass media intervention as an adjunct to a school-based intervention, and one interrupted time-series study of a social media intervention. The three campaigns which found a significant effect described their theoretical basis, used formative research in designing the campaign messages, and used message broadcast of reasonable intensity over extensive periods of time. However, some of the campaigns which did not detect an effect also exhibited these characteristics. Effective campaigns tended to last longer (minimum 3 years) and were more intense (more contact time) for both school-based lessons (minimum eight lessons per grade) and media spots (minimum four weeks' duration across multiple media channels with between 167 and 350 TV and radio spots). Implementation of combined school-based components (e.g. school posters) and the use of repetitive media messages delivered by multiple channels (e.g. newspapers, radio, television) appeared to contribute to successful campaigns. Certainty about the effects of mass media campaigns on smoking behaviour in youth is very low, due to inconsistency between studies in both design and results, and due to methodological issues amongst the included studies. It would

A deep staring campaign in the σ Orionis cluster. Variability in substellar members

NASA Astrophysics Data System (ADS)

Elliott, P.; Scholz, A.; Jayawardhana, R.; Eislöffel, J.; Hébrard, E. M.

2017-12-01

Context. The young star cluster near σ Orionis is one of the primary environments to study the properties of young brown dwarfs down to masses comparable to those of giant planets. Aims: Deep optical imaging is used to study time-domain properties of young brown dwarfs over typical rotational timescales and to search for new substellar and planetary-mass cluster members. Methods: We used the Visible Multi Object Spectrograph (VIMOS) at the Very Large Telescope (VLT) to monitor a 24'× 16' field in the I-band. We stared at the same area over a total integration time of 21 h, spanning three observing nights. Using the individual images from this run we investigated the photometric time series of nine substellar cluster members with masses from 10 to 60 MJup. The deep stacked image shows cluster members down to ≈5 MJup. We searched for new planetary-mass objects by combining our deep I-band photometry with public J-band magnitudes and by examining the nearby environment of known very low mass members for possible companions. Results: We find two brown dwarfs, with significantly variable, aperiodic light curves, both with masses around 50 MJup, one of which was previously unknown to be variable. The physical mechanism responsible for the observed variability is likely to be different for the two objects. The variability of the first object, a single-lined spectroscopic binary, is most likely linked to its accretion disc; the second may be caused by variable extinction by large grains. We find five new candidate members from the colour-magnitude diagram and three from a search for companions within 2000 au. We rule all eight sources out as potential members based on non-stellar shape and/or infrared colours. The I-band photometry is made available as a public dataset. Conclusions: We present two variable brown dwarfs. One is consistent with ongoing accretion, the other exhibits apparent transient variability without the presence of an accretion disc. Our analysis

Search for Low-mass Objects in the Globular Cluster M4. I. Detection of Variable Stars

NASA Astrophysics Data System (ADS)

Safonova, M.; Mkrtichian, D.; Hasan, P.; Sutaria, F.; Brosch, N.; Gorbikov, E.; Joseph, P.

2016-02-01

With every new discovery of an extrasolar planet, the absence of planets in globular clusters (GCs) becomes more and more conspicuous. Null detection of transiting hot Jupiters in GCs 47 Tuc, ω Cen, and NGC 6397 presents an important puzzle, raising questions about the role played by cluster metallicity and environment on formation and survival of planetary systems in densely populated stellar clusters. GCs were postulated to have many free-floating planets, for which microlensing (ML) is an established tool for detection. Dense environments, well-constrained distances and kinematics of lenses and sources, and photometry of thousands of stars simultaneously make GCs the ideal targets to search for ML. We present first results of a multisite, 69-night-long campaign to search for ML signatures of low-mass objects in the GC M4, which was chosen because of its proximity, location, and the actual existence of a planet. M4 was observed in R and I bands by two telescopes, 1 m T40 and 18-inch C18, of the Wise Observatory, Tel Aviv, Israel, from 2011 April to July. Observations on the 1 m telescope were carried out in service mode, gathering 12 to 48 20 s exposures per night for a total of 69 nights. C18 observations were done for about 4 hr a night for six nights in 2011 May. We employ a semiautomated pipeline to calibrate and reduce the images to the light curves that our group is developing for this purpose, which includes the differential photometry package DIAPL, written by Wozniak and modified by W. Pych. Several different diagnostics are employed for search of variability/transients. While no high-significance ML event was found in this observational run, we have detected more than 20 new variables and variable candidates in the M4 field, which we present here.

A First-look Atmospheric Modeling Study of the Young Directly Imaged Planet-mass Companion, ROXs 42Bb

NASA Astrophysics Data System (ADS)

Currie, Thayne; Burrows, Adam; Daemgen, Sebastian

2014-06-01

We present and analyze JKsL' photometry and our previously published H-band photometry and K-band spectroscopy for ROXs 42Bb, an object Currie et al. first reported as a young directly imaged planet-mass companion. ROXs 42Bb exhibits IR colors redder than field L dwarfs but consistent with other planet-mass companions. From the H2O-2 spectral index, we estimate a spectral type of L0 ± 1; weak detections/non-detections of the CO bandheads, Na I, and Ca I support evidence for a young, low surface gravity object primarily derived from the H2(K) index. ROXs 42Bb's photometry/K-band spectrum are inconsistent with limiting cases of dust-free atmospheres (COND) and marginally inconsistent with the AMES/DUSTY models and the BT-SETTL models. However, ROXS 42Bb data are simultaneously fit by atmosphere models incorporating several micron-sized dust grains entrained in thick clouds, although further modifications are needed to better reproduce the K-band spectral shape. ROXs 42Bb's best-estimated temperature is T eff ~ 1950-2000 K, near the low end of the empirically derived range in Currie et al. For an age of ~1-3 Myr and considering the lifetime of the protostar phase, ROXs 42Bb's luminosity of log(L/L ⊙) ~ -3.07 ± 0.07 implies a mass of 9^{+3}_{-3} MJ , making it one of the lightest planetary-mass objects yet imaged.

The Influence of Very Low Illumination on the Postural Sway of Young and Elderly Adults

PubMed Central

Rugelj, Darja; Gomišček, Gregor; Sevšek, France

2014-01-01

The purpose of the present study was to evaluate the influence of very low ambient illumination and complete darkness on the postural sway of young and elderly adults. Eighteen healthy young participants aged 23.8±1.5 years and 26 community-dwelling elderly aged 69.8±5.6 years were studied. Each participant performed four tests while standing on a force platform in the following conditions: in normal light (215 lx) with open eyes and with closed eyes, in very low illumination (0.25 lx) with open eyes, and in complete darkness with open eyes. The sequences of the tests in the altered visual conditions were determined by random blocs. Postural sway was assessed by means of the force platform measurements. The centre of pressure variables: the medio-lateral and antero-posterior path lengths, mean velocities, sway areas, and fractal dimensions were analysed. Very low illumination resulted in a statistically significant increase in postural sway in both the young and elderly groups compared to normal light, although the increase was significantly smaller than those observed in the eyes closed and complete darkness condition, and no significant effects of illumination on fractal dimensions were detected. The gains of the sways in the very low or no illumination conditions relative to the normal light condition were significantly larger in the group of young participants than in the group of elderly participants (up to 50% and 25%, respectively). However, the response patterns to changes in illumination were similar in the young and elderly participants, with the exception of the short-range fractal dimension of the medio-lateral sway. In conclusion, very low illumination resulted in increased postural sway compared to normal illumination; however, in the closed eye and complete darkness conditions, postural sway was significantly higher than in the very low illumination condition regardless of the age of the participants. PMID:25084015

The Mass Function of Young Star Clusters in the "Antennae" Galaxies.

PubMed

Zhang; Fall

1999-12-20

We determine the mass function of young star clusters in the merging galaxies known as the "Antennae" (NGC 4038/9) from deep images taken with the Wide Field Planetary Camera 2 on the refurbished Hubble Space Telescope. This is accomplished by means of reddening-free parameters and a comparison with stellar population synthesis tracks to estimate the intrinsic luminosity and age, and hence the mass, of each cluster. We find that the mass function of the young star clusters (with ages less, similar160 Myr) is well represented by a power law of the form psi&parl0;M&parr0;~M-2 over the range 104 less, similarM less, similar106 M middle dot in circle. This result may have important implications for our understanding of the origin of globular clusters during the early phases of galactic evolution.

Family meals among New Zealand young people: relationships with eating behaviors and body mass index.

PubMed

Utter, Jennifer; Denny, Simon; Robinson, Elizabeth; Fleming, Terry; Ameratunga, Shanthi; Grant, Sue

2013-01-01

To examine the relationship between family meals and nutrition behaviors of adolescents. Secondary analysis of Youth'07, a nationally representative survey. Secondary schools in New Zealand. Randomly selected adolescents (aged 13-17 years, n = 9,107) completed a multimedia and anonymous survey about their health. Body mass index and eating behaviors. Multiple logistic regression equations were used to determine the associations between family meals and body size and dietary behaviors, controlling for demographic variables. Nearly 60% of young people shared a meal with their families 5 or more times in the previous week. Frequent family meals were associated with greater consumption of fruits and vegetables (P < .001), and breakfast (P < .001). Adolescents who frequently shared family meals were also more likely to report that what they ate in the past week was healthy than adolescents who did not (P < .001). There was no relationship between frequency of family meals and body mass index (P = .60). Data from the current study suggest that family meals cannot be used as a single strategy for obesity prevention, but they may provide an important opportunity for young people to consume healthy food. Copyright © 2013 Society for Nutrition Education and Behavior. Published by Elsevier Inc. All rights reserved.

The Prototypical Young L/T-Transition Dwarf HD 203030B Likely Has Planetary Mass

NASA Astrophysics Data System (ADS)

Miles-Páez, Paulo A.; Metchev, Stanimir; Luhman, Kevin L.; Marengo, Massimo; Hulsebus, Alan

2017-12-01

Upon its discovery in 2006, the young L7.5 companion to the solar analog HD 203030 was found to be ≈ 200 K cooler than older late-L dwarfs, which is quite unusual. HD 203030B offered the first clear indication that the effective temperature at the L-to-T spectral type transition depends on surface gravity: now a well-known characteristic of low-gravity ultra-cool dwarfs. An initial age analysis of the G8V primary star indicated that the system was 130-400 Myr old, and so the companion would be between 12 and 31 {M}{Jup}. Using moderate-resolution near-infrared spectra of HD 203030B, we now find features of very low gravity comparable to those of 10-150 Myr old L7-L8 dwarfs. We also obtained more accurate near-infrared and Spitzer/IRAC photometry, and we find a {(J-K)}{MKO} color of 2.56 ± 0.13 mag—comparable to those observed in other young planetary-mass objects—and a luminosity of log({L}{bol}/{L}⊙ ) = -4.75 ± 0.04 dex. We further re-assess the evidence for the young age of the host star, HD 203030, with a more comprehensive analysis of the photometry and updated stellar activity measurements and age calibrations. Summarizing the age diagnostics for both components of the binary, we adopt an age of 100 Myr for HD 203030B and an age range of 30-150 Myr. Using cloudy evolutionary models, the new companion age range and luminosity result in a mass of 11 {M}{Jup} with a range of 8-15 {M}{Jup}, and an effective temperature of 1040 ± 50 K.

Anthropometric Variables and Somatotype of Young and Professional Male Basketball Players

PubMed Central

Kopiczko, Anna; Mikołajec, Kazimierz; Musalek, Martin

2018-01-01

Background: Determining somatic models and profiles in young athletes has recently become a fundamental element in selecting basketball playing positions. The aim of this study was to assess the relationship between the body build of young and adult elite male basketball players at different playing positions. Methods: Participants consisted of 35 young (age: 14.09 ± 0.30 years, n = 35) and 35 adult professional basketball players (age: 24.45 ± 5.40 years, n = 35) competing in elite leagues. The anthropometric characteristics assessed included body mass, body height, skinfolds, somatotypes, girths, and breadths. Results: The centers in both age groups were significantly taller and heavier (p < 0.001) compared to forwards and guards. The greatest difference between categories were in the guards’ personal height (from 169.36 to 186.68 = 17.32 cm). The guards from the professional team were closest in height to the forwards (difference = 7.17 cm) compared to young players where the difference between guards and forwards was 13.23 cm. Young competitors were more ectomorphic (2.12-3.75-4.17), while professional players were more mesomorphic (2.26-4.57-3.04). Significant criteria for center selection at professional level seems to be personal height and arm span ratio. Conclusions: The results indicate that the selection for basketball playing positions should include the analysis of body height and mass, shoulder breadth, humerus breadth, femur breadth and specifically for centers the difference between personal the height and arm span.

Anthropometric Variables and Somatotype of Young and Professional Male Basketball Players.

PubMed

Gryko, Karol; Kopiczko, Anna; Mikołajec, Kazimierz; Stasny, Petr; Musalek, Martin

2018-01-29

Determining somatic models and profiles in young athletes has recently become a fundamental element in selecting basketball playing positions. The aim of this study was to assess the relationship between the body build of young and adult elite male basketball players at different playing positions. Participants consisted of 35 young (age: 14.09 ± 0.30 years, n = 35) and 35 adult professional basketball players (age: 24.45 ± 5.40 years, n = 35) competing in elite leagues. The anthropometric characteristics assessed included body mass, body height, skinfolds, somatotypes, girths, and breadths. The centers in both age groups were significantly taller and heavier ( p < 0.001) compared to forwards and guards. The greatest difference between categories were in the guards' personal height (from 169.36 to 186.68 = 17.32 cm). The guards from the professional team were closest in height to the forwards (difference = 7.17 cm) compared to young players where the difference between guards and forwards was 13.23 cm. Young competitors were more ectomorphic (2.12-3.75-4.17), while professional players were more mesomorphic (2.26-4.57-3.04). Significant criteria for center selection at professional level seems to be personal height and arm span ratio. The results indicate that the selection for basketball playing positions should include the analysis of body height and mass, shoulder breadth, humerus breadth, femur breadth and specifically for centers the difference between personal the height and arm span.

Discovery of a wide planetary-mass companion to the young M3 star GU PSC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Naud, Marie-Eve; Artigau, Étienne; Malo, Lison

2014-05-20

We present the discovery of a comoving planetary-mass companion ∼42'' (∼2000 AU) from a young M3 star, GU Psc, a likely member of the young AB Doradus Moving Group (ABDMG). The companion was first identified via its distinctively red i – z color (>3.5) through a survey made with Gemini-S/GMOS. Follow-up Canada-France-Hawaii Telescope/WIRCam near-infrared (NIR) imaging, Gemini-N/GNIRS NIR spectroscopy and Wide-field Infrared Survey Explorer photometry indicate a spectral type of T3.5 ± 1 and reveal signs of low gravity which we attribute to youth. Keck/Adaptive Optics NIR observations did not resolve the companion as a binary. A comparison with atmospheremore » models indicates T {sub eff} = 1000-1100 K and log g = 4.5-5.0. Based on evolution models, this temperature corresponds to a mass of 9-13 M {sub Jup} for the age of ABDMG (70-130 Myr). The relatively well-constrained age of this companion and its very large angular separation to its host star will allow its thorough characterization and will make it a valuable comparison for planetary-mass companions that will be uncovered by forthcoming planet-finder instruments such as Gemini Planet Imager and SPHERE 9.« less

Mid-infrared interferometric variability of DG Tau: implications for the inner-disk structure .

NASA Astrophysics Data System (ADS)

Ábrahám, P.; Varga, J.; Gabányi, K. É.; Chen, L.; Kóspál, Á.; Ratzka, Th.; van Boekel, R.; Mosoni, L.; Henning, Th.

DG Tau is a low-mass young star whose strongly accreting disk shows a variable 10 mu m silicate feature, that may even turn temporarily from emission to absorption. Aiming to find the physical reason of this variability, we analysed multiepoch VLTI/MIDI interferometric observations. We found that the inner disk within 3 au radius exhibits a 10 mu m absorption feature related to amorphous silicate grains, while the outer disk displays a variable crystalline feature in emission, similar in shape to the spectrum of comet Hale-Bopp. The variability may be related to a fluctuating amount of dusty material above the disk surface, possibly due to turbulence.

Investigating the Prevalence of Low Bone Mass in Children of Southern Iran and Its Associated Factors

PubMed Central

Saki, Forough; Ranjbar Omrani, Gholamhossein; Jeddi, Marjan; Bakhshaieshkaram, Marzie; Dabbaghmanesh, Mohammad Hossein

2017-01-01

Background Improving peak bone mass and bone strength in the first years of life and enhancing it during young adulthood could prevent osteoporosis and fractures in the last years of life. We evaluated the prevalence of low bone mass in the lumbar and femoral neck and its associated factors in southern Iranian children. Methods This is a cross-sectional study on healthy Iranian children aged 9 - 18 years old during 2011 - 2012. Dual energy X-ray absorptiometry (DEXA) was used for measuring bone mineral density (BMD). BMD Z-score ≤ -2 was considered as low. Anthropometric data, physical activity, sun exposure, puberty, and mineral biochemical parameters were assessed. Data were analyzed using SPSS v.15. Results 477 normal children, including 236 (49.5%) girls and 241 (50.5%) boys, aged 13.8 ± 2.7 years were enrolled. Prevalence of low bone mass (LBM) in the femoral and lumbar region was 10.7% and 18.7%, respectively. The prevalence of LBM in femur of girls is twice more than boys. Fat mass index, BMI Z-score, and physical activity were associated with lumbar low bone mass. BMI Z-score and physical activity were associated with femoral low bone mass. Conclusions High prevalence of low bone mineral density in children 9 to 18 years in south of the country is concerned and is needed to plan for prevention and treatment. BMI-Z score, fat mass index, and physical activity were the 3 most important preventive factors in developing low bone mass in children. PMID:29344033

On the capability of SWARM for estimating time-variable gravity fields and mass variations

NASA Astrophysics Data System (ADS)

Reubelt, Tilo; Baur, Oliver; Weigelt, Matthias; Sneeuw, Nico

2013-04-01

Recently, the implementation of the GRACE Follow-On mission has been approved. However, this successor of GRACE is planned to become operational in 2017 at the earliest. In order to fill the impending gap of 3-4 years between GRACE and GRACE-FO, the capability of the magnetic field mission SWARM as a gap filler for time-variable gravity field determination has to be investigated. Since the three SWARM satellites, where two of them fly on a pendulum formation, are equipped with high-quality GPS receivers and accelerometers, orbit analysis from high-low Satellite-to-Satellite Tracking (hl-SST) can be applied for geopotential recovery. As data analysis from CHAMP and GRACE has shown, the detection of annual gravity signals and gravity trends from hl-SST is possible for long-wavelength features corresponding to a Gaussian radius of 1000 km, although the accuracy of a low-low SST mission like GRACE cannot be reached. However, since SWARM is a three-satellite constellation and might provide GPS data of higher quality compared to previous missions, improved gravity field recovery can be expected. We present detailed closed-loop simulation studies for a 5 years period based on time-variable gravity caused by mass changes in the hydrosphere, cryosphere and solid Earth. Models for these variations are used to simulate the SWARM satellite orbits. We recover time-variable gravity from orbit analysis adopting the acceleration approach. Finally, we convert time-variable gravity to mass change in order to compare with the a priori model input.

Arterial stiffness is associated to cardiorespiratory fitness and body mass index in young Swedish adults: The Lifestyle, Biomarkers, and Atherosclerosis study.

PubMed

Fernberg, Ulrika; Fernström, Maria; Hurtig-Wennlöf, Anita

2017-11-01

Background Early changes in the large muscular arteries are already associated with risk factors as hypertension and obesity in adolescence and young adulthood. The present study examines the association between arterial stiffness measurements, pulse wave velocity and augmentation index and lifestyle-related factors, body composition and cardiorespiratory fitness, in young, healthy, Swedish adults. Design This study used a population-based cross-sectional sample. Methods The 834 participants in the study were self-reported healthy, non-smoking, age 18-25 years. Augmentation index and pulse wave velocity were measured with applanation tonometry. Cardiorespiratory fitness was measured by ergometer bike test to estimate maximal oxygen uptake. Body mass index (kg/m 2 ) was calculated and categorised according to classification by the World Health Organisation. Results Young Swedish adults with obesity and low cardiorespiratory fitness have significantly higher pulse wave velocity and augmentation index than non-obese young adults with medium or high cardiorespiratory fitness. The observed U-shaped association between pulse wave velocity and body mass index categories in women indicates that it might be more beneficial to be normal weight than underweight when assessing the arterial stiffness with pulse wave velocity. The highest mean pulse wave velocity was found in overweight/obese individuals with low cardiorespiratory fitness. The lowest mean pulse wave velocity was found in normal weight individuals with high cardiorespiratory fitness. Cardiorespiratory fitness had a stronger effect than body mass index on arterial stiffness in multiple regression analyses. Conclusions The inverse association between cardiorespiratory fitness and arterial stiffness is observed already in young adults. The study result highlights the importance of high cardiorespiratory fitness, but also that underweight individuals may be a possible risk group that needs to be further studied.

Fundmental Parameters of Low-Mass Stars, Brown Dwarfs, and Planets

NASA Astrophysics Data System (ADS)

Montet, Benjamin; Johnson, John A.; Bowler, Brendan; Shkolnik, Evgenya

2016-01-01

Despite advances in evolutionary models of low-mass stars and brown dwarfs, these models remain poorly constrained by observations. In order to test these predictions directly, masses of individual stars must be measured and combined with broadband photometry and medium-resolution spectroscopy to probe stellar atmospheres. I will present results from an astrometric and spectroscopic survey of low-mass pre-main sequence binary stars to measure individual dynamical masses and compare to model predictions. This is the first systematic test of a large number of stellar systems of intermediate age between young star-forming regions and old field stars. Stars in our sample are members of the Tuc-Hor, AB Doradus, and beta Pictoris moving groups, the last of which includes GJ 3305 AB, the wide binary companion to the imaged exoplanet host 51 Eri. I will also present results of Spitzer observations of secondary eclipses of LHS 6343 C, a T dwarf transiting one member of an M+M binary in the Kepler field. By combining these data with Kepler photometry and radial velocity observations, we can measure the luminosity, mass, and radius of the brown dwarf. This is the first non-inflated brown dwarf for which all three of these parameters have been measured, providing the first benchmark to test model predictions of the masses and radii of field T dwarfs. I will discuss these results in the context of K2 and TESS, which will find additional benchmark transiting brown dwarfs over the course of their missions, including a description of the first planet catalog developed from K2 data and a program to search for transiting planets around mid-M dwarfs.

Simultaneous Multiwavelength Variability Characterization of the Free-floating Planetary-mass Object PSO J318.5‑22

NASA Astrophysics Data System (ADS)

Biller, Beth A.; Vos, Johanna; Buenzli, Esther; Allers, Katelyn; Bonnefoy, Mickaël; Charnay, Benjamin; Bézard, Bruno; Allard, France; Homeier, Derek; Bonavita, Mariangela; Brandner, Wolfgang; Crossfield, Ian; Dupuy, Trent; Henning, Thomas; Kopytova, Taisiya; Liu, Michael C.; Manjavacas, Elena; Schlieder, Joshua

2018-02-01

We present simultaneous Hubble Space Telescope (HST) WFC3+Spitzer IRAC variability monitoring for the highly variable young (∼20 Myr) planetary-mass object PSO J318.5‑22. Our simultaneous HST + Spitzer observations covered approximately two rotation periods with Spitzer and most of a rotation period with the HST. We derive a period of 8.6 ± 0.1 hr from the Spitzer light curve. Combining this period with the measured v\\sin i for this object, we find an inclination of 56.°2 ± 8.°1. We measure peak-to-trough variability amplitudes of 3.4% ± 0.1% for Spitzer Channel 2 and 4.4%–5.8% (typical 68% confidence errors of ∼0.3%) in the near-IR bands (1.07–1.67 μm) covered by the WFC3 G141 prism—the mid-IR variability amplitude for PSO J318.5‑22 is one of the highest variability amplitudes measured in the mid-IR for any brown dwarf or planetary-mass object. Additionally, we detect phase offsets ranging from 200° to 210° (typical error of ∼4°) between synthesized near-IR light curves and the Spitzer mid-IR light curve, likely indicating depth-dependent longitudinal atmospheric structure in this atmosphere. The detection of similar variability amplitudes in wide spectral bands relative to absorption features suggests that the driver of the variability may be inhomogeneous clouds (perhaps a patchy haze layer over thick clouds), as opposed to hot spots or compositional inhomogeneities at the top-of-atmosphere level.

Complex organic molecules during low-mass star formation: Pilot survey results

DOE Office of Scientific and Technical Information (OSTI.GOV)

Öberg, Karin I.; Graninger, Dawn; Lauck, Trish, E-mail: koberg@cfa.harvard.edu

Complex organic molecules (COMs) are known to be abundant toward some low-mass young stellar objects (YSOs), but how these detections relate to typical COM abundance are not yet understood. We aim to constrain the frequency distribution of COMs during low-mass star formation, beginning with this pilot survey of COM lines toward six embedded YSOs using the IRAM 30 m Telescope. The sample was selected from the Spitzer c2d ice sample and covers a range of ice abundances. We detect multiple COMs, including CH{sub 3}CN, toward two of the YSOs, and tentatively toward a third. Abundances with respect to CH{sub 3}OHmore » vary between 0.7% and 10%. This sample is combined with previous COM observations and upper limits to obtain a frequency distributions of CH{sub 3}CN, HCOOCH{sub 3}, CH{sub 3}OCH{sub 3}, and CH{sub 3}CHO. We find that for all molecules more than 50% of the sample have detections or upper limits of 1%-10% with respect to CH{sub 3}OH. Moderate abundances of COMs thus appear common during the early stages of low-mass star formation. A larger sample is required, however, to quantify the COM distributions, as well as to constrain the origins of observed variations across the sample.« less

Local dynamic stability and gait variability during attentional tasks in young adults.

PubMed

Magnani, Rina Márcia; Lehnen, Georgia Cristina; Rodrigues, Fábio Barbosa; de Sá E Souza, Gustavo Souto; de Oliveira Andrade, Adriano; Vieira, Marcus Fraga

2017-06-01

Cell phone use while walking may be a cognitive distraction and reduce visual and motor attention. Thus, the aim of this study was to verify the effects of attentional dual-tasks while using a cell phone in different conditions. Stability, regularity, and linear variability of trunk kinematics, and gait spatiotemporal parameters in young adults were measured. Twenty young subjects of both genders were asked to walk on a treadmill for 4min under the following conditions: (a) looking forward at a fixed target 2.5m away (walking); (b) talking on a cell phone with unilateral handling (talking); (c) texting messages on a cell phone with unilateral handling (texting); and (d) looking forward at the aforementioned target while listening to music without handling the phone (listening). Local dynamic stability measured in terms of the largest Lyapunov exponent decreased while handling a cell phone (talking and texting). Gait variability and regularity increased when talking on a cell phone, but no variable changed in the listening condition. Under all dual-task conditions, there were significant increases in stride width and its variability. We conclude that young adults who use a cell phone when walking adapt their gait pattern conservatively, which can be because of increased attentional demand during cell phone use. Copyright © 2017 Elsevier B.V. All rights reserved.

NEW EXTINCTION AND MASS ESTIMATES FROM OPTICAL PHOTOMETRY OF THE VERY LOW MASS BROWN DWARF COMPANION CT CHAMAELEONTIS B WITH THE MAGELLAN AO SYSTEM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Ya-Lin; Close, Laird M.; Males, Jared R.

We used the Magellan adaptive optics system and its VisAO CCD camera to image the young low mass brown dwarf companion CT Chamaeleontis B for the first time at visible wavelengths. We detect it at r', i', z', and Y{sub S}. With our new photometry and T {sub eff} ∼ 2500 K derived from the shape of its K-band spectrum, we find that CT Cha B has A{sub V} = 3.4 ± 1.1 mag, and a mass of 14-24 M{sub J} according to the DUSTY evolutionary tracks and its 1-5 Myr age. The overluminosity of our r' detection indicates thatmore » the companion has significant Hα emission and a mass accretion rate ∼6 × 10{sup –10} M {sub ☉} yr{sup –1}, similar to some substellar companions. Proper motion analysis shows that another point source within 2'' of CT Cha A is not physical. This paper demonstrates how visible wavelength adaptive optics photometry (r', i', z', Y{sub S}) allows for a better estimate of extinction, luminosity, and mass accretion rate of young substellar companions.« less

New Extinction and Mass Estimates from Optical Photometry of the Very Low Mass Brown Dwarf Companion CT Chamaeleontis B with the Magellan AO System

NASA Astrophysics Data System (ADS)

Wu, Ya-Lin; Close, Laird M.; Males, Jared R.; Barman, Travis S.; Morzinski, Katie M.; Follette, Katherine B.; Bailey, Vanessa; Rodigas, Timothy J.; Hinz, Philip; Puglisi, Alfio; Xompero, Marco; Briguglio, Runa

2015-03-01

We used the Magellan adaptive optics system and its VisAO CCD camera to image the young low mass brown dwarf companion CT Chamaeleontis B for the first time at visible wavelengths. We detect it at r', i', z', and YS . With our new photometry and T eff ~ 2500 K derived from the shape of its K-band spectrum, we find that CT Cha B has AV = 3.4 ± 1.1 mag, and a mass of 14-24 MJ according to the DUSTY evolutionary tracks and its 1-5 Myr age. The overluminosity of our r' detection indicates that the companion has significant Hα emission and a mass accretion rate ~6 × 10-10 M ⊙ yr-1, similar to some substellar companions. Proper motion analysis shows that another point source within 2'' of CT Cha A is not physical. This paper demonstrates how visible wavelength adaptive optics photometry (r', i', z', YS ) allows for a better estimate of extinction, luminosity, and mass accretion rate of young substellar companions. This paper includes data gathered with the 6.5 m Magellan Clay Telescope at Las Campanas Observatory, Chile.

Suppressed Far-UV Stellar Activity and Low Planetary Mass Loss in the WASP-18 System

NASA Astrophysics Data System (ADS)

Fossati, L.; Koskinen, T.; France, K.; Cubillos, P. E.; Haswell, C. A.; Lanza, A. F.; Pillitteri, I.

2018-03-01

WASP-18 hosts a massive, very close-in Jupiter-like planet. Despite its young age (<1 Gyr), the star presents an anomalously low stellar activity level: the measured {log}{R}HK}{\\prime } activity parameter lies slightly below the basal level; there is no significant time-variability in the {log}{R}HK}{\\prime } value; there is no detection of the star in the X-rays. We present results of far-UV observations of WASP-18 obtained with COS on board of Hubble Space Telescope aimed at explaining this anomaly. From the star’s spectral energy distribution, we infer the extinction (E(B-V) ≈ 0.01 mag) and then the interstellar medium (ISM) column density for a number of ions, concluding that ISM absorption is not the origin of the anomaly. We measure the flux of the four stellar emission features detected in the COS spectrum (C II, C III, C IV, Si IV). Comparing the C II/C IV flux ratio measured for WASP-18 with that derived from spectra of nearby stars with known age, we see that the far-UV spectrum of WASP-18 resembles that of old (>5 Gyr), inactive stars, in stark contrast with its young age. We conclude that WASP-18 has an intrinsically low activity level, possibly caused by star–planet tidal interaction, as suggested by previous studies. Re-scaling the solar irradiance reference spectrum to match the flux of the Si IV line, yields an XUV integrated flux at the planet orbit of 10.2 erg s‑1 cm‑2. We employ the rescaled XUV solar fluxes to models of the planetary upper atmosphere, deriving an extremely low thermal mass-loss rate of 10‑20 M J Gyr‑1. For such high-mass planets, thermal escape is not energy limited, but driven by Jeans escape. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from MAST at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program #13859. Based on

An effective selection method for low-mass active black holes and first spectroscopic identification

NASA Astrophysics Data System (ADS)

Morokuma, Tomoki; Tominaga, Nozomu; Tanaka, Masaomi; Yasuda, Naoki; Furusawa, Hisanori; Taniguchi, Yuki; Kato, Takahiro; Jiang, Ji-an; Nagao, Tohru; Kuncarayakti, Hanindyo; Morokuma-Matsui, Kana; Ikeda, Hiroyuki; Blinnikov, Sergei; Nomoto, Ken'ichi; Kokubo, Mitsuru; Doi, Mamoru

2016-06-01

We present a new method for effectively selecting objects which may be low-mass active black holes (BHs) at galaxy centers using high-cadence optical imaging data, and our first spectroscopic identification of an active 2.7 × 106 M⊙ BH at z = 0.164. This active BH was originally selected due to its rapid optical variability, from a few hours to a day, based on Subaru Hyper Suprime-Cam g-band imaging data taken with a 1 hr cadence. Broad and narrow Hα lines and many other emission ones are detected in our optical spectra taken with Subaru FOCAS, and the BH mass is measured via the broad Hα emission line width (1880 km s-1) and luminosity (4.2 × 1040 erg s-1) after careful correction to the atmospheric absorption around 7580-7720 Å. We measure the Eddington ratio and find it to be as low as 0.05, considerably smaller than those in a previous SDSS sample with similar BH mass and redshift, which indicates one of the special potentials of our Subaru survey. The g - r color and morphology of the extended component indicate that the host galaxy is a star-forming galaxy. We also show the effectiveness of our variability selection for low-mass active BHs.

Development of a non-piston MR suspension rod for variable mass systems

NASA Astrophysics Data System (ADS)

Deng, Huaxia; Han, Guanghui; Zhang, Jin; Wang, Mingxian; Ma, Mengchao; Zhong, Xiang; Yu, Liandong

2018-06-01

The semi-active suspension systems for variable mass systems require long work stroke and variable damping, while the currently piston structure limits the work stroke for the magnetorheological (MR) dampers. The main work of this paper is to design a semi-active non-piston MR (NPMR) suspension rod for the reduction of the vibration of an automatic impeller washing machine, which is a typical variable mass system. The designed suspension rod locates in the suspension system that links the internal tub to the washing machine cabinet. The NPMR suspension rod includes a MR part and a air part. The MR part can provide low initial damping force and the unlimited work stroke compared with the piston MR damper. The hysteretic response tests and vibration performance evaluation with different loadings are conducted to verify the dynamic performance for the designed rod. The measured damping force of the MR part varies from 5 to 20 N. Studies of dehydration mode experiments of the washing machine indicate that its vibration acceleration with the NPMR suspension rods can reduce to half of the original passive ones in certain conditions.

Dark-Spot Activity on the Secondary as the Origin of Variable Mass Accretion in Cataclysmic Variables

NASA Astrophysics Data System (ADS)

Qian, S.-B.; Zhu, L.-Y.; Fernández-Lajús, E.; He, J.-J.; Liao, W.-P.; Zhao, E.-G.; Liu, L.; Yang, Y.-G.

2014-08-01

In magnetic CVs (polars), the magnetic fields of the white dwarfs are strong enough to prevent materials from the main-sequence companions for forming an accretion disc. Therefore, polars especially eclipsing polars provide a good chance to study mass accretion directly. In the past 4 years, we have monitored several eclipsing polars (e.g., DP Leo and HU Aqr) by using the 2.4-m and 1.0-m telescopes in China and the 2.15-m telescope in Argentina. Nearly 100 eclipse profiles were obtained. In this talk, apart from the detection of a few giant planets orbiting polars, I will summarize some other progresses of our research group at Yunnan Observatories. Our results are as following: (1) the correlation between the out-of-eclipse brightness variation and the change of the eclipse profile suggests that both the accretion hot spot and the accretion stream brighten and become faint instantaneously. This is the direct evidence of variable mass transfer in a CV that is also supported by the relation between the out-of-eclipse brightness and the depth of eclipse. (2) We find the brightness state change is correlated with the dark-spot activity near the L1 point. The low state usually corresponds to the presence of a large spot at L1 point, while the dark spot disappear at a high state indicating that it is the dark-spot activity caused the mass transfer in CVs. (3) Magnetic activity cycles of the cool secondary did not correlate with the brightness state change revealing the variable mass accretion was not caused by magnetic activity cycles.

Identification of young stellar variables with KELT for K2 - II. The Upper Scorpius association

NASA Astrophysics Data System (ADS)

Ansdell, Megan; Oelkers, Ryan J.; Rodriguez, Joseph E.; Gaidos, Eric; Somers, Garrett; Mamajek, Eric; Cargile, Phillip A.; Stassun, Keivan G.; Pepper, Joshua; Stevens, Daniel J.; Beatty, Thomas G.; Siverd, Robert J.; Lund, Michael B.; Kuhn, Rudolf B.; James, David; Gaudi, B. Scott

2018-01-01

High-precision photometry from space-based missions such as K2 and Transiting Exoplanet Survey Satellite enables detailed studies of young star variability. However, because space-based observing campaigns are often short (e.g. 80 d for K2), complementary long-baseline photometric surveys are critical for obtaining a complete understanding of young star variability, which can change on time-scales of minutes to years. We therefore present and analyse light curves of members of the Upper Scorpius association made over 5.5 yr by the ground-based Kilodegree Extremely Little Telescope (KELT), which complement the high-precision observations of this region taken by K2 during its Campaigns 2 and 15. We show that KELT data accurately identify the periodic signals found with high-precision K2 photometry, demonstrating the power of ground-based surveys in deriving stellar rotation periods of young stars. We also use KELT data to identify sources exhibiting variability that is likely related to circumstellar material and/or stellar activity cycles; these signatures are often unseen in the short-term K2 data, illustrating the importance of long-term monitoring surveys for studying the full range of young star variability. We provide the KELT light curves as electronic tables in an ongoing effort to establish legacy time series data sets for young stellar clusters.

On the Existence of Low-Luminosity Cataclysmic Variables Beyond the Orbital Period Minimum

NASA Technical Reports Server (NTRS)

Howell, Steve B.; Rappaport, Saul; Politano, Michael

1997-01-01

Models of the present-day intrinsic population of cataclysmic variables predict that 99 per cent of these systems should be of short orbital period. The Galaxy is old enough that approx. 70 per cent of these stars will have already reached their orbital period minimum (approx. 80 min), and should be evolving back toward longer periods. Mass-transfer rates in these highly evolved binaries are predicted to be less or equal to 10(exp -11), leading to M(sub V) of approx. 10 or fainter, and the secondaries would be degenerate, brown dwarf-like stars. Recent observations of a group of low-luminosity dwarf novae (TOADS) provide observational evidence for systems with very low intrinsic M,. and possibly low-mass secondaries. We carry out population synthesis and evolution calculations for a range of assumed ages of the Galaxy in order to study P(sub orb) and M distributions for comparison with the TOAD observations. We speculate that at least some of the TOADs are the predicted very low- luminosity, post-period-minimum cataclysmic variables containing degenerate (brown dwarf-like) secondaries having masses between 0.02 and 0.06 M, and radii near 0.1 R., We show that these low-luminosity systems are additionally interesting in that they can be used to set a lower limit on the age of the Galaxy. The TOAD with the longest orbital period currently known (123 min), corresponds to a Galaxy age of at least 8.6 x 10(exp 9) yr.

Determining the cut-off point of osteoporosis based on the osteoporosis self-assessment tool, body mass index and weight in Taiwanese young adult women.

PubMed

Chang, Shu Fang; Yang, Rong Sen

2014-09-01

To examine the cut-off point of the osteoporosis self-assessment tool, age, weight and body mass index for osteoporosis among young adult Taiwanese women, using a large-scale health examination database containing bone mineral density tests. The cut-off points of osteoporosis risk factors identified earlier focus on menopausal or senior Caucasian and Asian women. However, young adult Asian women have seldom been identified. A retrospective historical cohort study. Using the 2009-2011 health examination database of a large-scale medical centre in northern Taiwan, this study investigated young adult Asian women (i.e. range in age from 30-49 years) in Taiwan who had received dual-energy X-ray absorptiometry test. This study also explored the cut-off point, sensitivity, specificity and diagnostic accuracy of receiver operating characteristics of osteoporosis among young adult females in Taiwan. This study collected 2454 young adult Asian women in Taiwan. Cochran-Armitage analysis results indicated that the prevalence of osteoporosis increased with decreasing weight, body mass index and osteoporosis self-assessment method quartiles. According to the results of receiver operating characteristics, weight, body mass index and osteoporosis self-assessment tool approaches can generally be used as indicators to predict osteoporosis among young adult Asian women. Results of this study demonstrate that Taiwanese women contracting osteoporosis tend to be young and underweight, as well as having a low body mass index and osteoporosis self-assessment scores. Those results further suggest that the assessment indicators for cut-off points are appropriately suitable for young adult women in Taiwan. Early detection is the only available means of preventing osteoporosis. Professional nurses should apply convenient and accurate assessment procedures to help young adult women to adopt preventive strategies against osteoporosis early, thus eliminating the probability of osteoporotic

A Prospective Comparison Study of Heart Rate Variability During Menses in Young Women With Dysmenorrhea.

PubMed

Wang, Yu-Jen; Wang, Yi-Zen; Yeh, Mei-Ling

2016-07-01

Numerous studies have demonstrated autonomic abnormalities in various pain conditions. However, few have investigated heart rate variability (HRV) in young women with primary dysmenorrhea, and the conclusions have been inconsistent. More evidence is required to confirm the reported trend for consistent fluctuation of HRV parameters in dysmenorrhea. The study's aim was to determine whether significant differences exist between young women with and without dysmenorrhea for heart rate (HR), blood pressure (BP), and HRV parameters during menses. A prospective comparison design with repeated measures was used. Sixty-six women aged 18-25 with dysmenorrhea and 54 eumenorrheic women were recruited from a university in northern Taiwan. High-frequency and low-frequency HRV parameters (HF and LF), LF/HF ratio, BP, and HR were measured daily between 8 p.m. and 10 p.m. from Day 1 to Day 6 during menses. The generalized estimating equation was used to analyze the effects of group, time, and Group × Time interaction on these variables. HF values were significantly lower in the dysmenorrhea than in the eumenorrhea group, but there were no differences in BP, HR, LF, or LF/HF ratio. Reduced HF values reflect reduced parasympathetic activity and autonomic instability in young women with dysmenorrhea. Future longitudinal studies are warranted to examine autonomic regulation in menstrual pain of varying intensities associated with dysmenorrhea-related symptoms and to clarify the causal relationship between dysmenorrhea and HRV fluctuations. © The Author(s) 2016.

Investigating Young Children's Learning of Mass Measurement

ERIC Educational Resources Information Center

Cheeseman, Jill; McDonough, Andrea; Ferguson, Sarah

2014-01-01

This paper reports results of a design experiment regarding young children's concepts of mass measurement. The research built on an earlier study in which a framework of "growth points" in early mathematics learning and a related, task-based, one-to-one interview to assess children's understanding of the measurement of mass…

The turbulent mean-flow, Reynolds-stress, and heat flux equations in mass-averaged dependent variables

NASA Technical Reports Server (NTRS)

Rubesin, M. W.; Rose, W. C.

1973-01-01

The time-dependent, turbulent mean-flow, Reynolds stress, and heat flux equations in mass-averaged dependent variables are presented. These equations are given in conservative form for both generalized orthogonal and axisymmetric coordinates. For the case of small viscosity and thermal conductivity fluctuations, these equations are considerably simpler than the general Reynolds system of dependent variables for a compressible fluid and permit a more direct extension of low speed turbulence modeling to computer codes describing high speed turbulence fields.

Effect of BMI, Body Fat Percentage and Fat Free Mass on Maximal Oxygen Consumption in Healthy Young Adults.

PubMed

Mondal, Himel; Mishra, Snigdha Prava

2017-06-01

Maximal oxygen consumption (VO 2max ) is an important measure of cardiorespiratory capacity of an individual at a given degree of fitness and oxygen availability. Risk of cardiovascular diseases increases with increasing degree of obesity and a low level of VO 2max has been established as an independent risk factor for cardiovascular mortality. To determine VO 2max in young adults and to find its correlation with Body Mass Index (BMI), Body Fat% and Fat Free Mass (FFM). Fifty four (male=30, female=24) healthy young adults of age group18-25 years after screening by Physical Activity Readiness Questionnaire (PAR-Q) participated in the study. Height was measured by stadiometer. Weight was measured by digital weighing scale with 0.1 kg sensitivity. Body fat% was measured by Bioelectrical Impedance Analysis (BIA) method. FFM was calculated by subtracting fat mass from the body weight. VO 2max (mL.kg -1 .min -1 ) was obtained by Submaximal Exercise Test (SET) by first two stages of Bruce Protocol with the basis of linear relationship between Heart Rate (HR) and oxygen consumption (VO 2 ). Data were analysed statistically in GraphPad Prism software version 6.01 for windows. VO 2max (mL.kg -1 .min -1 ) of male (43.25±7.25) was significantly (p<0.001) higher than female (31.65±2.10). BMI showed weak negative correlation (r= -0.3232, p=0.0171) with VO 2max but Body Fat% showed strong negative correlation (r= -0.7505, p<0.001) with VO 2max . FFM positively correlated (r=0.3727, p=0.0055) with VO 2max . Increased body fat is associated with decreased level of VO 2max in young adults. Obesity in terms of Fat% is a better parameter than BMI for prediction of low VO 2max .

Basin-scale heterogeneity in Antarctic precipitation and its impact on surface mass variability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fyke, Jeremy; Lenaerts, Jan T. M.; Wang, Hailong

Annually averaged precipitation in the form of snow, the dominant term of the Antarctic Ice Sheet surface mass balance, displays large spatial and temporal variability. Here we present an analysis of spatial patterns of regional Antarctic precipitation variability and their impact on integrated Antarctic surface mass balance variability simulated as part of a preindustrial 1800-year global, fully coupled Community Earth System Model simulation. Correlation and composite analyses based on this output allow for a robust exploration of Antarctic precipitation variability. We identify statistically significant relationships between precipitation patterns across Antarctica that are corroborated by climate reanalyses, regional modeling and icemore » core records. These patterns are driven by variability in large-scale atmospheric moisture transport, which itself is characterized by decadal- to centennial-scale oscillations around the long-term mean. We suggest that this heterogeneity in Antarctic precipitation variability has a dampening effect on overall Antarctic surface mass balance variability, with implications for regulation of Antarctic-sourced sea level variability, detection of an emergent anthropogenic signal in Antarctic mass trends and identification of Antarctic mass loss accelerations.« less

Basin-scale heterogeneity in Antarctic precipitation and its impact on surface mass variability

DOE PAGES

Fyke, Jeremy; Lenaerts, Jan T. M.; Wang, Hailong

2017-11-15

Annually averaged precipitation in the form of snow, the dominant term of the Antarctic Ice Sheet surface mass balance, displays large spatial and temporal variability. Here we present an analysis of spatial patterns of regional Antarctic precipitation variability and their impact on integrated Antarctic surface mass balance variability simulated as part of a preindustrial 1800-year global, fully coupled Community Earth System Model simulation. Correlation and composite analyses based on this output allow for a robust exploration of Antarctic precipitation variability. We identify statistically significant relationships between precipitation patterns across Antarctica that are corroborated by climate reanalyses, regional modeling and icemore » core records. These patterns are driven by variability in large-scale atmospheric moisture transport, which itself is characterized by decadal- to centennial-scale oscillations around the long-term mean. We suggest that this heterogeneity in Antarctic precipitation variability has a dampening effect on overall Antarctic surface mass balance variability, with implications for regulation of Antarctic-sourced sea level variability, detection of an emergent anthropogenic signal in Antarctic mass trends and identification of Antarctic mass loss accelerations.« less

Characterizing spatial and temporal variability of dissolved gases in aquatic environments with in situ mass spectrometry.

PubMed

Camilli, Richard; Duryea, Anthony N

2009-07-01

The TETHYS mass spectrometer is intended for long-term in situ observation of dissolved gases and volatile organic compounds in aquatic environments. Its design maintains excellent low mass range sensitivity and stability during long-term operations, enabling characterization of low-frequency variability in many trace dissolved gases. Results are presented from laboratory trials and a 300-h in situ trial in a shallow marine embayment in Massachusetts, U.S.A. This time series consists of over 15000 sample measurements and represents the longest continuous record made by an in situ mass spectrometer in an aquatic environment. These measurements possess sufficient sampling density and duration to apply frequency analysis techniques for study of temporal variability in dissolved gases. Results reveal correlations with specific environmental periodicities. Numerical methods are presented for converting mass spectrometer ion peak ratios to absolute-scale dissolved gas concentrations across wide temperature regimes irrespective of ambient pressure, during vertical water column profiles in a hypoxic deep marine basin off the coast of California, U.S.A. Dissolved oxygen concentration values obtained with the TETHYS instrument indicate close correlation with polarographic oxygen sensor data across the entire depth range. These methods and technology enable observation of aquatic environmental chemical distributions and dynamics at appropriate scales of resolution.

Variability Selected Low-Luminosity Active Galactic Nuclei in the 4 Ms Chandra Deep Field-South

NASA Technical Reports Server (NTRS)

Young, M.; Brandt, W. N.; Xue, Y. Q.; Paolillo, D. M.; Alexander, F. E.; Bauer, F. E.; Lehmer, B. D.; Luo, B.; Shemmer, O.; Schneider, D. P.;

BANYAN. IV. Fundamental parameters of low-mass star candidates in nearby young stellar kinematic groups—isochronal age determination using magnetic evolutionary models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malo, Lison; Doyon, René; Albert, Loïc

2014-09-01

Based on high-resolution optical spectra obtained with ESPaDOnS at Canada-France-Hawaii Telescope, we determine fundamental parameters (T {sub eff}, R, L {sub bol}, log g, and metallicity) for 59 candidate members of nearby young kinematic groups. The candidates were identified through the BANYAN Bayesian inference method of Malo et al., which takes into account the position, proper motion, magnitude, color, radial velocity, and parallax (when available) to establish a membership probability. The derived parameters are compared to Dartmouth magnetic evolutionary models and field stars with the goal of constraining the age of our candidates. We find that, in general, low-mass starsmore » in our sample are more luminous and have inflated radii compared to older stars, a trend expected for pre-main-sequence stars. The Dartmouth magnetic evolutionary models show a good fit to observations of field K and M stars, assuming a magnetic field strength of a few kG, as typically observed for cool stars. Using the low-mass members of the β Pictoris moving group, we have re-examined the age inconsistency problem between lithium depletion age and isochronal age (Hertzspring-Russell diagram). We find that the inclusion of the magnetic field in evolutionary models increases the isochronal age estimates for the K5V-M5V stars. Using these models and field strengths, we derive an average isochronal age between 15 and 28 Myr and we confirm a clear lithium depletion boundary from which an age of 26 ± 3 Myr is derived, consistent with previous age estimates based on this method.« less

The early phase of the SMBH-galaxy coevolution in low-z "young" galaxies

NASA Astrophysics Data System (ADS)

Nagao, Tohru

2014-01-01

It is now widely recognized that most galaxies have a supermassive black hole (SMBH) in their nucleus, and the evolution of SMBHs is closely related with that of their host galaxies (the SMBH-galaxy coevolution). This is suggested by the correlation in the mass of SMBHs and their host galaxies, that has been observed in low redshifts. However, the physics of the coevolution is totally unclear, that prevents us from complete understandings of the galaxy evolution. One possible strategy to tackle this issue is measuring the mass ratio between SMBHs and their host galaxies (M_BH/M_host) at high redshifs, since different scenarios predict different evolution of the ratio ofMBH/Mhost. However it is extremely challenging to measure the mass of the host of high-z quasars, given the faint surface brightness of the host at close to the glaring quasar nucleus. Here we propose a brand-new approach to assess the early phase of the SMBH-galaxy coevolution, by focusing on low-z AGN-hosting "young" galaxies. Specifically, we focus on some very metal-poor galaxies with broadline Balmer lines at z ~ 0.1 - 0.3. By examining the SMBH scaling relations in some low-z metal-poor AGNs through high-resolution IRCS imaging observations, we will discriminate various scenarios for the SMBH-galaxy coevolution.

Intraindividual Variability Is a Fundamental Phenomenon of Aging: Evidence from an 8-Year Longitudinal Study across Young, Middle, and Older Adulthood

ERIC Educational Resources Information Center

Bielak, Allison A. M.; Cherbuin, Nicolas; Bunce, David; Anstey, Kaarin J.

2014-01-01

Moment-to-moment intraindividual variability (IIV) in cognitive speed is a sensitive behavioral indicator of the integrity of the aging brain and brain damage, but little information is known about how IIV changes from being relatively low in young adulthood to substantially higher in older adulthood. We evaluated possible age group, sex, and task…

Flow of sand and a variable mass Atwood machine

NASA Astrophysics Data System (ADS)

Flores, José; Solovey, Guillermo; Gil, Salvador

2003-07-01

We discuss a simple and inexpensive apparatus that lets us measure the instantaneous flow rate of granular media, such as sand, in real time. The measurements allow us to elucidate the phenomenological laws that govern the flow of granular media through an aperture. We use this apparatus to construct a variable mass system and study the motion of an Atwood machine with one weight changing in time in a controlled manner. The study illustrates Newton's second law for variable mass systems and lets us investigate the dependence of the flow rate on acceleration.

Hurdles in low k1 mass production

NASA Astrophysics Data System (ADS)

Yim, Donggyu; Yang, Hyunjo; Park, Chanha; Hong, Jongkyun; Choi, Jaeseung

2005-05-01

As the optical lithography pushes toward its theoretical resolution limit 0.25k1, the application of aggressive Resolution Enhancement Techniques (RETs) are required in order to ensure necessary resolution, sufficient process window, and reasonable MEEF in critical layers. When chip makers are adopting RETs in low k1 device, there are a lot of crucial factors to take into account in the development and mass production. Those hurdles are not only difficult to overcome but also highly risky to the company, which adopts low k1 mass production strategy. But, low k1 production strategy is very attractive to all chip makers, owing to improving production capacity and cost of ownership. So, low k1 technology has been investigated by many lithography engineers. Lots of materials have been introduced. Most of them are just in RnD level. In this study, low k1 mass production issues shall be introduced, mainly. The definition of low k1 in mass production shall be suggested. And, a lot of low_k1 issues shall be introduced, also. Most of them were investigated/experienced in RnD development stage and final mass production line. Low k1 mass production, is some what different from only RnD development.

X-shooter observations of low-mass stars in the η Chamaeleontis association

NASA Astrophysics Data System (ADS)

Rugel, Michael; Fedele, Davide; Herczeg, Gregory

2018-01-01

The nearby η Chamaeleontis association is a collection of 4-10 Myr old stars with a disk fraction of 35-45%. In this study, the broad wavelength coverage of VLT/X-shooter is used to measure the stellar and mass accretion properties of 15 low-mass stars in the η Chamaeleontis association. For each star, the observed spectrum is fitted with a non-accreting stellar template and an accretion spectrum obtained from assuming a plane-parallel hydrogen slab. Five of the eight stars with an IR disk excess show excess UV emission, indicating ongoing accretion. The accretion rates measured here are similar to those obtained from previous measurements of excess UV emission, but tend to be higher than past measurements from Hα modeling. The mass accretion rates are consistent with those of other young star forming regions. This work is based on observations made with ESO Telescopes at the Paranal Observatory under program ID 084.C-1095.

Dynamic characteristics of a variable-mass flexible missile: Dynamics of a two-stage variable-mass flexible rocket

NASA Technical Reports Server (NTRS)

Meirovitch, L.; Bankovskis, J.

1969-01-01

The dynamic characteristics of two-stage slender elastic body were investigated. The first stage, containing a solid-fuel rocket, possesses variable mass while the second stage, envisioned as a flexible case, contains packaged instruments of constant mass. The mathematical formulation was in terms of vector equations of motion transformed by a variational principle into sets of scalar differential equations in terms of generalized coordinates. Solutions to the complete equations were obtained numerically by means of finite difference techniques. The problem has been programmed in the FORTRAN 4 language and solved on an IBM 360/50 computer. Results for limited cases are presented showing the nature of the solutions.

The effect of starspots on the radii of low-mass pre-main-sequence stars

NASA Astrophysics Data System (ADS)

Jackson, R. J.; Jeffries, R. D.

2014-07-01

A polytropic model is used to investigate the effects of dark photospheric spots on the evolution and radii of magnetically active, low-mass (M < 0.5 M⊙), pre-main-sequence (PMS) stars. Spots slow the contraction along Hayashi tracks and inflate the radii of PMS stars by a factor of (1 - β)-N compared to unspotted stars of the same luminosity, where β is the equivalent covering fraction of dark starspots and N ≃ 0.45 ± 0.05. This is a much stronger inflation than predicted by Spruit & Weiss for main-sequence stars with the same β, where N ˜ 0.2-0.3. These models have been compared to radii determined for very magnetically active K- and M-dwarfs in the young Pleiades and NGC 2516 clusters, and the radii of tidally locked, low-mass eclipsing binary components. The binary components and zero-age main-sequence K-dwarfs have radii inflated by ˜10 per cent compared to an empirical radius-luminosity relation that is defined by magnetically inactive field dwarfs with interferometrically measured radii; low-mass M-type PMS stars, that are still on their Hayashi tracks, are inflated by up to ˜40 per cent. If this were attributable to starspots alone, we estimate that an effective spot coverage of 0.35 < β < 0.51 is required. Alternatively, global inhibition of convective flux transport by dynamo-generated fields may play a role. However, we find greater consistency with the starspot models when comparing the loci of active young stars and inactive field stars in colour-magnitude diagrams, particularly for the highly inflated PMS stars, where the large, uniform temperature reduction required in globally inhibited convection models would cause the stars to be much redder than observed.

Blueberry Galaxies: The Lowest Mass Young Starbursts

NASA Astrophysics Data System (ADS)

Yang, Huan; Malhotra, Sangeeta; Rhoads, James E.; Wang, Junxian

2017-09-01

Searching for extreme emission line galaxies allows us to find low-mass metal-poor galaxies that are good analogs of high redshift Lyα emitting galaxies. These low-mass extreme emission line galaxies are also potential Lyman-continuum leakers. Finding them at very low redshifts (z≲ 0.05) allows us to be sensitive to even lower stellar masses and metallicities. We report on a sample of extreme emission line galaxies at z≲ 0.05 (blueberry galaxies). We selected them from SDSS broadband images on the basis of their broadband colors and studied their properties with MMT spectroscopy. From the entire SDSS DR12 photometric catalog, we found 51 photometric candidates. We spectroscopically confirm 40 as blueberry galaxies. (An additional seven candidates are contaminants, and four remain without spectra.) These blueberries are dwarf starburst galaxies with very small sizes (<1 kpc) and very high ionization ([O III]/[O II] ˜ 10-60). They also have some of the lowest stellar masses ({log}(M/{M}⊙ )˜ 6.5{--}7.5) and lowest metallicities (7.1< 12+{log}({{O}}/{{H}})< 7.8) of starburst galaxies. Thus, they are small counterparts to green pea galaxies and high redshift Lyα emitting galaxies.

Evidence for Cluster to Cluster Variations in Low-mass Stellar Rotational Evolution

NASA Astrophysics Data System (ADS)

Coker, Carl T.; Pinsonneault, Marc; Terndrup, Donald M.

2016-12-01

The concordance model for angular momentum evolution postulates that star-forming regions and clusters are an evolutionary sequence that can be modeled with assumptions about protostar-disk coupling, angular momentum loss from magnetized winds that saturates in a mass-dependent fashion at high rotation rates, and core-envelope decoupling for solar analogs. We test this approach by combining established data with the large h Per data set from the MONITOR project and new low-mass Pleiades data. We confirm prior results that young low-mass stars can be used to test star-disk coupling and angular momentum loss independent of the treatment of internal angular momentum transport. For slow rotators, we confirm the need for star-disk interactions to evolve the ONC to older systems, using h Per (age 13 Myr) as our natural post-disk case. There is no evidence for extremely long-lived disks as an alternative to core-envelope decoupling. However, our wind models cannot evolve rapid rotators from h Per to older systems consistently, and we find that this result is robust with respect to the choice of angular momentum loss prescription. We outline two possible solutions: either there is cosmic variance in the distribution of stellar rotation rates in different clusters or there are substantially enhanced torques in low-mass rapid rotators. We favor the former explanation and discuss observational tests that could be used to distinguish them. If the distribution of initial conditions depends on environment, models that test parameters by assuming a universal underlying distribution of initial conditions will need to be re-evaluated.

Variables related to tobacco use among young adults: are there differences between males and females?

PubMed

Pederson, Linda L; Koval, John J; Chan, Stella S H; Zhang, Xiaohe

2007-02-01

We sought to determine the association of four categories (chunks) of variables: (1) demographic characteristics, (2) family and friends smoking and other drug use, (3) psychosocial factors and attitude, and (4) lifestyle factors to current smoking as compared to never smoking among Canadian young adults. A cohort of 1270 young adults, followed for 10 years, completed a self-administered questionnaire. In multivariable analyses, the best final model for both genders did not include the psychosocial and attitudinal categories, but did contain variables in the demographic, family and friends, and lifestyle categories. Interventions for reducing smoking among young adults may be similar for males and females, a conclusion that differs from conclusions based on findings from younger age groups.

Pre-main sequence variables in young cluster Stock 18

NASA Astrophysics Data System (ADS)

Sinha, Tirthendu; Sharma, Saurabh; Pandey, Rakesh; Pandey, Anil Kumar

2018-04-01

We have carried out multi-epoch deep I band photometry of the open cluster Stock 18 to search for variable stars in star forming regions. In the present study, we identified 65 periodic and 217 non-periodic variable stars. The periods of most of the periodic variables are between 2 hours to 15 days and their magnitude varies between 0.05 to 0.6 mag. We have derived spectral energy distributions for 48 probable pre-main sequence variables. Their average age and mass are 2.7 ± 0.3 Myrs and 2.7 ± 0.2 Mo, respectively.

The low-mass stellar population in the young cluster Tr 37. Disk evolution, accretion, and environment

NASA Astrophysics Data System (ADS)

Sicilia-Aguilar, Aurora; Kim, Jinyoung Serena; Sobolev, Andrej; Getman, Konstantin; Henning, Thomas; Fang, Min

2013-11-01

Aims: We present a study of accretion and protoplanetary disks around M-type stars in the 4 Myr-old cluster Tr 37. With a well-studied solar-type population, Tr 37 is a benchmark for disk evolution. Methods: We used low-resolution spectroscopy to identify and classify 141 members (78 new ones) and 64 probable members, mostly M-type stars. Hα emission provides information about accretion. Optical, 2MASS, Spitzer, and WISE data are used to trace the spectral energy distributions (SEDs) and search for disks. We construct radiative transfer models to explore the structures of full-disks, pre-transition, transition, and dust-depleted disks. Results: Including the new members and the known solar-type stars, we confirm that a substantial fraction (~2/5) of disks show signs of evolution, either as radial dust evolution (transition/pre-transition disks) or as a more global evolution (with low small-dust masses, dust settling, and weak/absent accretion signatures). Accretion is strongly dependent on the SED type. About half of the transition objects are consistent with no accretion, and dust-depleted disks have weak (or undetectable) accretion signatures, especially among M-type stars. Conclusions: The analysis of accretion and disk structure suggests a parallel evolution of dust and gas. We find several distinct classes of evolved disks, based on SED type and accretion status, pointing to different disk dispersal mechanisms and probably different evolutionary paths. Dust depletion and opening of inner holes appear to be independent processes: most transition disks are not dust-depleted, and most dust-depleted disks do not require inner holes. The differences in disk structure between M-type and solar-type stars in Tr 37 (4 Myr old) are not as remarkable as in the young, sparse, Coronet cluster (1-2 Myr old), suggesting that other factors, like the environment/interactions in each cluster, are likely to play an important role in the disk evolution and dispersal. Finally, we

Healthy lifestyle through young adulthood and the presence of low cardiovascular disease risk profile in middle age: the Coronary Artery Risk Development in (Young) Adults (CARDIA) study.

PubMed

Liu, Kiang; Daviglus, Martha L; Loria, Catherine M; Colangelo, Laura A; Spring, Bonnie; Moller, Arlen C; Lloyd-Jones, Donald M

2012-02-28

A low cardiovascular disease risk profile (untreated cholesterol <200 mg/dL, untreated blood pressure <120/<80 mm Hg, never smoking, and no history of diabetes mellitus or myocardial infarction) in middle age is associated with markedly better health outcomes in older age, but few middle-aged adults have this low risk profile. We examined whether adopting a healthy lifestyle throughout young adulthood is associated with the presence of the low cardiovascular disease risk profile in middle age. The Coronary Artery Risk Development in (Young) Adults (CARDIA) study sample consisted of 3154 black and white participants 18 to 30 years of age at year 0 (1985-1986) who attended the year 0, 7, and 20 examinations. Healthy lifestyle factors defined at years 0, 7, and 20 included average body mass index <25 kg/m(2), no or moderate alcohol intake, higher healthy diet score, higher physical activity score, and never smoking. Mean age (25 years) and percentage of women (56%) were comparable across groups defined by number of healthy lifestyle factors. The age-, sex-, and race-adjusted prevalences of low cardiovascular disease risk profile at year 20 were 3.0%, 14.6%, 29.5%, 39.2%, and 60.7% for people with 0 or 1, 2, 3, 4, and 5 healthy lifestyle factors, respectively (P for trend <0.0001). Similar graded relationships were observed for each sex-race group (all P for trend <0.0001). Maintaining a healthy lifestyle throughout young adulthood is strongly associated with a low cardiovascular disease risk profile in middle age. Public health and individual efforts are needed to improve the adoption and maintenance of healthy lifestyles in young adults.

Blinded by the light: on the relationship between CO first overtone emission and mass accretion rate in massive young stellar objects

NASA Astrophysics Data System (ADS)

Ilee, J. D.; Oudmaijer, R. D.; Wheelwright, H. E.; Pomohaci, R.

2018-07-01

To date, there is no explanation as to why disc-tracing CO first overtone (or `bandhead') emission is not a ubiquitous feature in low- to medium-resolution spectra of massive young stellar objects (MYSOs), but instead is only detected towards approximately 25 per cent of their spectra. In this paper, we investigate the hypothesis that only certain mass accretion rates result in detectable bandhead emission in the near-infrared spectra of MYSOs. Using an analytic disc model combined with an LTE model of the CO emission, we find that high accretion rates (≳10-4 M⊙ yr-1) result in large dust sublimation radii, a larger contribution to the K-band continuum from hot dust at the dust sublimation radius, and therefore correspondingly lower CO emission with respect to the continuum. On the other hand, low accretion rates (≲10-6 M⊙ yr-1) result in smaller dust sublimation radii, a correspondingly smaller emitting area of CO, and thus also lower CO emission with respect to the continuum. In general, moderate accretion rates produce the most prominent, and therefore detectable, CO first overtone emission. We compare our findings to a recent near-infrared spectroscopic survey of MYSOs, finding results consistent with our hypothesis. We conclude that the detection rate of CO bandhead emission in the spectra of MYSOs could be the result of MYSOs exhibiting a range of mass accretion rates, perhaps due to the variable accretion suggested by recent multi-epoch observations of these objects.

Blinded by the light: on the relationship between CO first overtone emission and mass accretion rate in massive young stellar objects

NASA Astrophysics Data System (ADS)

Ilee, J. D.; Oudmaijer, R. D.; Wheelwright, H. E.; Pomohaci, R.

2018-04-01

To date, there is no explanation as to why disc-tracing CO first overtone (or `bandhead') emission is not a ubiquitous feature in low- to medium-resolution spectra of massive young stellar objects, but instead is only detected toward approximately 25 per cent of their spectra. In this paper, we investigate the hypothesis that only certain mass accretion rates result in detectable bandhead emission in the near infrared spectra of MYSOs. Using an analytic disc model combined with an LTE model of the CO emission, we find that high accretion rates (≳ 10-4 M⊙yr-1) result in large dust sublimation radii, a larger contribution to the K-band continuum from hot dust at the dust sublimation radius, and therefore correspondingly lower CO emission with respect to the continuum. On the other hand, low accretion rates (≲ 10-6 M⊙yr-1) result in smaller dust sublimation radii, a correspondingly smaller emitting area of CO, and thus also lower CO emission with respect to the continuum. In general, moderate accretion rates produce the most prominent, and therefore detectable, CO first overtone emission. We compare our findings to a recent near-infrared spectroscopic survey of MYSOs, finding results consistent with our hypothesis. We conclude that the detection rate of CO bandhead emission in the spectra of MYSOs could be the result of MYSOs exhibiting a range of mass accretion rates, perhaps due to the variable accretion suggested by recent multi-epoch observations of these objects.

Outflow activities in the young high-mass stellar object G23.44-0.18

NASA Astrophysics Data System (ADS)

Ren, Jeremy Zhiyuan; Liu, Tie; Wu, Yuefang; Li, Lixin

2011-07-01

We present an observational study towards the young high-mass star-forming region G23.44-0.18 using the Submillimeter Array. Two massive, radio-quiet dusty cores MM1 and MM2 are observed in 1.3-mm continuum emission and dense molecular gas tracers including thermal CH3OH, CH3CN, HNCO, SO, and OCS lines. The 12CO (2-1) line reveals a strong bipolar outflow originating from MM2. The outflow consists of a low-velocity component with wide-angle quasi-parabolic shape and a more compact and collimated high-velocity component. The overall geometry resembles the outflow system observed in the low-mass protostar which has a jet-driven fast flow and entrained gas shell. The outflow has a dynamical age of 6 × 103 yr and a mass loss rate ˜10-3 M ⊙ yr-1. A prominent shock emission in the outflow is observed in SO and OCS, and also detected in CH3OH and HNCO. We investigated the chemistry of MM1, MM2 and the shocked region. The dense core MM2 have molecular abundances of three to four times higher than those in MM1. The abundance excess, we suggest, can be a net effect of the stellar evolution and embedded shocks in MM2 that calls for further inspection.

Fundamental Parameters Of The Lowest Mass Stars To The Highest Mass Planets

NASA Astrophysics Data System (ADS)

Filippazzo, Joseph C.

2016-09-01

The physical and atmospheric properties of ultracool dwarfs are deeply entangled due to the degenerate effects of mass, age, metallicity, clouds and dust, activity, rotation, and possibly even formation mechanism on observed spectra. Accurate determination of funda- mental parameters for a wide diversity of objects at the low end of the initial mass function (IMF) is thus crucial to testing stellar and planetary formation theories. To determine these quantities, we constructed and flux calibrated nearly-complete spectral energy distributions (SEDs) for 234 M, L, T, and Y dwarfs using published parallaxes and (0.3-40 \\mu m) spectra and photometry. From these homogeneous SEDs, we calculated bolometric luminosity ((L_\\text{bol})), effective temperature ((T_\\text{off})), mass, surface gravity, radius, spectral indexes, synthetic photometry, and bolometric corrections (BCs) for each object. We used these results to derive (L_\\text{bol}), (T_\\text{eff}), and BC polynomial relations across the entire very-low-mass star/brown dwarf/planetary mass regime. We use a subsample of objects with age constraints based on nearby young moving group membership, companionship with a young star, or spectral signatures of low surface gravity to define new age-sensitive diagnostics and characterize the reddening of young substellar atmospheres as a redistribution of flux from the near-infrared (NIR) into the mid-infrared (MIR). Consequently we find the SED flux pivots at K-band, making BCK as a function of spectral type a reliable, age-independent relationship. We find that young L dwarfs are systematically 300 K cooler than field age objects of the same spectral type and up to 600 K cooler than field age objects of the same absolute H magnitude. These findings are used to create prescriptions for the reliable and efficient characterization of new ultracool dwarfs using heterogeneous and limited spectral data.

Study of a variable mass Atwood's machine using a smartphone

NASA Astrophysics Data System (ADS)

Lopez, Dany; Caprile, Isidora; Corvacho, Fernando; Reyes, Orfa

2018-03-01

The Atwood machine was invented in 1784 by George Atwood and this system has been widely studied both theoretically and experimentally over the years. Nowadays, it is commonplace that many experimental physics courses include both Atwood's machine and variable mass to introduce more complex concepts in physics. To study the dynamics of the masses that compose the variable Atwood's machine, laboratories typically use a smart pulley. Now, the first work that introduced a smartphone as data acquisition equipment to study the acceleration in the Atwood's machine was the one by M. Monteiro et al. Since then, there has been no further information available on the usage of smartphones in variable mass systems. This prompted us to do a study of this kind of system by means of data obtained with a smartphone and to show the practicality of using smartphones in complex experimental situations.

The Frequency of Low-Mass Exoplanets

NASA Astrophysics Data System (ADS)

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

2009-08-01

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 α ~ -1 (for dN/dM vprop M α) and that between 15% ± 10% (at α = -0.3) and 48% ± 34% (at α = -1.3) of stars host planets with orbital periods of less than 16 days and minimum masses greater than 3 M ⊕.

Effects of a low-glycemic load vs low-fat diet in obese young adults: a randomized trial.

PubMed

Ebbeling, Cara B; Leidig, Michael M; Feldman, Henry A; Lovesky, Margaret M; Ludwig, David S

2007-05-16

The results of clinical trials involving diet in the treatment of obesity have been inconsistent, possibly due to inherent physiological differences among study participants. To determine whether insulin secretion affects weight loss with 2 popular diets. Randomized trial of obese young adults (aged 18-35 years; n = 73) conducted from September 2004 to December 2006 in Boston, Mass, and consisting of a 6-month intensive intervention period and a 12-month follow-up period. Serum insulin concentration at 30 minutes after a 75-g dose of oral glucose was determined at baseline as a measure of insulin secretion. Outcomes were assessed at 6, 12, and 18 months. Missing data were imputed conservatively. A low-glycemic load (40% carbohydrate and 35% fat) vs low-fat (55% carbohydrate and 20% fat) diet. Body weight, body fat percentage determined by dual-energy x-ray absorptiometry, and cardiovascular disease risk factors. Change in body weight and body fat percentage did not differ between the diet groups overall. However, insulin concentration at 30 minutes after a dose of oral glucose was an effect modifier (group x time x insulin concentration at 30 minutes: P = .02 for body weight and P = .01 for body fat percentage). For those with insulin concentration at 30 minutes above the median (57.5 microIU/mL; n = 28), the low-glycemic load diet produced a greater decrease in weight (-5.8 vs -1.2 kg; P = .004) and body fat percentage (-2.6% vs -0.9%; P = .03) than the low-fat diet at 18 months. There were no significant differences in these end points between diet groups for those with insulin concentration at 30 minutes below the median level (n = 28). Insulin concentration at 30 minutes after a dose of oral glucose was not a significant effect modifier for cardiovascular disease risk factors. In the full cohort, plasma high-density lipoprotein cholesterol and triglyceride concentrations improved more on the low-glycemic load diet, whereas low-density lipoprotein cholesterol

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

Intermediate to low-mass stellar content of Westerlund 1

NASA Astrophysics Data System (ADS)

Brandner, W.; Clark, J. S.; Stolte, A.; Waters, R.; Negueruela, I.; Goodwin, S. P.

2008-01-01

We have analysed near-infrared NTT/SofI observations of the starburst cluster Westerlund 1, which is among the most massive young clusters in the Milky Way. A comparison of colour-magnitude diagrams with theoretical main-sequence and pre-main sequence evolutionary tracks yields improved extinction and distance estimates of AKs = 1.13 ± 0.03 mag and d = 3.55 ± 0.17 kpc (DM = 12.75 ± 0.10 mag). The pre-main sequence population is best fit by a Palla & Stahler isochrone for an age of 3.2 Myr, while the main sequence population is in agreement with a cluster age of 3 to 5 Myr. An analysis of the structural parameters of the cluster yields that the half-mass radius of the cluster population increases towards lower mass, indicative of the presence of mass segregation. The cluster is clearly elongated with an eccentricity of 0.20 for stars with masses between 10 and 32 M_⊙, and 0.15 for stars with masses in the range 3 to 10 M_⊙. We derive the slope of the stellar mass function for stars with masses between 3.4 and 27 M_⊙. In an annulus with radii between 0.75 and 1.5 pc from the cluster centre, we obtain a slope of Γ = -1.3. Closer in, the mass function of Westerlund 1 is shallower with Γ = -0.6. The extrapolation of the mass function for stars with masses from 0.08 to 120 M_⊙ yields an initial total stellar mass of ≈52 000 M_⊙, and a present-day mass of 20 000 to 45 000 M_⊙ (about 10 times the stellar mass of the Orion nebula cluster, and 2 to 4 times the mass of the NGC 3603 young cluster), indicating that Westerlund 1 is the most massive starburst cluster identified to date in the Milky Way. Based on observations collected at the European Southern Observatory, La Silla, Chile, and retrieved from the ESO archive (Prog ID 67.C-0514).

Relation of Low Body Mass Index to Low Urinary Creatinine Excretion Rate in Patients with Coronary Heart Disease

PubMed Central

Bansal, Nisha; Hsu, Chi-yuan; Zhao, Shoujun; Whooley, Mary A.; Ix, Joachim H.

2011-01-01

In patients with prevalent coronary heart disease (CHD), studies have found a paradoxical relationship in that patients with higher body mass index (BMI) have lower mortality. One possibility is that individuals with higher BMI have greater muscle mass; and higher BMI may be a marker of better overall health status. We evaluated whether the paradoxical association of BMI with mortality in CHD patients is attenuated when accounting for urinary creatinine excretion, a marker of muscle mass. The Heart and Soul Study is an observational study of outpatients with stable CHD designed to investigate the influence of psychosocial factors on the progression of CHD. Outpatient 24-hour timed urine collections were obtained. Participants were followed up for death for 5.9 (± 1.9) years. Cox proportional hazards models evaluate the association between sex-specific BMI quintiles and mortality. There were 886 participants in our study population. Participants in higher quintiles of BMI were younger, more likely to have diabetes mellitus and hypertension and had higher urinary creatinine excretion rate. Compared to the lowest BMI quintile, subjects in higher BMI quintiles were less likely to die during follow-up. Adjustment for major demographic variables, traditional cardiovascular risk factors and kidney function did not attenuate the relationship. Additional adjustment for urinary creatinine excretion rate did not materially change the association between BMI and all-cause mortality. In conclusion, low muscle mass and low BMI are each associated with greater all-cause mortality, however low muscle mass does not appear to explain why CHD patients with low BMI have worse survival. PMID:21529727

VLA Ammonia Observations of IRAS 16253-2429: A Very Young and Low Mass Protostellar System

NASA Technical Reports Server (NTRS)

Wiseman, Jennifer J.

2011-01-01

IRAS l6253-2429. 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. 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 as possibly one of the youngest and lowest mass sources in formation yet known.

Low-Frequency Temporal Variability in Mira and Semiregular Variables

NASA Astrophysics Data System (ADS)

Templeton, Matthew R.; Karovska, M.; Waagen, E. O.

2012-01-01

We investigate low-frequency variability in a large sample of Mira and semiregular variables with long-term visual light curves from the AAVSO International Database. Our aim is to determine whether we can detect and measure long-timescale variable phenomena in these stars, for example photometric variations that might be associated with supergranular convection. We analyzed the long-term light curves of 522 variable stars of the Mira and SRa, b, c, and d classes. We calculated their low-frequency time-series spectra to characterize rednoise with the power density spectrum index, and then correlate this index with other observable characteristics such as spectral type and primary pulsation period. In our initial analysis of the sample, we see that the semiregular variables have a much broader range of spectral index than the Mira types, with the SRb subtype having the broadest range. Among Mira variables we see that the M- and S-type Miras have similarly wide ranges of index, while the C-types have the narrowest with generally shallower slopes. There is also a trend of steeper slope with larger amplitude, but at a given amplitude, a wide range of slopes are seen. The ultimate goal of the project is to identify stars with strong intrinsic red noise components as possible targets for resolved surface imaging with interferometry.

2MASS J13243553+6358281 Is an Early T-type Planetary-mass Object in the AB Doradus Moving Group

NASA Astrophysics Data System (ADS)

Gagné, Jonathan; Allers, Katelyn N.; Theissen, Christopher A.; Faherty, Jacqueline K.; Bardalez Gagliuffi, Daniella; Artigau, Étienne

2018-02-01

We present new radial velocity and trigonometric distance measurements indicating that the unusually red and photometrically variable T2 dwarf 2MASS J13243553+6358281 is a member of the young (∼150 Myr) AB Doradus moving group (ABDMG) based on its space velocity. We estimate its model-dependent mass in the range 11–12 M Jup at the age of the ABDMG, and its trigonometric distance of 12.7 ± 1.5 pc makes it one of the nearest known isolated planetary-mass objects. The unusually red continuum of 2MASS J13243553+6358281 in the near-infrared was previously suspected to be caused by an unresolved L + T brown dwarf binary, although it was never observed with high spatial resolution imaging. This new evidence of youth suggests that a low surface gravity may be sufficient to explain this peculiar feature. Using the new parallax we find that its absolute J-band magnitude is ∼0.4 mag fainter than equivalent-type field brown dwarfs, suggesting that the binary hypothesis is unlikely. The fundamental properties of 2MASS J13243553+6358281 follow the spectral type sequence of other known high-likelihood members of the ABDMG. The effective temperature of 2MASS J13243553+6358281 provides the first precise constraint on the L/T transition at a known young age and indicates that it happens at a temperature of ∼1150 K at ∼150 Myr, compared to ∼1250 K for field brown dwarfs.

YSOVAR: MID-INFRARED VARIABILITY OF YOUNG STELLAR OBJECTS AND THEIR DISKS IN THE CLUSTER IRAS 20050+2720

DOE Office of Scientific and Technical Information (OSTI.GOV)

Poppenhaeger, K.; Wolk, S. J.; Hora, J. L.

2015-10-15

We present a time-variability study of young stellar objects (YSOs) in the cluster IRAS 20050+2720, performed at 3.6 and 4.5 μm with the Spitzer Space Telescope; this study is part of the Young Stellar Object VARiability (YSOVAR) project. We have collected light curves for 181 cluster members over 60 days. We find a high variability fraction among embedded cluster members of ca. 70%, whereas young stars without a detectable disk display variability less often (in ca. 50% of the cases) and with lower amplitudes. We detect periodic variability for 33 sources with periods primarily in the range of 2–6 days.more » Practically all embedded periodic sources display additional variability on top of their periodicity. Furthermore, we analyze the slopes of the tracks that our sources span in the color–magnitude diagram (CMD). We find that sources with long variability time scales tend to display CMD slopes that are at least partially influenced by accretion processes, while sources with short variability timescales tend to display extinction-dominated slopes. We find a tentative trend of X-ray detected cluster members to vary on longer timescales than the X-ray undetected members.« less

The effectiveness of mass media in changing HIV/AIDS-related behaviour among young people in developing countries.

PubMed

Bertrand, Jane T; Anhang, Rebecca

2006-01-01

To review the strength of the evidence for the effects of three types of mass media interventions (radio only, radio with supporting media, or radio and television with supporting media) on HIV/AIDS-related behaviour among young people in developing countries and to assess whether these interventions reach the threshold of evidence needed to recommend widespread implementation. We conducted a systematic review of studies that evaluated mass media interventions and were published or released between 1990 and 2004. Studies were included if they evaluated a mass media campaign that had the main objective of providing information about HIV/AIDS or sexual health. To be eligible for inclusion studies had to use a pre-intervention versus post-intervention design or an intervention versus control design or analyse cross-sectional data comparing those who had been exposed to the campaign with those who had not been exposed. Studies also had to comprehensively report quantitative data for most outcomes. Of the 15 programmes identified, 11 were from Africa, 2 from Latin America, 1 from Asia, and 1 from multiple countries. One programme used radio only, six used radio with supporting media, and eight others used television and radio with supporting media. The data support the effectiveness of mass media interventions to increase the knowledge of HIV transmission, to improve self-efficacy in condom use, to influence some social norms, to increase the amount of interpersonal communication, to increase condom use and to boost awareness of health providers. Fewer significant effects were found for improving self-efficacy in terms of abstinence, delaying the age of first sexual experience or decreasing the number of sexual partners. We found that mass media programmes can influence HIV-related outcomes among young people, although not on every variable or in every campaign. Campaigns that include television require the highest threshold of evidence, yet they also yield the

Kinematics of a Young Low-mass Star-forming Core: Understanding the Evolutionary State of the First-core Candidate L1451-mm

NASA Astrophysics Data System (ADS)

Maureira, María José; Arce, Héctor G.; Dunham, Michael M.; Pineda, Jaime E.; Fernández-López, Manuel; Chen, Xuepeng; Mardones, Diego

2017-03-01

We use 3 mm multiline and continuum CARMA observations toward the first hydrostatic core (FHSC) candidate L1451-mm to characterize the envelope kinematics at 1000 au scales and investigate its evolutionary state. We detect evidence of infall and rotation in the NH2D(11,1-10,1), N2H+(1-0), and HCN(1-0) molecular lines. We compare the position-velocity diagram of the NH2D(11,1-10,1) line with a simple kinematic model and find that it is consistent with an envelope that is both infalling and rotating while conserving angular momentum around a central mass of about 0.06 M ⊙. The N2H+(1-0) LTE mass of the envelope along with the inferred infall velocity leads to a mass infall rate of approximately 6 × 10-6 M ⊙ yr-1, implying a young age of 104 years for this FHSC candidate. Assuming that the accretion onto the central object is the same as the infall rate, we obtain a minimum source size of 1.5-5 au, consistent with the size expected for a first core. We do not see any evidence of outflow motions or signs of outflow-envelope interaction at scales ≳2000 au. This is consistent with previous observations that revealed a very compact outflow (≲500 au). We conclude that L1451-mm is indeed at a very early stage of evolution, either a first core or an extremely young Class 0 protostar. Our results provide strong evidence that L1451-mm is the best candidate for being a bona fide first core.

Planets around Low-mass Stars (PALMS). VI. Discovery of a Remarkably Red Planetary-mass Companion to the AB Dor Moving Group Candidate 2MASS J22362452+4751425*

NASA Astrophysics Data System (ADS)

Bowler, Brendan P.; Liu, Michael C.; Mawet, Dimitri; Ngo, Henry; Malo, Lison; Mace, Gregory N.; McLane, Jacob N.; Lu, Jessica R.; Tristan, Isaiah I.; Hinkley, Sasha; Hillenbrand, Lynne A.; Shkolnik, Evgenya L.; Benneke, Björn; Best, William M. J.

2017-01-01

We report the discovery of an extremely red planetary-mass companion to 2MASS J22362452+4751425, a ≈0.6 M⊙ late-K dwarf likely belonging to the ˜120 Myr AB Doradus moving group. 2M2236+4751 b was identified in multi-epoch NIRC2 adaptive optics imaging at Keck Observatory at a separation of 3\\buildrel{\\prime\\prime}\\over{.} 7, or 230 ± 20 AU in projection at the kinematic distance of 63 ± 5 pc to its host star. Assuming membership in the AB Dor group, as suggested from its kinematics, the inferred mass of 2M2236+4751 b is 11-14 MJup. Follow-up Keck/OSIRIS K-band spectroscopy of the companion reveals strong CO absorption similar to other faint red L dwarfs and lacks signs of methane absorption, despite having an effective temperature of ≈900-1200 K. With a (J-K)MKO color of 2.69 ± 0.12 mag, the near-infrared slope of 2M2236+4751 b is redder than all of the HR 8799 planets and instead resembles the ≈23 Myr isolated planetary-mass object PSO J318.5-22, implying that similarly thick photospheric clouds can persist in the atmospheres of giant planets at ages beyond 100 Myr. In near-infrared color-magnitude diagrams, 2M2236+4751 b is located at the tip of the red L dwarf sequence and appears to define the “elbow” of the AB Dor substellar isochrone separating low-gravity L dwarfs from the cooler young T dwarf track. 2M2236+4751 b is the reddest substellar companion to a star and will be a valuable benchmark to study the shared atmospheric properties of young low-mass brown dwarfs and extrasolar giant planets. Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation.

Bipolar Molecular Outflows within 1pc of Sgr A*:Evidence for Low-mass Star Formation Activity

NASA Astrophysics Data System (ADS)

Yusef-Zadeh, Farhad; Wardle, Mark; Kunneriath, Devaky; Royster, Marc; Wootten, Al; Roberts, Douglas

2018-01-01

The 4 million solar mass black hole, Sgr A*, is expected to suppress star formation because the measured density of the cloud is insufficient for self-gravity to overcome tidal disruption by the black hole's gravitational field. Nevertheless, objects resembling dust-enshrouded young stars and photo-evaporative flows from their disks have been identified within 2pc of Sgr A*. Clear identification of the nature of these objects has been hampered by the Galactic center's distance, 30 magnitudes of foreground extinction, and stellar crowding. Here, we report the discovery of 11 bipolar molecular outflows using ALMA within a projected distance of one pc from Sgr A*. These unambiguous signatures of young protostars manifest as approaching and receding lobes of dense gas swept up by the jets created during the formation and early evolution of low-mass stars. The mean dynamical age of the outflow sources and the rate of star formation are estimated to be ~6500 years and ~5x10^{-4} solar mass per year, respectively. These measurements suggest that star formation could take place in the immediate vicinity of supermassive black holes in the nuclei of external galaxies.

EVIDENCE FOR CLUSTER TO CLUSTER VARIATIONS IN LOW-MASS STELLAR ROTATIONAL EVOLUTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coker, Carl T.; Pinsonneault, Marc; Terndrup, Donald M., E-mail: coker@astronomy.ohio-state.edu, E-mail: pinsono@astronomy.ohio-state.edu, E-mail: terndrup@astronomy.ohio-state.edu

2016-12-10

The concordance model for angular momentum evolution postulates that star-forming regions and clusters are an evolutionary sequence that can be modeled with assumptions about protostar–disk coupling, angular momentum loss from magnetized winds that saturates in a mass-dependent fashion at high rotation rates, and core-envelope decoupling for solar analogs. We test this approach by combining established data with the large h Per data set from the MONITOR project and new low-mass Pleiades data. We confirm prior results that young low-mass stars can be used to test star–disk coupling and angular momentum loss independent of the treatment of internal angular momentum transport.more » For slow rotators, we confirm the need for star–disk interactions to evolve the ONC to older systems, using h Per (age 13 Myr) as our natural post-disk case. There is no evidence for extremely long-lived disks as an alternative to core-envelope decoupling. However, our wind models cannot evolve rapid rotators from h Per to older systems consistently, and we find that this result is robust with respect to the choice of angular momentum loss prescription. We outline two possible solutions: either there is cosmic variance in the distribution of stellar rotation rates in different clusters or there are substantially enhanced torques in low-mass rapid rotators. We favor the former explanation and discuss observational tests that could be used to distinguish them. If the distribution of initial conditions depends on environment, models that test parameters by assuming a universal underlying distribution of initial conditions will need to be re-evaluated.« less

Light-curve Modulation of Low-mass Stars in K2. I. Identification of 481 Fast Rotators in the Solar Neighborhood

NASA Astrophysics Data System (ADS)

Saylor, Dicy; Lepine, Sebastien; Crossfield, Ian; Petigura, Erik A.

2018-01-01

The K2 mission is targeting large numbers of nearby (d < 100 pc) GKM dwarfs selected from the SUPERBLINK proper motion survey (μ > 40 mas yr‑1, V < 20). Additionally, the mission is targeting low-mass, high proper motion stars associated with the local (d < 500 pc) Galactic halo population also selected from SUPERBLINK. K2 campaigns 0 through 8 monitored a total of 26,518 of these cool main-sequence stars. We used the auto-correlation function to search for fast rotators by identifying short-period photometric modulations in the K2 light curves. We identified 481 candidate fast rotators with rotation periods <4 days that show light-curve modulations consistent with starspots. Their kinematics show low average transverse velocities, suggesting that they are part of the young disk population. A subset (13) of the fast rotators is found among those targets with colors and kinematics consistent with the local Galactic halo population and may represent stars spun up by tidal interactions in close binary systems. We further demonstrate that the M dwarf fast rotators selected from the K2 light curves are significantly more likely to have UV excess and discuss the potential of the K2 mission to identify new nearby young GKM dwarfs on the basis of their fast rotation rates. Finally, we discuss the possible use of local halo stars as fiducial, non-variable sources in the Kepler fields.

Doubling down on peptide phosphorylation as a variable mass modification

USDA-ARS?s Scientific Manuscript database

Some mass spectrometrists believe that searching for variable post-translational modifications like phosphorylation of serine or threonine when using database-search algorithms to interpret peptide tandem mass spectra will increase false positive rates. The basis for this is the premise that the al...

Cloudless Atmospheres for Young Low-Gravity Substellar Objects

NASA Technical Reports Server (NTRS)

Tremblin, P.; Chabrier, G.; Baraffe, I.; Liu, Michael C.; Magnier, E. A.; Lagage, P.-O.; De Oliveira, C. Alves; Burgasser, A. J.; Amundsen, D. S.; Drummond, B.

2017-01-01

Atmospheric modeling of low-gravity (VL-G) young brown dwarfs remains challenging. The presence of very thick clouds is a possible source of this challenge, because of their extremely red near-infrared (NIR) spectra, but no cloud models provide a good fit to the data with a radius compatible with the evolutionary models for these objects. We show that cloudless atmospheres assuming a temperature gradient reduction caused by fingering convection provide a very good model to match the observed VL-G NIR spectra. The sequence of extremely red colors in the NIR for atmospheres with effective temperatures from approx. 2000 K down to approx. 1200 K is very well reproduced with predicted radii typical of young low-gravity objects. Future observations with NIRSPEC and MIRI on the James Webb Space Telescope (JWST) will provide more constraints in the mid-infrared, helping to confirm or refute whether or not the NIR reddening is caused by fingering convection. We suggest that the presence or absence of clouds will be directly determined by the silicate absorption features that can be observed with MIRI. JWST will therefore be able to better characterize the atmosphere of these hot young brown dwarfs and their low-gravity exoplanet analogs.

A generation at risk: a cross-sectional study on HIV/AIDS knowledge, exposure to mass media, and stigmatizing behaviors among young women aged 15-24 years in Ghana.

PubMed

Asamoah, Charity Konadu; Asamoah, Benedict Oppong; Agardh, Anette

2017-01-01

HIV/AIDS stigmatizing behaviors are a huge barrier to early detection and treatment of individuals with the AIDS virus. HIV/AIDS stigma and related consequences are debilitating, especially for vulnerable populations. This study sought to assess whether young women's HIV/AIDS knowledge levels and exposure to mass media (television and radio) have an influence on their stigmatizing behaviors and role as agents of stigma towards individuals living with HIV and AIDS. The data used for this study originated from the Ghana Multiple Indicator Cluster Survey 2011. Binary and multiple (stepwise) logistic regression analyses were used to examine the associations between HIV/AIDS knowledge, frequency of exposure to mass media, and HIV/AIDS stigmatizing behaviors among young women aged 15-24 years in Ghana. Of the 3573 young women, 80% of 15-19-year-olds and 76% of 20-24-year-olds had at least one stigmatizing behavior towards persons living with HIV/AIDS (PLHA). Young women with increased knowledge regarding HIV/AIDS and frequent exposure to mass media (television and radio) had lesser tendency to stigmatize or act as agents of stigma towards PLHA (proportion with at least one stigmatizing behavior per subgroup - HIV/AIDS knowledge: those with highest knowledge score 579 [70.1%], those with lowest knowledge score 28 [90.3%]; mass media: those with daily exposure 562 [73.4%], those not exposed at all 249 [89.2%]). There was a graded negative 'exposure-response' association between the ranked variables: HIV/AIDS knowledge, mass media, and HIV/AIDS stigmatizing behaviors. The significant inverse association between HIV/AIDS knowledge, frequency of exposure to mass media, and HIV/AIDS stigmatizing behaviors persisted even after adjusting for all other covariates in the multiple logistic regression models. It is extremely important to increase HIV/AIDS-related knowledge and reduce stigma among young women in Ghana through targeted HIV/AIDS factual knowledge transfer. The

The dynamical mass of a classical Cepheid variable star in an eclipsing binary system.

PubMed

Pietrzyński, G; Thompson, I B; Gieren, W; Graczyk, D; Bono, G; Udalski, A; Soszyński, I; Minniti, D; Pilecki, B

2010-11-25

Stellar pulsation theory provides a means of determining the masses of pulsating classical Cepheid supergiants-it is the pulsation that causes their luminosity to vary. Such pulsational masses are found to be smaller than the masses derived from stellar evolution theory: this is the Cepheid mass discrepancy problem, for which a solution is missing. An independent, accurate dynamical mass determination for a classical Cepheid variable star (as opposed to type-II Cepheids, low-mass stars with a very different evolutionary history) in a binary system is needed in order to determine which is correct. The accuracy of previous efforts to establish a dynamical Cepheid mass from Galactic single-lined non-eclipsing binaries was typically about 15-30% (refs 6, 7), which is not good enough to resolve the mass discrepancy problem. In spite of many observational efforts, no firm detection of a classical Cepheid in an eclipsing double-lined binary has hitherto been reported. Here we report the discovery of a classical Cepheid in a well detached, double-lined eclipsing binary in the Large Magellanic Cloud. We determine the mass to a precision of 1% and show that it agrees with its pulsation mass, providing strong evidence that pulsation theory correctly and precisely predicts the masses of classical Cepheids.

3B.02: 24-HOUR AMBULATORY CENTRAL BLOOD PRESSURE VARIABILITY AND TARGET-ORGAN DAMAGE IN ADOLESCENTS AND YOUNG ADULTS.

PubMed

Ntineri, A; Kollias, A; Zeniodi, M; Moyssakis, I; Georgakopoulos, D; Servos, G; Vazeou, A; Stergiou, G S

2015-06-01

Some studies suggested that ambulatory blood pressure (ABP) variability may provide useful information beyond that of average ABP levels. This study investigated the relationship between central ABP variability and target-organ damage in young individuals in whom the central-peripheral blood pressure discrepancy might be considerable. Apparently healthy adolescents and young adults referred for elevated blood pressure and healthy volunteers (age 12-26 years) were subjected to: (i) 24-hour monitoring of central ABP using a noninvasive brachial cuff-based oscillometric device (Mobil-O-Graph 24 h PWA); (ii) 24-hour pulse wave velocity (PWV) monitoring (Mobil-O-Graph 24 h PWA); (iii) echocardiographic determination of left ventricular mass index (LVMI); (iv) measurement (ultrasonography) of the common carotid intima-media thickness (IMT). The standard deviation (SD) of ABP (24-hour weighted/awake/asleep), as well as the respective coefficients of variation (CV) were used for assessing variability. The study included 68 individuals (mean age 18.7 ± 4.7 years, 52 males, body mass index [BMI] 24.5 ± 4.7 kg/m, 24 volunteers, 15 with hypertension [24-hour peripheral ABP >=95th percentile for adolescents or >=130/80 mmHg for adults]). LVMI was correlated with 24-hour/awake/asleep central systolic ABP (r=0.50/0.49/0.40, all p < 0.01), as well as with 24-hour weighted/awake/asleep SD of central systolic ABP (r = 0.40/0.37/0.30, all p < 0.05), whereas no association was observed for the respective CV. IMT was correlated with 24-hour/awake/asleep central pulse pressure (PP) (r = 0.37/0.33/0.27, all p < 0.05), 24-hour weighted/awake/asleep SD of central PP (r = 0.43/0.40/0.36, all p < 0.01) and the respective CV (r = 0.28/0.26/0.25, all p < 0.05). Regarding 24-hour PWV, there was a significant association with 24-hour/awake/asleep central systolic ABP (r = 0.94/0.88/0.84, all p < 0.001) and 24-hour weighted

Spitzer IRS Observations of Low-Mass Seyfert Galaxies

NASA Astrophysics Data System (ADS)

Thornton, Carol E.; Barth, Aaron J.; Ho, Luis C.; Greene, Jenny E.

2010-05-01

The Sloan Digital Sky Survey has made it possible to identify the first samples of active galaxies with estimated black hole masses below ~ 106 M⊙. We have obtained Spitzer IRS low-resolution spectra, covering 5-38 μm, of a sample of 41 Seyfert galaxies with low-mass black holes. Our sample includes SDSS-selected objects from the low-mass Seyfert 1 sample of Greene & Ho (2004) and the low-mass Seyfert 2 sample of Barth et al. (2008), as well as NGC 4395 and POX 52. The goals of this work are to examine the dust emission properties of these objects and investigate the relationship between type 1 and type 2 AGNs at low luminosities and low masses, to search for evidence of star formation, and to use emission-line diagnostics to constrain physical conditions within the narrow-line regions. Here we present preliminary results from this project.

Spitzer IRS Observations of Low-Mass Seyfert Galaxies

NASA Astrophysics Data System (ADS)

Thornton, Carol E.; Barth, A. J.; Greene, J. E.; Ho, L. C.

2009-05-01

The Sloan Digital Sky Survey has made it possible to identify the first samples of active galaxies with estimated black hole masses below 106 solar masses. We have obtained Spitzer IRS low-resolution spectra, covering 5-30 microns, of a sample of 41 Seyfert galaxies with low-mass black holes. Our sample includes SDSS-selected objects from the low-mass Seyfert 1 sample of Greene & Ho (2004) and the low-mass Seyfert 2 sample of Barth et al. (2008), as well as NGC 4395 and POX 52. The goals of this work are to examine the dust emission properties of these objects and investigate the relationship between Type 1 and Type 2 AGNs at low luminosities and low masses, to search for evidence of star formation, and to use emission-line diagnostics to constrain physical conditions within the narrow-line regions. We will present preliminary results from this project, including measurements of continuum shapes and dust temperatures, narrow-line region diagnostics, and PAH features, derived using the IDL code PAHFIT (Smith et al. 2007).

Bone mineral density in relation to body mass index among young women: a prospective cohort study.

PubMed

Elgán, Carina; Fridlund, Bengt

2006-08-01

To identify important predictors among lifestyle behaviours and physiological factors of bone mineral density (BMD) in relation to body mass index (BMI) among young women over a 2-year period. DESIGN, SAMPLE AND MEASUREMENTS: Data were collected in 1999 and 2001. Healthy young women (n=152) completed a questionnaire. BMD measurements were performed by DEXA in the calcaneus. The women were subdivided into three categories according to baseline BMI. Baseline bodyweight explained 25% of the variability in BMD at follow-up in the BMI<19 category, and high physical activity seemed to hinder BMD development. In the BMI>24 category, a difference in time spent outdoors during winter between baseline and follow-up was the single most important factor for BMD levels. Overweight women with periods of amenorrhoea had lower BMD than overweight women without such periods. Predictors and lifestyle behaviours associated with BMD are likely to be based on women of normal weight. BMI should be considered when advising on physical activity, since high physical activity seems to impair BMD development among underweight young women, possibly due to energy imbalance. Among overweight women, sleep satisfaction is the greatest predictor associated with BMD change and may indicate better bone formation conditions. Energy balance and sleep quality may be prerequisites of bone health and should be considered in prevention.

Leisure time physical activity of young women from the Carpathian Euroregion in relation to the Body Mass Index.

PubMed

Zadarko, Emilian; Barabasz, Zbigniew; Nizioł-Babiarz, Edyta; Zadarko Domaradzka, Maraia; Barabasz, Monika; Sobolewski, Marek; Palanska, Andrea; Bergier, Józef; Junger, Jan

2014-01-01

Carpathian Euroregion gathers the population of 5 countries, including Poland, Slovakia, Hungary and Romania- the European Union members, as well as Ukraine. Young women are statistically less involved in high-intensity physical activity than young men. The objective of this work was to assess the relation between physical activity of young women aged 18-21 years old and BMI and conditioning factors. The study was conducted between 2010 and 2011 among 2339 women. The Minnesota Leisure Time Physical Activity Questionnarie (MLTPAQ) was applied. It results from the study that 74,2% of young women is considered to have the proper BMI rate (18,5-24,9). As many as 16,2% is considered underweight and almost 10% have higher BMI rate and are overweight. More than one third of respondents did not gain the level of physical activity of 1000 kcal/week, and that is the minimum recommended amount of leisure physical activity time per week. In case of women with low level of physical activity (<1000 kcal), as many as 52% of week activity considered low-intensity activity EEPAlight. The character of changes of the BMI index with reference to the level of physical activity is very similar in the women from towns/cities and the women from villages. An increase of BMI along with the total physical activity was related among all to the increase of free fat mass FFM despite of the level of physical.

Kinematics of a Young Low-mass Star-forming Core: Understanding the Evolutionary State of the First-core Candidate L1451-mm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maureira, María José; Arce, Héctor G.; Dunham, Michael M.

We use 3 mm multiline and continuum CARMA observations toward the first hydrostatic core (FHSC) candidate L1451-mm to characterize the envelope kinematics at 1000 au scales and investigate its evolutionary state. We detect evidence of infall and rotation in the NH{sub 2}D(1{sub 1,1}–1{sub 0,1}), N{sub 2}H{sup +}(1–0), and HCN(1–0) molecular lines. We compare the position–velocity diagram of the NH{sub 2}D(1{sub 1,1}–1{sub 0,1}) line with a simple kinematic model and find that it is consistent with an envelope that is both infalling and rotating while conserving angular momentum around a central mass of about 0.06 M {sub ⊙}. The N{sub 2}H{supmore » +}(1–0) LTE mass of the envelope along with the inferred infall velocity leads to a mass infall rate of approximately 6 × 10{sup −6} M {sub ⊙} yr{sup −1}, implying a young age of 10{sup 4} years for this FHSC candidate. Assuming that the accretion onto the central object is the same as the infall rate, we obtain a minimum source size of 1.5–5 au, consistent with the size expected for a first core. We do not see any evidence of outflow motions or signs of outflow–envelope interaction at scales ≳2000 au. This is consistent with previous observations that revealed a very compact outflow (≲500 au). We conclude that L1451-mm is indeed at a very early stage of evolution, either a first core or an extremely young Class 0 protostar. Our results provide strong evidence that L1451-mm is the best candidate for being a bona fide first core.« less

Water in star-forming regions with Herschel (WISH). VI. Constraints on UV and X-ray irradiation from a survey of hydrides in low- to high-mass young stellar objects

NASA Astrophysics Data System (ADS)

Benz, A. O.; Bruderer, S.; van Dishoeck, E. F.; Melchior, M.; Wampfler, S. F.; van der Tak, F.; Goicoechea, J. R.; Indriolo, N.; Kristensen, L. E.; Lis, D. C.; Mottram, J. C.; Bergin, E. A.; Caselli, P.; Herpin, F.; Hogerheijde, M. R.; Johnstone, D.; Liseau, R.; Nisini, B.; Tafalla, M.; Visser, R.; Wyrowski, F.

2016-05-01

Context. Hydrides are simple compounds containing one or a few hydrogen atoms bonded to a heavier atom. They are fundamental precursor molecules in cosmic chemistry and many hydride ions have become observable in high quality for the first time thanks to the Herschel Space Observatory. Ionized hydrides such as CH+ and OH+ (and also HCO+), which affect the chemistry of molecules such as water, provide complementary information on irradiation by far-UV (FUV) or X-rays and gas temperature. Aims: We explore hydrides of the most abundant heavier elements in an observational survey covering young stellar objects (YSOs) with different mass and evolutionary state. The focus is on hydrides associated with the dense protostellar envelope and outflows, contrary to previous work that focused on hydrides in diffuse foreground clouds. Methods: Twelve YSOs were observed with HIFI on Herschel in six spectral settings providing fully velocity-resolved line profiles as part of the Water in star-forming regions with Herschel (WISH) program. The YSOs include objects of low (Class 0 and I), intermediate, and high mass, with luminosities ranging from 4 L⊙ to 2 × 105 L⊙. Results: The targeted lines of CH+, OH+, H2O+, C+, and CH are detected mostly in blue-shifted absorption. H3O+ and SH+ are detected in emission and only toward some high-mass objects. The observed line parameters and correlations suggest two different origins related to gas entrained by the outflows and to the circumstellar envelope. The derived column densities correlate with bolometric luminosity and envelope mass for all molecules, best for CH, CH+, and HCO+. The column density ratios of CH+/OH+ are estimated from chemical slab models, assuming that the H2 density is given by the specific density model of each object at the beam radius. For the low-mass YSOs the observed ratio can be reproduced for an FUV flux of 2-400 times the interstellar radiation field (ISRF) at the location of the molecules. In two high-mass

A study about the photometric variability in the M42 region

NASA Astrophysics Data System (ADS)

Lima, G. H. R. A.; Vaz, L. P. R.; Reipurth, B.

2003-08-01

The M42 region in Orion is one of the most active regarding stellar formation in the neighborhood of the solar system. At a distance of 450pc, it gives us an excellent oportunity to study star formation processes. By studying 22 films of this region, covering an area of 5 by 5 degrees, taken in almost regular intervals through 2.5 years by ESO 1m Schimdt Telescope, in La Silla, Chile, we seek to discover variable stars among the young stars. These films were digitalized by the SuperCOSMOS (the most precise scientific scanner today) team, and each film were exposed for 30 minutes. Our knowledge about the variability of low-mass young variable stars were outdated, and were based on old photographic plates, which were studied by the so called blink comparators and Iris photometers. Now we developed a process to study these data and identify possible candidate stars to be constants or variables, and developed some softwares based on this process. We also used some softwares supplied by the SuperCosmos team to help our analysis of the dataset. After identifying the stars, which we, definitively, can consider variables, we will study more deeply these ones in hope to obtain more data about the formation process. We expect to detect thousands of new variables within our data as also the light curves for each star detected.

A comparison between handgrip strength, upper limb fat free mass by segmental bioelectrical impedance analysis (SBIA) and anthropometric measurements in young males

NASA Astrophysics Data System (ADS)

Gonzalez-Correa, C. H.; Caicedo-Eraso, J. C.; Varon-Serna, D. R.

2013-04-01

The mechanical function and size of a muscle may be closely linked. Handgrip strength (HGS) has been used as a predictor of functional performing. Anthropometric measurements have been made to estimate arm muscle area (AMA) and physical muscle mass volume of upper limb (ULMMV). Electrical volume estimation is possible by segmental BIA measurements of fat free mass (SBIA-FFM), mainly muscle-mass. Relationship among these variables is not well established. We aimed to determine if physical and electrical muscle mass estimations relate to each other and to what extent HGS is to be related to its size measured by both methods in normal or overweight young males. Regression analysis was used to determine association between these variables. Subjects showed a decreased HGS (65.5%), FFM, (85.5%) and AMA (74.5%). It was found an acceptable association between SBIA-FFM and AMA (r2 = 0.60) and poorer between physical and electrical volume (r2 = 0.55). However, a paired Student t-test and Bland and Altman plot showed that physical and electrical models were not interchangeable (pt<0.0001). HGS showed a very weak association with anthropometric (r2 = 0.07) and electrical (r2 = 0.192) ULMMV showing that muscle mass quantity does not mean muscle strength. Other factors influencing HGS like physical training or nutrition require more research.

A 1.3 mm SMA survey of 29 variable young stellar objects

NASA Astrophysics Data System (ADS)

Liu, Hauyu Baobab; Dunham, Michael M.; Pascucci, Ilaria; Bourke, Tyler L.; Hirano, Naomi; Longmore, Steven; Andrews, Sean; Carrasco-González, Carlos; Forbrich, Jan; Galván-Madrid, Roberto; Girart, Josep M.; Green, Joel D.; Juárez, Carmen; Kóspál, Ágnes; Manara, Carlo F.; Palau, Aina; Takami, Michihiro; Testi, Leonardo; Vorobyov, Eduard I.

2018-04-01

Context. Young stellar objects (YSOs) may undergo periods of active accretion (outbursts), during which the protostellar accretion rate is temporarily enhanced by a few orders of magnitude. Whether or not these accretion outburst YSOs possess similar dust and gas reservoirs to each other, and whether or not their dust and gas reservoirs are similar as quiescent YSOs, are issues yet to be clarified. Aims: The aim of this work is to characterize the millimeter thermal dust emission properties of a statistically significant sample of long and short duration accretion outburst YSOs (i.e., FUors and EXors) and the spectroscopically identified candidates of accretion outbursting YSOs (i.e., FUor-like objects). Methods: We have carried out extensive Submillimeter Array (SMA) observations mostly at 225 GHz (1.33 mm) and 272 GHz (1.10 mm), from 2008 to 2017. We covered accretion outburst YSOs located at <1 kpc distances from the solar system. Results: We analyze all the existing SMA data of such objects, both published and unpublished, in a coherent way to present a millimeter interferometric database of 29 objects. We obtained 21 detections at >3σ significance. Detected sources except for the two cases of V883 Ori and NGC 2071 MM3 were observed with 1″ angular resolution. Overall our observed targets show a systematically higher millimeter luminosity distribution than those of the M* > 0.3 M⊙ Class II YSOs in the nearby (≲400 pc) low-mass star-forming molecular clouds (e.g., Taurus, Lupus, Upp Scorpio, and Chameleon I). In addition, at 1 mm our observed confirmed binaries or triple-system sources are systematically fainter than the rest of the sources even though their 1 mm fluxes are broadly distributed. We may have detected 30-60% millimeter flux variability from V2494 Cyg and V2495 Cyg, from the observations separated by approximately one year.

Body mass index, perceived and actual physical competence: the relationship among young children.

PubMed

Spessato, B C; Gabbard, C; Robinson, L; Valentini, N C

2013-11-01

The purpose of this study was to examine the relationship between perceived physical competence (PPC), actual motor competence (MC) and body mass index (BMI) in young children. We assessed MC (Test of Gross Motor Development - 2nd Edition), PPC (Pictorial Scale of Perceived Competence and Social Acceptance) and BMI (CDC calculator) of 178 young children ages 4-7 years. The linear regression model for the overall sample showed that BMI was a better predictor of PPC than MC. Also, obese children had lower PPC, but showed no differences in MC compared with leaner peers. PPC of young obese children was lower than their leaner counterparts, yet their MC was similar. That outcome draws attention to the importance of promoting positive PPC in young children. © 2012 John Wiley & Sons Ltd.

A Search for Water Maser Emission from Brown Dwarfs and Low-luminosity Young Stellar Objects

NASA Astrophysics Data System (ADS)

Gómez, José F.; Palau, Aina; Uscanga, Lucero; Manjarrez, Guillermo; Barrado, David

2017-05-01

We present a survey for water maser emission toward a sample of 44 low-luminosity young objects, comprising (proto-)brown dwarfs, first hydrostatic cores (FHCs), and other young stellar objects (YSOs) with bolometric luminosities lower than 0.4 L ⊙. Water maser emission is a good tracer of energetic processes, such as mass-loss and/or accretion, and is a useful tool to study these processes with very high angular resolution. This type of emission has been confirmed in objects with L bol ≳ 1 L ⊙. Objects with lower luminosities also undergo mass-loss and accretion, and thus, are prospective sites of maser emission. Our sensitive single-dish observations provided a single detection when pointing toward the FHC L1448 IRS 2E. However, follow-up interferometric observations showed water maser emission associated with the nearby YSO L1448 IRS 2 (a Class 0 protostar of L bol ≃ 3.6-5.3 L ⊙) and did not find any emission toward L1448 IRS 2E. The upper limits for water maser emission determined by our observations are one order of magnitude lower than expected from the correlation between water maser luminosities and bolometric luminosities found for YSOs. This suggests that this correlation does not hold at the lower end of the (sub)stellar mass spectrum. Possible reasons are that the slope of this correlation is steeper at L bol ≤ 1 L ⊙ or that there is an absolute luminosity threshold below which water maser emission cannot be produced. Alternatively, if the correlation still stands at low luminosity, the detection rates of masers would be significantly lower than the values obtained in higher-luminosity Class 0 protostars.

A Search for Water Maser Emission from Brown Dwarfs and Low-luminosity Young Stellar Objects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gómez, José F.; Manjarrez, Guillermo; Palau, Aina

We present a survey for water maser emission toward a sample of 44 low-luminosity young objects, comprising (proto-)brown dwarfs, first hydrostatic cores (FHCs), and other young stellar objects (YSOs) with bolometric luminosities lower than 0.4 L {sub ⊙}. Water maser emission is a good tracer of energetic processes, such as mass-loss and/or accretion, and is a useful tool to study these processes with very high angular resolution. This type of emission has been confirmed in objects with L {sub bol} ≳ 1 L {sub ⊙}. Objects with lower luminosities also undergo mass-loss and accretion, and thus, are prospective sites of maser emission.more » Our sensitive single-dish observations provided a single detection when pointing toward the FHC L1448 IRS 2E. However, follow-up interferometric observations showed water maser emission associated with the nearby YSO L1448 IRS 2 (a Class 0 protostar of L {sub bol} ≃ 3.6–5.3 L {sub ⊙}) and did not find any emission toward L1448 IRS 2E. The upper limits for water maser emission determined by our observations are one order of magnitude lower than expected from the correlation between water maser luminosities and bolometric luminosities found for YSOs. This suggests that this correlation does not hold at the lower end of the (sub)stellar mass spectrum. Possible reasons are that the slope of this correlation is steeper at L {sub bol} ≤ 1 L {sub ⊙} or that there is an absolute luminosity threshold below which water maser emission cannot be produced. Alternatively, if the correlation still stands at low luminosity, the detection rates of masers would be significantly lower than the values obtained in higher-luminosity Class 0 protostars.« less

Mass-Radius Relationships for Low-Mass Planets: From Iron Planets to Water Planets

NASA Technical Reports Server (NTRS)

Kuchner, Marc

2007-01-01

Transit observations, and radial velocity measurements, have begun to populate the mass radius diagram for extrasolar planets; fubture astrometric measurements and direct images promise more mass and radius information. Clearly, the bulk density of a planet indicates something about a planet s composition--but what? I will attempt to answer this question in general for low-mass planets (mass) using a combination of analytic and numerical calculations, and I will show that all low-mass planets obey a kind of universal mass-radius relationship: an expansion whose first term is M approx. R(sup 3).

Individual hemoglobin mass response to normobaric and hypobaric "live high-train low": A one-year crossover study.

PubMed

Hauser, Anna; Troesch, Severin; Saugy, Jonas J; Schmitt, Laurent; Cejuela-Anta, Roberto; Faiss, Raphael; Steiner, Thomas; Robinson, Neil; Millet, Grégoire P; Wehrlin, Jon P

2017-08-01

The purpose of this research was to compare individual hemoglobin mass (Hb mass ) changes following a live high-train low (LHTL) altitude training camp under either normobaric hypoxia (NH) or hypobaric hypoxia (HH) conditions in endurance athletes. In a crossover design with a one-year washout, 15 male triathletes randomly performed two 18-day LHTL training camps in either HH or NH. All athletes slept at 2,250 meters and trained at altitudes <1,200 meters. Hb mass was measured in duplicate with the optimized carbon monoxide rebreathing method before (pre) and immediately after (post) each 18-day training camp. Hb mass increased similarly in HH (916-957 g, 4.5 ± 2.2%, P < 0.001) and in NH (918-953 g, 3.8 ± 2.6%, P < 0.001). Hb mass changes did not differ between HH and NH ( P = 0.42). There was substantial interindividual variability among subjects to both interventions (i.e., individual responsiveness or the individual variation in the response to an intervention free of technical noise): 0.9% in HH and 1.7% in NH. However, a correlation between intraindividual ΔHb mass changes (%) in HH and in NH ( r = 0.52, P = 0.048) was observed. HH and NH evoked similar mean Hb mass increases following LHTL. Among the mean Hb mass changes, there was a notable variation in individual Hb mass response that tended to be reproducible. NEW & NOTEWORTHY This is the first study to compare individual hemoglobin mass (Hb mass ) response to normobaric and hypobaric live high-train low using a same-subject crossover design. The main findings indicate that hypobaric and normobaric hypoxia evoked a similar mean increase in Hb mass following 18 days of live high-train low. Notable variability and reproducibility in individual Hb mass responses between athletes was observed, indicating the importance of evaluating individual Hb mass response to altitude training. Copyright © 2017 the American Physiological Society.

A Structural Analysis on Korean Young Children's Mathematical Ability and Its Related Children's and Mothers' Variables

ERIC Educational Resources Information Center

Lee, Hye Jung; Kim, Jihyun

2016-01-01

The objective of this study is to examine the structural relationships among variables that predict the mathematical ability of young children, namely young children's mathematical attitude, exposure to private mathematical learning, mothers' view about their children's mathematical learning, and mothers' mathematical attitude. To this end, we…

Low bone mass prevalence and osteoporosis risk factor assessment in African American Wisconsin women.

PubMed

Kidambi, Srividya; Partington, Susan; Binkley, Neil

2005-11-01

Post-menopausal osteoporosis is seen in all racial groups. With the increasing population and longevity of minority groups, osteoporosis is becoming an important health concern. Data regarding risk factors for, and prevalence of, low bone mass and awareness of osteoporosis risk in African American (AA) women are limited. This article evaluates the risk factors for, and prevalence of, low bone mass in a population of urban AA women in Wisconsin and assesses this group's perceived risk for osteoporosis. One hundred fifty consecutive community-dwelling AA women > or = 45 years old from Milwaukee, Wis were asked to complete a questionnaire based on currently accepted osteoporosis risk factors. Additionally, their perception of osteoporosis risk was assessed using a Likert scale. All subjects underwent quantitative calcaneal ultrasound. Subject mean age was 54 +/- 7 years. Mean T- and Z-scores were 0.5 and 0.4, respectively. Applying World Health Organization criteria, osteopenia (bone mineral density T-score <-1.0) was present in 23.3% and osteoporosis (bone mineral density <-2.5) in 9.3%. Multivariate analysis of risk factors showed that lifetime incidence of at least 1 fracture, multiparity (>2 children), postmenopausal state, and current smoking were associated with lower calcaneal bone mass. Higher education and presence of diabetes were associated with a higher bone mass. Only 25% of the women surveyed thought they were at moderate to high risk for osteoporosis. Low bone mass was present in 33% of these AA women despite their relative young age. Many AA women do not perceive osteoporosis as a health risk. It is necessary to develop strategies to educate AA women regarding osteoporosis risk.

Planet hunters. VII. Discovery of a new low-mass, low-density planet (PH3 C) orbiting Kepler-289 with mass measurements of two additional planets (PH3 B and D)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmitt, Joseph R.; Fischer, Debra A.; Wang, Ji

2014-11-10

We report the discovery of one newly confirmed planet (P = 66.06 days, R {sub P} = 2.68 ± 0.17 R {sub ⊕}) and mass determinations of two previously validated Kepler planets, Kepler-289 b (P = 34.55 days, R {sub P} = 2.15 ± 0.10 R {sub ⊕}) and Kepler-289-c (P = 125.85 days, R {sub P} = 11.59 ± 0.10 R {sub ⊕}), through their transit timing variations (TTVs). We also exclude the possibility that these three planets reside in a 1:2:4 Laplace resonance. The outer planet has very deep (∼1.3%), high signal-to-noise transits, which puts extremely tight constraintsmore » on its host star's stellar properties via Kepler's Third Law. The star PH3 is a young (∼1 Gyr as determined by isochrones and gyrochronology), Sun-like star with M {sub *} = 1.08 ± 0.02 M {sub ☉}, R {sub *} = 1.00 ± 0.02 R {sub ☉}, and T {sub eff} = 5990 ± 38 K. The middle planet's large TTV amplitude (∼5 hr) resulted either in non-detections or inaccurate detections in previous searches. A strong chopping signal, a shorter period sinusoid in the TTVs, allows us to break the mass-eccentricity degeneracy and uniquely determine the masses of the inner, middle, and outer planets to be M = 7.3 ± 6.8 M {sub ⊕}, 4.0 ± 0.9M {sub ⊕}, and M = 132 ± 17 M {sub ⊕}, which we designate PH3 b, c, and d, respectively. Furthermore, the middle planet, PH3 c, has a relatively low density, ρ = 1.2 ± 0.3 g cm{sup –3} for a planet of its mass, requiring a substantial H/He atmosphere of 2.1{sub −0.3}{sup +0.8}% by mass, and joins a growing population of low-mass, low-density planets.« less

Identification of Young Stellar Variables with KELT for K2 . I. Taurus Dippers and Rotators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodriguez, Joseph E.; Cargile, Phillip A.; Ansdell, Megan

One of the most well-studied young stellar associations, Taurus–Auriga, was observed by the extended Kepler mission, K2 , in the spring of 2017. K2 Campaign 13 (C13) is a unique opportunity to study many stars in this young association at high photometric precision and cadence. Using observations from the Kilodegree Extremely Little Telescope (KELT) survey, we identify “dippers,” aperiodic and periodic variables among K2 C13 target stars. This release of the KELT data (light curve data in e-tables) provides the community with long-time baseline observations to assist in the understanding of the more exotic variables in the association. Transient-like phenomenamore » on timescales of months to years are known characteristics in the light curves of young stellar objects, making contextual pre- and post- K2 observations critical to understanding their underlying processes. We are providing a comprehensive set of the KELT light curves for known Taurus–Auriga stars in K2 C13. The combined data sets from K2 and KELT should permit a broad array of investigations related to star formation, stellar variability, and protoplanetary environments.« less

The rotational velocity of low-mass stars in the Pleiades cluster

NASA Astrophysics Data System (ADS)

Queloz, D.; Allain, S.; Mermilliod, J.-C.; Bouvier, J.; Mayor, M.

1998-07-01

We present new {vsin i} measurements for 235 low-mass stars in the Pleiades. The differential rotational broadening has been resolved for all the stars in our sample. These results, combined with previously published measurements, provide a complete and unbiased rotation data set for stars in the mass range from 0.6 to 1.2{Msun}. Applying a numerical inversion technique on the {vsin i} distributions, we derive the distributions of equatorial velocities for low-mass Pleiades members. We find that half of the Pleiades dwarfs with a mass between 0.6 to 1 {Msun} have rotation rates lower than 10{ km s(-1) }. Comparison of the rotational distributions of low-mass members between IC 2602/2391 (~ 35 Myr) and the Pleiades (~ 100 Myr) suggests that G dwarfs behave like solid-bodies and follow Skumanich's law during this time span. However, comparison between Pleiades and older clusters -M34 (~ 200 Myr) and Hyades (~ 600 Myr)- indicates that the braking of slow rotators on the early main sequence is weaker than predicted by an asymptotical Skumanich's law. This strongly supports the view that angular momentum tapped in the radiative core of slow rotators on the zero age main sequence (ZAMS) resurfaces into the convective envelope between Pleiades and Hyades age. For the G-dwarfs, we derive a characteristic coupling time scale between the core and the envelope of about 100-200 Myr, which accounts for the observed evolution of surface rotation from the ZAMS to the Hyades. The relationship between rotation and coronal activity in the Pleiades is in agreement with previous observations in other clusters and field stars. We show that the Rossby diagram provides an excellent description of the X-ray activity for all stars in the mass domain studied. The Pleiades data for slow and moderate rotators fills the gap between the X-ray-rotation correlation found for slow rotators and the X-ray ``saturation plateau'' observed for young fast rotators. The transition between increasing X

Complexity of food preparation and food security status in low-income young women.

PubMed

Engler-Stringer, Rachel; Stringer, Bernadette; Haines, Ted

2011-01-01

This study was conducted to explore whether preparing more complex meals was associated with higher food security status. This mixed-methods, community-based study involved the use of semistructured interviews to examine the cooking practices of a group of young, low-income women in Montreal. Fifty participants aged 18 to 35 were recruited at 10 locations in five low-income neighbourhoods. Food security status was the main outcome measure and the main exposure variable, "complex food preparation," combined the preparation of three specific food types (soups, sauces, and baked goods) using basic ingredients. Low-income women preparing a variety of meals using basic ingredients at least three times a week were more than twice as likely to be food secure as were women preparing more complex meals less frequently. Women who prepared more complex meals more frequently had higher food security. Whether this means that preparing more complex foods results in greater food security remains unclear, as this was an exploratory study.

X-ray Emission from Seyfert 2 Galaxies with Low-Mass Black Holes

NASA Astrophysics Data System (ADS)

Barth, Aaron

2005-10-01

We have recently identified the first sample of Seyfert 2 nuclei in host galaxies with stellar velocity dispersions smaller than 60 km/s, as a way to detect and study black holes with likely masses below 10^6 solar masses. These galaxies are Type 2 analogs of "dwarf" Seyfert 1 galaxies such as NGC 4395 and POX 52. We propose to obtain XMM exposures of four Seyfert 2 galaxies with stellar velocity dispersions in the range 25-47 km/s in order to (a) determine X-ray luminosities as part of an overall program to measure the SEDs of these sources; (b) determine the amount of X-ray absorption to establish whether these are obscured versions of NLS1 galaxies; (c) search for variability, which is expected for AGNs with very low black hole masses.

Confirmation of the binary status of Chamaeleon Hα 2 - a very young low-mass binary in Chamaeleon

NASA Astrophysics Data System (ADS)

Schmidt, T. O. B.; Neuhäuser, R.; Vogt, N.; Seifahrt, A.; Roell, T.; Bedalov, A.

2008-06-01

Context: Neuhäuser & Comerón (1998, Science, 282, 83; 1999, A&A, 350, 612) presented direct imaging evidence, as well as first spectra, of several young stellar and sub-stellar M6- to M8-type objects in the Cha I dark cloud. One of these objects is Cha Hα 2, classified as brown dwarf candidate in several publications and suggested as possible binary in Neuhäuser et al. (2002, A&A, 384, 999). Aims: We have searched around Cha Hα 2 for close and faint companions with adaptive optics imaging. Methods: Two epochs of direct imaging data were taken with the Very Large Telescope (VLT) Adaptive Optics instrument NACO in February 2006 and March 2007 in Ks-band together with a Hipparcos binary for astrometric calibration. Moreover, we took a J-band image in March 2007 to get color information. We retrieved an earlier image from 2005 from the European Southern Observatory (ESO) Science Archive Facility, increasing the available time coverage. After confirmation of common proper motion, we deduce physical parameters of the objects by spectroscopy, like temperature and mass. Results: We find Cha Hα 2 to be a very close binary of 0.16 arcsec separation, having a flux ratio of 0.91, thus having almost equal brightness and indistinguishable spectral types within the errors. We show that the two tentative components of Cha Hα 2 form a common proper motion pair, and that neither component is a non-moving background object. We even find evidence for orbital motion. A combined spectrum of both stars spanning optical and near-infrared parts of the spectral energy distribution yields a temperature of 3000 ± 100 K, corresponding to a spectral type of M6 ± 1 and a surface gravity of log{g} = 4.0+0.75-0.5, both from a comparison with GAIA model atmospheres. Furthermore, we obtained an optical extinction of AV ≃ 4.3 mag from this comparison. Conclusions: We derive masses of 0.110 M⊙ (≥0.070 M⊙) and 0.124 M⊙ (≥0.077 M⊙) for the two components of Cha Hα 2, i

VizieR Online Data Catalog: Spectroscopy of very low mass objects (Patience+, 2012)

NASA Astrophysics Data System (ADS)

Patience, J.; King, R. R.; De Rosa, R. J.; Vigan, A.; Witte, S.; Rice, E.; Helling, C.; Hauschildt, P.

2012-09-01

With a uniform VLT SINFONI data set of nine targets, we have developed an empirical grid of J, H, K spectra of the atmospheres of objects estimated to have very low substellar masses of ~5-20MJup and young ages ranging from ~1-50Myr. Most of the targets are companions, objects which are especially valuable for comparison with atmosphere and evolutionary models, as they present rare cases in which the age is accurately known from the primary. Based on the youth of the sample, all objects are expected to have low surface gravity, and this study investigates the critical early phases of the evolution of substellar objects. The spectra are compared with grids of five different theoretical atmosphere models. ************************************************************************** * * * Sorry, but the author(s) never supplied the tabular material * * announced in the paper * * * **************************************************************************

The Survey of HI in Extremely Low-mass Dwarfs: A Multi-Wavelength Perspective on Low-Mass Galaxy Evolution

NASA Astrophysics Data System (ADS)

Cannon, John M.; McNichols, Andrew; Teich, Yaron; Adams, Elizabeth A.; Giovanelli, Riccardo; Haynes, Martha P.; McQuinn, Kristen B.; Salzer, John Joseph; Skillman, Evan D.; Dolphin, Andrew E.; Elson, Edward C.; Haurberg, Nathalie C.; Huang, Shan; Janowiecki, Steven; Jozsa, Gyula; Leisman, Luke; Ott, Juergen; Papastergis, Emmanouil; Rhode, Katherine L.; Saintonge, Amelie; Van Sistine, Angela; Warren, Steven R.

2017-01-01

The “Survey of HI in Extremely Low-mass Dwarfs” (SHIELD) is a multiwavelength study of local volume low-mass galaxies drawn from the Arecibo Legacy Fast ALFA (ALFALFA) catalog. HST/Spitzer joint program GO-12658 revealed the stellar populations of the first 12 SHIELD galaxies (Cannon et al. 2011), allowing accurate distance measurements (McQuinn et al. 2014) and detailed studies of the patterns of recent star formation in each galaxy (McQuinn et al. 2015). These HST and Spitzer images are a critical interpretive benchmark for ground-based optical imaging and spectroscopy (Haurberg et al. 2015), as well as for sensitive VLA HI spectral line imaging of the SHIELD galaxies (McNichols et al. 2016; Teich et al. 2016). These results have furthered our understanding of the evolution of galaxies in a mass regime that was previously only sparsely populated. With the low-redshift ALFALFA catalog now complete, the scope of the SHIELD program has been expanded to include all 82 galaxies that meet distance, line width, and HI flux criteria for being gas-rich, low-mass galaxies. In HST program 13750, images of 18 more SHIELD galaxies have again set the physical scales for supporting HI spectral line imaging with both the VLA and the WSRT (Gordon et al. 2016). Taken as a whole, the ongoing SHIELD program is one of the most comprehensive multiwavelength studies of the physical properties of low-mass galaxies outside of the Local Group.

Identifying Psychosocial Variables That Predict Safer Sex Intentions in Adolescents and Young Adults

PubMed Central

Brüll, Phil; Ruiter, Robert A. C.; Wiers, Reinout W.; Kok, Gerjo

2016-01-01

Young people are especially vulnerable to sexually transmitted infections (STIs). The triad of deliberate and effective safer sex behavior encompasses condom use, combined with additional information about a partner’s sexual health, and the kind of sex acts usually performed. To identify psychosocial predictors of young people’s intentions to have safer sex, as related to this triad, we conducted an online study with 211 sexually active participants aged between 18 and 24 years. Predictors [i.e., perceived behavioral control (PBC), subjective norms, and intention] taken from Fishbein and Ajzen’s Reasoned Action Approach (RAA), were combined with more distal variables (e.g., behavioral inhibition, sensation seeking, parental monitoring, and knowledge about STIs). Beyond the highly predictive power of RAA variables, additional variance was explained by the number of instances of unprotected sexual intercourse (SI) during the last 12 months and reasons for using barrier protection during first SI. In particular, past condom non-use behavior moderated PBC related to intended condom use. Further, various distal variables showed significant univariate associations with intentions related to the three behaviors of interest. It may, therefore, be helpful to include measures of past behavior as well as certain additional distal variables in future safer sex programs designed to promote health-sustaining sexual behavior. PMID:27148520

Tri-Ponderal Mass Index vs. Fat Mass/Height³ as a Screening Tool for Metabolic Syndrome Prediction in Colombian Children and Young People.

PubMed

Ramírez-Vélez, Robinson; Correa-Bautista, Jorge Enrique; Carrillo, Hugo Alejandro; González-Jiménez, Emilio; Schmidt-RioValle, Jacqueline; Correa-Rodríguez, María; García-Hermoso, Antonio; González-Ruíz, Katherine

2018-03-27

Tri-ponderal mass index (TMI) and fat mass index (FMI) have been proposed as alternative approaches for assessing body fat since BMI does not ensure an accurate screening for obesity and overweight status in children and adolescents. This study proposes thresholds of the TMI and FMI for the prediction of metabolic syndrome (MetS) in children and young people. For this purpose, a cross-sectional study was conducted on 4673 participants (57.1% females), who were 9-25 years of age. As part of the study, measurements of the subjects' weight, waist circumference, serum lipid indices, blood pressure and fasting plasma glucose were taken. Body composition was measured by bioelectrical impedance analysis (BIA). The TMI and FMI were calculated as weight (kg)/height (m³) and fat mass (kg)/height (m³), respectively. Following the International Diabetes Federation (IDF) definition, MetS is defined as including three or more metabolic abnormalities. Cohort-specific thresholds were established to identify Colombian children and young people at high risk of MetS. The thresholds were applied to the following groups: (i) a cohort of children where the girls' TMI ≥ 12.13 kg/m³ and the boys' TMI ≥ 12.10 kg/m³; (ii) a cohort of adolescents where the girls' TMI ≥ 12.48 kg/m³ and the boys' TMI ≥ 11.19 kg/m³; (iii) a cohort of young adults where the women's TMI ≥ 13.21 kg/m³ and the men's TMI ≥ 12.19 kg/m³. The FMI reference cut-off values used for the different groups were as follows: (i) a cohort of children where the girls' FMI ≥ 2.59 fat mass/m³ and the boys' FMI ≥ 1.98 fat mass/m³; (ii) a cohort of adolescents where the girls' FMI ≥ 3.12 fat mass/m³ and the boys' FMI ≥ 1.46 fat mass/m³; (iii) a cohort of adults where the women's FMI ≥ 3.27 kg/m³ and the men's FMI ≥ 1.65 kg/m³. Our results showed that the FMI and TMI had a moderate discriminatory power to detect MetS in Colombian children, adolescents, and young adults.

The Mass Distribution of Companions to Low-mass White Dwarfs

NASA Astrophysics Data System (ADS)

Andrews, Jeff J.; Price-Whelan, Adrian M.; Agüeros, Marcel A.

2014-12-01

Measuring the masses of companions to single-line spectroscopic binary stars is (in general) not possible because of the unknown orbital plane inclination. Even when the mass of the visible star can be measured, only a lower limit can be placed on the mass of the unseen companion. However, since these inclination angles should be isotropically distributed, for a large enough, unbiased sample, the companion mass distribution can be deconvolved from the distribution of observables. In this work, we construct a hierarchical probabilistic model to infer properties of unseen companion stars given observations of the orbital period and projected radial velocity of the primary star. We apply this model to three mock samples of low-mass white dwarfs (LMWDs; M <~ 0.45 M ⊙) and a sample of post-common-envelope binaries. We use a mixture of two Gaussians to model the WD and neutron star (NS) companion mass distributions. Our model successfully recovers the initial parameters of these test data sets. We then apply our model to 55 WDs in the extremely low-mass (ELM) WD Survey. Our maximum a posteriori model for the WD companion population has a mean mass μWD = 0.74 M ⊙, with a standard deviation σWD = 0.24 M ⊙. Our model constrains the NS companion fraction f NS to be <16% at 68% confidence. We make samples from the posterior distribution publicly available so that future observational efforts may compute the NS probability for newly discovered LMWDs.

Star Formation in low mass galaxies

NASA Astrophysics Data System (ADS)

Mehta, Vihang

2018-01-01

Our current hierarchical view of the universe asserts that the large galaxies we see today grew via mergers of numerous smaller galaxies. As evidenced by recent literature, the collective impact of these low mass galaxies on the universe is more substantial than previously thought. Studying the growth and evolution of these low mass galaxies is critical to our understanding of the universe as a whole. Star formation is one of the most important ongoing processes in galaxies. Forming stars is fundamental to the growth of a galaxy. One of the main goals of my thesis is to analyze the star formation in these low mass galaxies at different redshifts.Using the Hubble UltraViolet Ultra Deep Field (UVUDF), I investigate the star formation in galaxies at the peak of the cosmic star formation history using the ultraviolet (UV) light as a star formation indicator. Particularly, I measure the UV luminosity function (LF) to probe the volume-averaged star formation properties of galaxies at these redshifts. The depth of the UVUDF is ideal for a direct measurement of the faint end slope of the UV LF. This redshift range also provides a unique opportunity to directly compare UV to the "gold standard" of star formation indicators, namely the Hα nebular emission line. A joint analysis of the UV and Hα LFs suggests that, on average, the star formation histories in low mass galaxies (~109 M⊙) are more bursty compared to their higher mass counterparts at these redshifts.Complementary to the analysis of the average star formation properties of the bulk galaxy population, I investigate the details of star formation in some very bursty galaxies at lower redshifts selected from Spitzer Large Area Survey with Hyper-Suprime Cam (SPLASH). Using a broadband color-excess selection technique, I identify a sample of low redshift galaxies with bright nebular emission lines in the Subaru-XMM Deep Field (SXDF) from the SPLASH-SXDF catalog. These galaxies are highly star forming and have

Reevaluating the Mass-Radius Relation for Low-mass, Main-sequence Stars

NASA Astrophysics Data System (ADS)

Feiden, Gregory A.; Chaboyer, Brian

2012-09-01

We examine the agreement between the observed and theoretical low-mass (<0.8 M ⊙) stellar main-sequence mass-radius relationship by comparing detached eclipsing binary (DEB) data with a new, large grid of stellar evolution models. The new grid allows for a realistic variation in the age and metallicity of the DEB population, characteristic of the local galactic neighborhood. Overall, our models do a reasonable job of reproducing the observational data. A large majority of the models match the observed stellar radii to within 4%, with a mean absolute error of 2.3%. These results represent a factor of two improvement compared to previous examinations of the low-mass mass-radius relationship. The improved agreement between models and observations brings the radius deviations within the limits imposed by potential starspot-related uncertainties for 92% of the stars in our DEB sample.

SEARCHING FOR YOUNG M DWARFS WITH GALEX

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shkolnik, Evgenya L.; Weinberger, Alycia J.; Liu, Michael C.

2011-01-20

The census of young moving groups in the solar neighborhood is significantly incomplete in the low-mass regime. We have developed a new selection process to find these missing members based on the Galaxy Evolution Explorer (GALEX) All-Sky Imaging Survey (AIS). For stars with spectral types {approx}>K5 (R - J {approx}> 1.5) and younger than {approx}300 Myr, we show that near-UV (NUV) and far-UV (FUV) emission is greatly enhanced above the quiescent photosphere, analogous to the enhanced X-ray emission of young low-mass stars seen by ROSAT but detectable to much larger distances with GALEX. By combining GALEX data with optical (HSTmore » Guide Star Catalog) and near-IR (2MASS) photometry, we identified an initial sample of 34 young M dwarf candidates in a 1000 deg{sup 2} region around the {approx}10 Myr TW Hydra Association (TWA). Low-resolution spectroscopy of 30 of these found 16 which had H{alpha} in emission, which were then followed up at high resolution to search for spectroscopic evidence of youth and to measure their radial velocities. Four objects have low surface gravities, photometric distances and space motions consistent with TWA, but the non-detection of Li indicates that they may be too old to belong to this moving group. One object (M3.5, 93 {+-} 19 pc) appears to be the first known accreting low-mass member of the {approx}15 Myr Lower Centaurus Crux OB association. Two objects exhibit all the characteristics of the known TWA members, and thus we designate them as TWA 31 (M4.2, 110 {+-} 11 pc) and TWA 32 (M6.3, 53 {+-} 5 pc). TWA 31 shows extremely broad (447 km s{sup -1}) H{alpha} emission, making it the sixth member of TWA found to have ongoing accretion. TWA 32 is resolved into a 0.''6 binary in Keck laser guide star adaptive optics imaging. Our search should be sensitive down to spectral types of at least M4-M5 in TWA and thus the small numbers of new member is puzzling. This might indicate TWA has an atypical mass function or that the presence

Exploring Our Low-Mass Neighbors

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-10-01

The Karl G. Jansky Very Large Array, located in Socorro, NM. [John Fowler]Taking advantage of a program offered by the National Radio Astronomy Observatory (NRAO), an undergraduate class has observed local dwarf galaxies to learn about their properties.The Benefits of Nearby DwarfsIf you want to learn about the physical properties of low-mass galactic halos, the best place to look is nearby dwarf galaxies. These objects have the benefit of being close enough that we can resolve individual stars, allowing us to explore the relationship between star formation and the surrounding interstellar medium. They also allow us to directly measure bulk velocities, so we can interpret the distributions of both dark and baryonic matt5ter in these galaxies.HI images of UGC 11411. Left: HI mass surface density. Right: the intensity-weighted velocity field of the HI gas, which reveals the bulk kinematics of the galaxy. [Bralts-Kelly et al. 2017]Though thousands of local-volume, gas-rich objects have been explored by gas surveys in the past, many have slipped through the cracks due to the varied selection criteria of these different surveys. In a new study, neutral atomic hydrogen observations are presented for the first time for two of these star-forming, gas-rich dwarf galaxies.A Class in ActionGuided by Professor John Cannon and collaborators at other universities, a class of undergraduates at Macalester College in St. Paul, Minnesota, has coauthored a study of the neutral interstellar medium of these two local dwarf galaxies. The project was made possible by the Observing for University Classes program offered by NRAOs Karl G. Jansky Very Large Array (VLA), in which university classes in observational astronomy can apply for observing time with the VLA.Top: a view of UGC 11411s stars from Hubble. Middle: the locations of the galaxys star formation, as traced by SAOs telescopes observations of H. Bottom: UGC 11411s neutral interstellar medium distribution (red contour), overlaid

Association of Body Mass Index with Depression, Anxiety and Suicide—An Instrumental Variable Analysis of the HUNT Study

PubMed Central

Bjørngaard, Johan Håkon; Carslake, David; Lund Nilsen, Tom Ivar; Linthorst, Astrid C. E.; Davey Smith, George; Gunnell, David; Romundstad, Pål Richard

2015-01-01

Objective While high body mass index is associated with an increased risk of depression and anxiety, cumulative evidence indicates that it is a protective factor for suicide. The associations from conventional observational studies of body mass index with mental health outcomes are likely to be influenced by reverse causality or confounding by ill-health. In the present study, we investigated the associations between offspring body mass index and parental anxiety, depression and suicide in order to avoid problems with reverse causality and confounding by ill-health. Methods We used data from 32,457 mother-offspring and 27,753 father-offspring pairs from the Norwegian HUNT-study. Anxiety and depression were assessed using the Hospital Anxiety and Depression Scale and suicide death from national registers. Associations between offspring and own body mass index and symptoms of anxiety and depression and suicide mortality were estimated using logistic and Cox regression. Causal effect estimates were estimated with a two sample instrument variable approach using offspring body mass index as an instrument for parental body mass index. Results Both own and offspring body mass index were positively associated with depression, while the results did not indicate any substantial association between body mass index and anxiety. Although precision was low, suicide mortality was inversely associated with own body mass index and the results from the analysis using offspring body mass index supported these results. Adjusted odds ratios per standard deviation body mass index from the instrumental variable analysis were 1.22 (95% CI: 1.05, 1.43) for depression, 1.10 (95% CI: 0.95, 1.27) for anxiety, and the instrumental variable estimated hazard ratios for suicide was 0.69 (95% CI: 0.30, 1.63). Conclusion The present study’s results indicate that suicide mortality is inversely associated with body mass index. We also found support for a positive association between body mass index

Association of Body Mass Index with Depression, Anxiety and Suicide-An Instrumental Variable Analysis of the HUNT Study.

PubMed

Bjørngaard, Johan Håkon; Carslake, David; Lund Nilsen, Tom Ivar; Linthorst, Astrid C E; Davey Smith, George; Gunnell, David; Romundstad, Pål Richard

2015-01-01

While high body mass index is associated with an increased risk of depression and anxiety, cumulative evidence indicates that it is a protective factor for suicide. The associations from conventional observational studies of body mass index with mental health outcomes are likely to be influenced by reverse causality or confounding by ill-health. In the present study, we investigated the associations between offspring body mass index and parental anxiety, depression and suicide in order to avoid problems with reverse causality and confounding by ill-health. We used data from 32,457 mother-offspring and 27,753 father-offspring pairs from the Norwegian HUNT-study. Anxiety and depression were assessed using the Hospital Anxiety and Depression Scale and suicide death from national registers. Associations between offspring and own body mass index and symptoms of anxiety and depression and suicide mortality were estimated using logistic and Cox regression. Causal effect estimates were estimated with a two sample instrument variable approach using offspring body mass index as an instrument for parental body mass index. Both own and offspring body mass index were positively associated with depression, while the results did not indicate any substantial association between body mass index and anxiety. Although precision was low, suicide mortality was inversely associated with own body mass index and the results from the analysis using offspring body mass index supported these results. Adjusted odds ratios per standard deviation body mass index from the instrumental variable analysis were 1.22 (95% CI: 1.05, 1.43) for depression, 1.10 (95% CI: 0.95, 1.27) for anxiety, and the instrumental variable estimated hazard ratios for suicide was 0.69 (95% CI: 0.30, 1.63). The present study's results indicate that suicide mortality is inversely associated with body mass index. We also found support for a positive association between body mass index and depression, but not for anxiety.

Infrared Detection of Very Low Mass Stars.

NASA Astrophysics Data System (ADS)

Probst, Ronald George

We present in this thesis a review of very-low -mass ((TURN)0.1 M(,0)) star research, and results of two observational programs directed at the photometric detection of low mass binary companions in the infrared. Present theoretical desiderata are model atmospheres for very cool dwarf stars and determination of the minimum protostellar mass with all relevant physics included. Luminosities for these stars are well determined, but the effective temperature scale is uncertain and abundance analyses are lacking. Masses are known for very few, and with large relative errors. The luminosity function for M(,v) > 13 is very uncertain. Astrometric methods provide at present the only means of detecting very low mass objects in significant numbers. Completion of the near-star parallax catalogue and measurement of additional low-mass binaries are important observational programs. The potential of photometric selection of red dwarf binaries is explored in Chapter II. Separation of binaries from single stars by color anomalies alone is found impractical. Detection by overluminosity in the HR diagram is hampered by the intrinsic spread of the field star population. However, we find that application of both kinematic and photometric criteria allows binaries to be detected with only moderate contamination by single stars; we discuss several binary suspects selected in this way. Our approach uses an infrared bandpass to provide temperature resolution in the color baseline, and we present JHK photometry for 60 stars, including recent parallax stars with M(,v)>14. We examine the status of the least luminous stars; there is no conclusive evidence that they are not hydrogen-burning objects. Chapter III presents a survey of (TURN)100 white dwarfs at 2 (mu) for infrared excess indicative of low -luminosity cool companions. White dwarf-red dwarf composites are detectable by infared color anomalies down to M(,v)(TURN)21 for the red dwarf component, and our survey is complete to absolute

Proposal for new diagnostic criteria for low skeletal muscle mass based on computed tomography imaging in Asian adults.

PubMed

Hamaguchi, Yuhei; Kaido, Toshimi; Okumura, Shinya; Kobayashi, Atsushi; Hammad, Ahmed; Tamai, Yumiko; Inagaki, Nobuya; Uemoto, Shinji

2016-01-01

Low skeletal muscle, referred to as sarcopenia, has been shown to be an independent predictor of lower overall survival in various kinds of diseases. Several studies have evaluated the low skeletal muscle mass using computed tomography (CT) imaging. However, the cutoff values based on CT imaging remain undetermined in Asian populations. Preoperative plain CT imaging at the third lumbar vertebrae level was used to measure the psoas muscle mass index (PMI, cm(2)/m(2)) in 541 adult donors for living donor liver transplantation (LDLT). We analyzed PMI distribution according to sex or donor age, and determined the sex-specific cutoff values of PMI to define low skeletal muscle mass. PMI in men was significantly higher than observed in women (8.85 ± 1.61 cm(2)/m(2) versus 5.77 ± 1.21 cm(2)/m(2); P < 0.001). PMI was significantly lower in individuals ≥50 y than in younger donors in both men and women (P < 0.001 and P < 0.001, respectively). On the basis of the younger donor data, we determined the sex-specific cutoff values for the low skeletal muscle mass were 6.36 cm(2)/m(2) for men and 3.92 cm(2)/m(2) for women (mean - 2 SD). Data from healthy young Asian adults were used to establish new criteria for low skeletal muscle mass that would be applicable for defining sarcopenia in Asian populations. Copyright © 2016 Elsevier Inc. All rights reserved.

Low-frequency variability of the Atlantic MOC in the eddying regime : the intrinsic component.

NASA Astrophysics Data System (ADS)

Gregorio, S.; Penduff, T.; Barnier, B.; Molines, J.-M.; Le Sommer, J.

2012-04-01

A 327-year 1/4° global ocean/sea-ice simulation has been produced by the DRAKKAR ocean modeling consortium. This simulation is forced by a repeated seasonal atmospheric forcing but nevertheless exhibits a substantial low-frequency variability (at interannual and longer timescales), which is therefore of intrinsic origin. This nonlinearly-generated intrinsic variability is almost absent from the coarse-resolution (2°) version of this simulation. Comparing the 1/4° simulation with its fully-forced counterpart, Penduff et al. (2011) have shown that the low-frequency variability of local sea-level is largely generated by the ocean itself in eddying areas, rather than directly forced by the atmosphere. Using the same simulations, the present study quantifies the imprint of the intrinsic low-frequency variability on the Meridional Overturning Circulation (MOC) at interannual-to-decadal timescales in the Atlantic. We first compare the intrinsic and atmospherically-forced interannual variances of the Atlantic MOC calculated in geopotential coordinates. This analysis reveals substantial sources of intrinsic MOC variability in the South Atlantic (driven by the Agulhas mesoscale activity according to Biastoch et al. (2008)), but also in the North Atlantic. We extend our investigation to the MOC calculated in isopycnal coordinates, and identify regions in the basin where the water mass transformation exhibits low-frequency intrinsic variability. In this eddy-permitting regime, intrinsic processes are shown to generate about half the total (geopotential and isopycnal) MOC interannual variance in certain key regions of the Atlantic. This intrinsic variability is absent from 2° simulations. Penduff, T., Juza, M., Barnier, B., Zika, J., Dewar, W.K., Treguier, A.-M., Molines, J.-M., Audiffren, N., 2011: Sea-level expression of intrinsic and forced ocean variabilities at interannual time scales. J. Climate, 24, 5652-5670. doi: 10.1175/JCLI-D-11-00077.1. Biastoch, A., Böning, C

The peculiar dipping events in the disc-bearing young-stellar object EPIC 204278916

NASA Astrophysics Data System (ADS)

Scaringi, S.; Manara, C. F.; Barenfeld, S. A.; Groot, P. J.; Isella, A.; Kenworthy, M. A.; Knigge, C.; Maccarone, T. J.; Ricci, L.; Ansdell, M.

2016-12-01

EPIC 204278916 has been serendipitously discovered from its K2 light curve that displays irregular dimmings of up to 65 per cent for ≈25 consecutive days out of 78.8 d of observations. For the remaining duration of the observations, the variability is highly periodic and attributed to stellar rotation. The star is a young, low-mass (M-type) pre-main-sequence star with clear evidence of a resolved tilted disc from Atacama Large Millimeter/submillimeter Array (ALMA) observations. We examine the K2 light curve in detail and hypothesize that the irregular dimmings are caused by either a warped inner disc edge or transiting cometary-like objects in either circular or eccentric orbits. The explanations discussed here are particularly relevant for other recently discovered young objects with similar absorption dips.

APEX-CHAMP+ high-J CO observations of low-mass young stellar objects. IV. Mechanical and radiative feedback

NASA Astrophysics Data System (ADS)

Yıldız, U. A.; Kristensen, L. E.; van Dishoeck, E. F.; Hogerheijde, M. R.; Karska, A.; Belloche, A.; Endo, A.; Frieswijk, W.; Güsten, R.; van Kempen, T. A.; Leurini, S.; Nagy, Z.; Pérez-Beaupuits, J. P.; Risacher, C.; van der Marel, N.; van Weeren, R. J.; Wyrowski, F.

2015-04-01

Context. During the embedded stage of star formation, bipolar molecular outflows and UV radiation from the protostar are important feedback processes. Both processes reflect the accretion onto the forming star and affect subsequent collapse or fragmentation of the cloud. Aims: Our aim is to quantify the feedback, mechanical and radiative, for a large sample of low-mass sources in a consistent manner. The outflow activity is compared to radiative feedback in the form of UV heating by the accreting protostar to search for correlations and evolutionary trends. Methods: Large-scale maps of 26 young stellar objects, which are part of the Herschel WISH key program are obtained using the CHAMP+ instrument on the Atacama Pathfinder EXperiment (12CO and 13CO 6-5; Eup ~ 100 K), and the HARP-B instrument on the James Clerk Maxwell Telescope (12CO and 13CO 3-2; Eup ~ 30 K). The maps have high spatial resolution, particularly the CO 6-5 maps taken with a 9″ beam, resolving the morphology of the outflows. The maps are used to determine outflow parameters and the results are compared with higher-J CO lines obtained with Herschel. Envelope models are used to quantify the amount of UV-heated gas and its temperature from 13CO 6-5 observations. Results: All sources in our sample show outflow activity, with the spatial extent decreasing from the Class 0 to the Class I stage. Consistent with previous studies, the outflow force, FCO, is larger for Class 0 sources than for Class I sources, even if their luminosities are comparable. The outflowing gas typically extends to much greater distances than the power-law envelope and therefore influences the surrounding cloud material directly. Comparison of the CO 6-5 results with HIFI H2O and PACS high-J CO lines, both tracing currently shocked gas, shows that the two components are linked, even though the transitions do not probe the same gas. The link does not extend down to CO 3-2. The conclusion is that CO 6-5 depends on the shock

Tri-Ponderal Mass Index vs. Fat Mass/Height3 as a Screening Tool for Metabolic Syndrome Prediction in Colombian Children and Young People

PubMed Central

Correa-Bautista, Jorge Enrique; Carrillo, Hugo Alejandro; Schmidt-RioValle, Jacqueline; González-Ruíz, Katherine

2018-01-01

Tri-ponderal mass index (TMI) and fat mass index (FMI) have been proposed as alternative approaches for assessing body fat since BMI does not ensure an accurate screening for obesity and overweight status in children and adolescents. This study proposes thresholds of the TMI and FMI for the prediction of metabolic syndrome (MetS) in children and young people. For this purpose, a cross-sectional study was conducted on 4673 participants (57.1% females), who were 9–25 years of age. As part of the study, measurements of the subjects’ weight, waist circumference, serum lipid indices, blood pressure and fasting plasma glucose were taken. Body composition was measured by bioelectrical impedance analysis (BIA). The TMI and FMI were calculated as weight (kg)/height (m3) and fat mass (kg)/height (m3), respectively. Following the International Diabetes Federation (IDF) definition, MetS is defined as including three or more metabolic abnormalities. Cohort-specific thresholds were established to identify Colombian children and young people at high risk of MetS. The thresholds were applied to the following groups: (i) a cohort of children where the girls’ TMI ≥ 12.13 kg/m3 and the boys’ TMI ≥ 12.10 kg/m3; (ii) a cohort of adolescents where the girls’ TMI ≥ 12.48 kg/m3 and the boys’ TMI ≥ 11.19 kg/m3; (iii) a cohort of young adults where the women’s TMI ≥ 13.21 kg/m3 and the men’s TMI ≥ 12.19 kg/m3. The FMI reference cut-off values used for the different groups were as follows: (i) a cohort of children where the girls’ FMI ≥ 2.59 fat mass/m3 and the boys’ FMI ≥ 1.98 fat mass/m3; (ii) a cohort of adolescents where the girls’ FMI ≥ 3.12 fat mass/m3 and the boys’ FMI ≥ 1.46 fat mass/m3; (iii) a cohort of adults where the women’s FMI ≥ 3.27 kg/m3 and the men’s FMI ≥ 1.65 kg/m3. Our results showed that the FMI and TMI had a moderate discriminatory power to detect MetS in Colombian children, adolescents, and young adults. PMID

Searching for Young M Dwarfs with GALEX

NASA Astrophysics Data System (ADS)

Shkolnik, Evgenya L.; Liu, Michael C.; Reid, I. Neill; Dupuy, Trent; Weinberger, Alycia J.

2011-01-01

The census of young moving groups in the solar neighborhood is significantly incomplete in the low-mass regime. We have developed a new selection process to find these missing members based on the Galaxy Evolution Explorer (GALEX) All-Sky Imaging Survey (AIS). For stars with spectral types gsimK5 (R - J >~ 1.5) and younger than ≈300 Myr, we show that near-UV (NUV) and far-UV (FUV) emission is greatly enhanced above the quiescent photosphere, analogous to the enhanced X-ray emission of young low-mass stars seen by ROSAT but detectable to much larger distances with GALEX. By combining GALEX data with optical (HST Guide Star Catalog) and near-IR (2MASS) photometry, we identified an initial sample of 34 young M dwarf candidates in a 1000 deg2 region around the ≈10 Myr TW Hydra Association (TWA). Low-resolution spectroscopy of 30 of these found 16 which had Hα in emission, which were then followed up at high resolution to search for spectroscopic evidence of youth and to measure their radial velocities. Four objects have low surface gravities, photometric distances and space motions consistent with TWA, but the non-detection of Li indicates that they may be too old to belong to this moving group. One object (M3.5, 93 ± 19 pc) appears to be the first known accreting low-mass member of the ≈15 Myr Lower Centaurus Crux OB association. Two objects exhibit all the characteristics of the known TWA members, and thus we designate them as TWA 31 (M4.2, 110 ± 11 pc) and TWA 32 (M6.3, 53 ± 5 pc). TWA 31 shows extremely broad (447 km s-1) Hα emission, making it the sixth member of TWA found to have ongoing accretion. TWA 32 is resolved into a 0farcs6 binary in Keck laser guide star adaptive optics imaging. Our search should be sensitive down to spectral types of at least M4-M5 in TWA and thus the small numbers of new member is puzzling. This might indicate TWA has an atypical mass function or that the presence of lithium absorption may be too restrictive a criteria for

The impact of body mass index on the prevalence of low back pain: the HUNT study.

PubMed

Heuch, Ingrid; Hagen, Knut; Heuch, Ivar; Nygaard, Øystein; Zwart, John-Anker

2010-04-01

A cross-sectional population-based study. To examine the association between body mass index and chronic low back pain, with adjustment for potential confounders. Although many studies have investigated this association, it is still unclear whether there is a general relationship between body mass index and low back pain which applies to all populations. This study is based on data collected in the HUNT 2 study in the county of Nord-Trøndelag in Norway between 1995 and 1997. Among a total of 92,936 persons eligible for participation, 30,102 men and 33,866 women gave information on body mass index and indicated whether they suffered from chronic low back pain (69% participation rate). A total of 6293 men (20.9%) and 8923 women (26.3%) experienced chronic low back pain. Relations were assessed by logistic regression of low back pain with respect to body mass index and other variables. In both sexes, a high body mass index was significantly associated with an increased prevalence of low back pain. In men the estimated OR per 5 kg/m increase in body mass index was 1.07 (95% CI: 1.03-1.12) and in women 1.17 (95% CI: 1.14-1.21), after adjustment for age, with a significantly stronger association in women. Additional adjustment for education, smoking status, leisure time physical activity, employment status, and activity at work hardly affected these associations. No interactions were found with most other factors. This large population-based study indicates that obesity is associated with a high prevalence of low back pain. Further studies are needed to determine if the association is causal.

Control of Precision Grip Force in Lifting and Holding of Low-Mass Objects

PubMed Central

Kimura, Daisuke; Kadota, Koji; Ito, Taro

2015-01-01

Few studies have investigated the control of grip force when manipulating an object with an extremely small mass using a precision grip, although some related information has been provided by studies conducted in an unusual microgravity environment. Grip-load force coordination was examined while healthy adults (N = 17) held a moveable instrumented apparatus with its mass changed between 6 g and 200 g in 14 steps, with its grip surface set as either sandpaper or rayon. Additional measurements of grip-force-dependent finger-surface contact area and finger skin indentation, as well as a test of weight discrimination, were also performed. For each surface condition, the static grip force was modulated in parallel with load force while holding the object of a mass above 30 g. For objects with mass smaller than 30 g, on the other hand, the parallel relationship was changed, resulting in a progressive increase in grip-to-load force (GF/LF) ratio. The rayon had a higher GF/LF force ratio across all mass levels. The proportion of safety margin in the static grip force and normalized moment-to-moment variability of the static grip force were also elevated towards the lower end of the object mass for both surfaces. These findings indicate that the strategy of grip force control for holding objects with an extremely small mass differs from that with a mass above 30 g. The data for the contact area, skin indentation, and weight discrimination suggest that a decreased level of cutaneous feedback signals from the finger pads could have played some role in a cost function in efficient grip force control with low-mass objects. The elevated grip force variability associated with signal-dependent and internal noises, and anticipated inertial force on the held object due to acceleration of the arm and hand, could also have contributed to the cost function. PMID:26376484

The effects of maternal psychosocial factors on parenting attitudes of low-income, single mothers with young children.

PubMed

Lutenbacher, M; Hall, L A

1998-01-01

Although recent evidence implies linkages among depression or depressive symptoms, self-esteem, history of childhood abuse, and parenting attitudes, the evidence does not clearly elucidate the relationships among these variables. To investigate the relationships among maternal psychosocial factors (history of childhood abuse, everyday stressors, self-esteem, and depressive symptoms) and parenting attitudes of low-income, single mothers who have young children. Secondary analyses of data from in-home interviews with 206 low-income, single mothers from a southeastern United States urban area were conducted. A variety of scales, including the Adult-Adolescent Parenting Inventory (AAPI), were used to measure maternal psychosocial factors. Using the AAPI, a Modified Parenting Attitudes Measure (MPAM), and subscales, a three-stage regression procedure was used to test the model. For stages 1 and 2, everyday stressors were the strongest predictor of self-esteem. Childhood sexual abuse, everyday stressors, low self-esteem, and control variables accounted for 58% of variance in depressive symptoms. In the third stage for the AAPI, only control variables were retained except in the Lack of Empathy subscale, where depressive symptoms and control variables accounted for 16% of the variance. The third stage for the MPAM yielded, by subscale: Only control variables predicted Corporal Punishment Beliefs; depressive symptoms were the strongest predictor for the total MPAM (19% of variance) and of the Inappropriate Emotional Expectations subscale (17%); and childhood physical abuse was the only predictor of Role Reversal. Depressive symptoms mediated the effects of childhood abuse, everyday stressors, and self-esteem and provided the linkage between these variables and at-risk parenting attitudes. Self-esteem decreased as everyday stressors increased but did not directly affect parenting attitudes. A relationship was not found between childhood abuse and low self-esteem. This study

Low-mass Stellar and Substellar Companions to sdB Stars

NASA Astrophysics Data System (ADS)

Geier, S.; Classen, L.; Brünner, P.; Nagel, K.; Schaffenroth, V.; Heuser, C.; Heber, U.; Drechsel, H.; Edelmann, H.; Koen, C.; O'Toole, S. J.; Morales-Rueda, L.

2012-03-01

It has been suggested that besides stellar companions, substellar objects in close orbits may be able to trigger mass loss in a common envelope phase and form hot subdwarfs. In an ongoing project we search for close substellar companions combining time resolved high resolution spectroscopy with photometry. We determine the fraction of as yet undetected radial velocity variable systems from a sample of 27 apparently single sdB stars to be ˜eq16%. We discovered low-mass stellar companions to the He-sdB CPD-20circ 1123 and the pulsator KPD 0629-0016. The brown dwarf reported to orbit the eclipsing binary SDSS J0820+0008 could be confirmed by an analysis of high resolution spectra taken with UVES. Reflection effects have been detected in the light curves of the known sdB binaries CPD -64circ 481 and BPS CS 22169-0001. The inclinations of these systems must be much higher than expected and the most likely companion masses are in the substellar regime. Finally, we determined the orbit of the sdB binary PHL 457, which has a very small radial velocity amplitude and may host the lowest mass substellar companion known. The implications of these new results for the open question of sdB formation are discussed.

A Deep X-ray Survey of Low-Mass PMS Stars in NGC 2264

NASA Technical Reports Server (NTRS)

Simon, Theodore

2005-01-01

Two X-ray images were obtained with the XMM-Newton spacecraft of more than 300 members of the NGC 2264 Open Cluster and its associated molecular cloud in order to investigate their magnetic activity. The X-ray fluxes extracted from those observations were used to study the dependence of stellar dynamo activity upon age and rotation for the optically revealed T Tauri stars and to place empirical constraints on theoretical models of angular momentum/dynamo evolution. The observations were also used to study the role of magnetic fields in the formation of low mass stars through the observation of very young protostars that are deeply embedded in the molecular cloud located behind the visible open cluster.

Weather and Rotation on Young Brown Dwarfs

NASA Astrophysics Data System (ADS)

Vos, Johanna; Biller, Beth; Allers, Katelyn; Manjavacas, Elena; Liu, Michael; Best, William; Metchev, Stanimir; Buenzli, Esther; Bonavita, Mariangela; Eriksson, Simon; Dupuy, Trent; Kopytova, Taisiya; Brandner, Wolfgang; Henning, Thomas; Bonnefoy, Mickael; Crossfield, Ian; Schlieder, Joshua; Homeier, Derek; Janson, Markus; Radigan, Jacqueline

2018-05-01

As part of a large, ground-based survey for weather patterns on exoplanet analogues, we have detected J-band variability in 5 young exoplanet analogues. We have already carried out followup Spitzer monitoring of two objects and here we propose Spitzer 3.6um and 4.5um monitoring of three early-mid-L detections in our survey. The proposed observations will enable us to assess the role of gravity in the variability properties of these young objects by providing a full measure of mid-IR amplitude across the full L spectral sequence for low-gravity objects. The proposed observations will also allow us to measure the rotational periods of our three targets. This will provide vital information on the angular momentum of young brown dwarfs, while enabling us to correct for geometric effects when considering the variability properties of our targets. This study will act as a necessary pathfinder for future variability studies of free-floating and companion exoplanets with JWST.

Astrometric confirmation of young low-mass binaries and multiple systems in the Chamaeleon star-forming regions

NASA Astrophysics Data System (ADS)

Vogt, N.; Schmidt, T. O. B.; Neuhäuser, R.; Bedalov, A.; Roell, T.; Seifahrt, A.; Mugrauer, M.

2012-10-01

masses twice as high as this value or more. Massive primary components appear to avoid the simultaneous formation of equal-mass secondary components, while extremely low-mass secondary components are hard to find for both high and low mass primaries owing to the much higher dynamic range and the faintness of the secondaries. Based on observations made with ESO telescopes at the Paranal Observatory under program IDs 076.C-0292(A), 078.C-0535(A), 080.C-0424(A), 082.C-0489(A), 084.C-0364(B), 086.C-0638(A) & 086.C-0600(B), the Hubble Space Telescope under program ID GO-8716 and data obtained from the ESO/ST-ECF Science Archive Facility from the Paranal Observatory under program IDs 075.C-0042(A), 076.C-0579(A), 278.C-5070(A) and from the Hubble Space Telescope under programme IDs SNAP-7387, GO-11164. Appendix A is available in electronic form at http://www.aanda.org

Three Investigations of Low Mass Stars in the Milky Way Using New Technology Surveys

NASA Astrophysics Data System (ADS)

Lurie, John C.

At least 80% of stars in the Milky Way have masses less than or equal to the Sun. These long lived stars are the most likely hosts of planets where complex life can develop. Although relatively stable on the timescale of billions of years, many low mass stars possess strong magnetic fields that are manifested in energetic surface activity, which may pose a hazard to both life and technology. Magnetic activity also influences the evolution of a low mass star through a feedback process that slows the rotation rate, which in turn tends to decrease the amount of activity. In this way, the rotation rate and activity level of a low mass star may provide an estimate of its age. Beyond their rotation-activity evolution as isolated objects, a small but important fraction of low mass stars have a close binary companion that influences the rotational and orbital properties of the system. Binary interaction can lead to phenomena such as supernovae, cataclysmic variables, and degenerate object mergers. From a larger perspective, low mass stars trace Galactic structure, and through their longevity serve as archives of the dynamical and chemical history of the Milky Way. Thus a full picture of low mass stars, and by extension the Milky Way, requires understanding their rotation and activity; their interaction in close binaries; and their spatial and kinematic distribution throughout the Galaxy. Historically, these topics have been approached from two separate but complementary modes of observation. Time series photometric surveys measure the stellar variability caused by rotation, activity, and binary interaction, while wide field surveys measure the brightnesses and colors of millions of stars to map their distribution in the Galaxy. The first generation of digital detectors and computing technology limited intensive time series surveys to a small number of stars, and limited wide field surveys to little if any variability information. Today those limitations are falling away

Movement simulation of the variable masses in the Gylden-Meshcherskii problem

DOE Office of Scientific and Technical Information (OSTI.GOV)

Starinova, Olga L.; Salmin, Vadim V.

The Gylden-Meshcherskii problem is used for various cases of dynamics of two points of the variable mass. For example, it describes of double star evolution due to mass loss at the photon expense and the corpuscular activity. Except, it is mathematical model for the movement of spacecraft with propulsion system. In the present work the mass variation laws, allowing a stationary form of the movement differential equations are considered. Movement simulation for all cases was conducted. The relative movement trajectories was constructed as for known Eddington-Jeans laws and for other mass variation laws.

ALMA Detection of Bipolar Outflows: Evidence for Low-mass Star Formation within 1 pc of Sgr A*

NASA Astrophysics Data System (ADS)

Yusef-Zadeh, F.; Wardle, M.; Kunneriath, D.; Royster, M.; Wootten, A.; Roberts, D. A.

2017-12-01

We report the discovery of 11 bipolar outflows within a projected distance of 1 pc from Sgr A* based on deep ALMA observations of 13CO, H30α, and SiO (5-4) lines with subarcsecond and ˜1.3 km s-1 resolutions. These unambiguous signatures of young protostars manifest as approaching and receding lobes of dense gas swept up by the jets created during the formation and early evolution of stars. The lobe masses and momentum transfer rates are consistent with young protostellar outflows found throughout the disk of the Galaxy. The mean dynamical age of the outflow population is estimated to be {6.5}-3.6+8.1× {10}3 years. The rate of star formation is ˜5 × 10-4 {M}⊙ yr-1 assuming a mean stellar mass of ˜0.3 {M}⊙ . This discovery provides evidence that star formation is taking place within clouds surprisingly close to Sgr A*, perhaps due to events that compress the host cloud, creating condensations with sufficient self-gravity to resist tidal disruption by Sgr A*. Low-mass star formation over the past few billion years at this level would contribute significantly to the stellar mass budget in the central few parsecs of the Galaxy. The presence of many dense clumps of molecular material within 1 pc of Sgr A* suggests that star formation could take place in the immediate vicinity of supermassive black holes in the nuclei of external galaxies.

Stability of libration points in the restricted four-body problem with variable mass

NASA Astrophysics Data System (ADS)

Mittal, Amit; Aggarwal, Rajiv; Suraj, Md. Sanam; Bisht, Virender Singh

2016-10-01

We have investigated the stability of the Lagrangian solutions for the restricted four-body problem with variable mass. It has been assumed that the three primaries with masses m1, m2 and m3 form an equilateral triangle, wherein m2=m3. According to Jeans' law (Astronomy and Cosmogony, Cambridge University Press, Cambridge, 1928), the infinitesimal body varies its mass m with time. The space-time transformations of Meshcherskii (Studies on the Mechanics of Bodies of Variable Mass, GITTL, Moscow, 1949) are used by taking the values of the parameters q=1/2, k=0, n=1. The equations of motion of the infinitesimal body with variable mass have been determined. The equations of motion of the current problem differ from the ones of the restricted four-body problem with constant mass. There exist eight libration points, out of which two are collinear with the primary m1 and the rest are non-collinear for a fixed value of parameters γ (m {at time} t/m {at initial time}, 0<γ≤1 ), α (the proportionality constant in Jeans' law (Astronomy and Cosmogony, Cambridge University Press, Cambridge, 1928), 0≤α≤2.2) and μ=0.019 (the mass parameter). All the libration points are found to be unstable. The zero velocity surfaces (ZVS) are also drawn and regions of motion are discussed.

A parsec-scale optical jet from a massive young star in the Large Magellanic Cloud.

PubMed

McLeod, Anna F; Reiter, Megan; Kuiper, Rolf; Klaassen, Pamela D; Evans, Christopher J

2018-02-15

Highly collimated parsec-scale jets, which are generally linked to the presence of an accretion disk, are commonly observed in low-mass young stellar objects. In the past two decades, a few of these jets have been directly (or indirectly) observed from higher-mass (larger than eight solar masses) young stellar objects, adding to the growing evidence that disk-mediated accretion also occurs in high-mass stars, the formation mechanism of which is still poorly understood. Of the observed jets from massive young stars, none is in the optical regime (massive young stars are typically highly obscured by their natal material), and none is found outside of the Milky Way. Here we report observations of HH 1177, an optical ionized jet that originates from a massive young stellar object located in the Large Magellanic Cloud. The jet is highly collimated over its entire measured length of at least ten parsecs and has a bipolar geometry. The presence of a jet indicates ongoing, disk-mediated accretion and, together with the high degree of collimation, implies that this system is probably formed through a scaled-up version of the formation mechanism of low-mass stars. We conclude that the physics that govern jet launching and collimation is independent of stellar mass.

A parsec-scale optical jet from a massive young star in the Large Magellanic Cloud

NASA Astrophysics Data System (ADS)

McLeod, Anna F.; Reiter, Megan; Kuiper, Rolf; Klaassen, Pamela D.; Evans, Christopher J.

2018-02-01

Highly collimated parsec-scale jets, which are generally linked to the presence of an accretion disk, are commonly observed in low-mass young stellar objects. In the past two decades, a few of these jets have been directly (or indirectly) observed from higher-mass (larger than eight solar masses) young stellar objects, adding to the growing evidence that disk-mediated accretion also occurs in high-mass stars, the formation mechanism of which is still poorly understood. Of the observed jets from massive young stars, none is in the optical regime (massive young stars are typically highly obscured by their natal material), and none is found outside of the Milky Way. Here we report observations of HH 1177, an optical ionized jet that originates from a massive young stellar object located in the Large Magellanic Cloud. The jet is highly collimated over its entire measured length of at least ten parsecs and has a bipolar geometry. The presence of a jet indicates ongoing, disk-mediated accretion and, together with the high degree of collimation, implies that this system is probably formed through a scaled-up version of the formation mechanism of low-mass stars. We conclude that the physics that govern jet launching and collimation is independent of stellar mass.

The Discovery of a Low-Mass Binary Companion to HD130948

NASA Astrophysics Data System (ADS)

Potter, D. E.; Cushing, M. C.; Neuhauser, R.

2003-10-01

We report the discovery of a low mass binary companion to the nearby (17.9 pc) main sequence star HD130948 (HR5534, HIP 72567) using the Hokupa'a adaptive optics instrument mounted on the Gemini North 8 meter telescope. Both companions have the same common proper motion as the primary star as seen over a 4 month baseline. The JHK' photometry of the companions, when placed on a near-IR color-magnitude diagram and compared with theoretical models places them at the bottom of the M-dwarf sequence. Preliminary near IR spectra have been obtained with SpeX mounted on the NASA IRTF 3 meter telescope are consistent with the photometric results and show carbon monoxide bandheads and water absorption features indicative of an early L-late M spectral type. The X-ray activity and Lithium abundance of the primary star indicate that the system is probably less than 1 Gyr old. Assuming a young age, these objects are less than 80 Mjupiter. With further astrometric observations carried out over an estimated orbital period of 10-20 years, a dynamical mass will be obtained.

Type VI collagen turnover-related peptides-novel serological biomarkers of muscle mass and anabolic response to loading in young men.

PubMed

Nedergaard, Anders; Sun, Shu; Karsdal, Morten A; Henriksen, Kim; Kjær, Michael; Lou, Yunyun; He, Yi; Zheng, Qinlong; Suetta, Charlotte

2013-12-01

Immobilization-induced loss of muscle mass is a complex phenomenon with several parallels to sarcopenic and cachectic muscle loss. Muscle is a large organ with a protein turnover that is orders of magnitude larger than most other tissues. Thus, we hypothesize that muscle loss and regain is reflected by peptide biomarkers derived from type VI collagen processing released in the circulation. In order to test this hypothesis, we set out to develop an ELISA assay against an type VI collagen N-terminal globular domain epitope (IC6) and measured the levels of IC6 and an MMP-generated degradation fragment of collagen 6, (C6M) in a human immobilization-remobilization study setup with young (n = 11) and old (n = 9) men. They were subjected to 2 weeks of unilateral lower limb immobilization followed by 4 weeks of remobilization including thrice weekly resistance training, using the contralateral leg as internal controls. Subjects were sampled for strength, quadriceps muscle volume and blood at baseline (PRE), post-immobilization (2W), and post-remobilization (4W). Blood were subsequently analyzed for levels of the C6M and IC6 biomarkers. We subsequently tested if there was any correlation between C6M, IC6, or the C6M/IC6 ratio and muscle mass or strength at baseline. We also tested whether there was any relation between these biomarkers and changes in muscle mass or strength with immobilization or remobilization. The model produced significant loss of muscle mass and strength in the immobilized leg. This loss was bigger in young subjects than in elderly, but whereas the young recovered almost fully, the elderly had limited regrowth of muscle. We found a significant correlation between IC6 and muscle mass at baseline in young subjects (R (2) = 0.6563, p = 0.0045), but none in the elderly. We also found a significant correlation between C6M measured at the 4W time point and the change in muscle mass during remobilization, again only manifesting in the young

Photometric Study of Fourteen Low-mass Binaries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Korda, D.; Zasche, P.; Wolf, M.

2017-07-01

New CCD photometric observations of fourteen short-period low-mass eclipsing binaries (LMBs) in the photometric filters I, R, and V were used for a light curve analysis. A discrepancy remains between observed radii and those derived from the theoretical modeling for LMBs, in general. Mass calibration of all observed LMBs was performed using only the photometric indices. The light curve modeling of these selected systems was completed, yielding the new derived masses and radii for both components. We compared these systems with the compilation of other known double-lined LMB systems with uncertainties of masses and radii less then 5%, which includesmore » 66 components of binaries where both spectroscopy and photometry were combined together. All of our systems are circular short-period binaries, and for some of them, the photospheric spots were also used. A purely photometric study of the light curves without spectroscopy seems unable to achieve high enough precision and accuracy in the masses and radii to act as meaningful test of the M–R relation for low-mass stars.« less

Mode Selection Techniques in Variable Mass Flexible Body Modeling

NASA Technical Reports Server (NTRS)

Quiocho, Leslie J.; Ghosh, Tushar K.; Frenkel, David; Huynh, An

2010-01-01

In developing a flexible body spacecraft simulation for the Launch Abort System of the Orion vehicle, when a rapid mass depletion takes place, the dynamics problem with time varying eigenmodes had to be addressed. Three different techniques were implemented, with different trade-offs made between performance and fidelity. A number of technical issues had to be solved in the process. This paper covers the background of the variable mass flexibility problem, the three approaches to simulating it, and the technical issues that were solved in formulating and implementing them.

High- and low-molecular-mass microbial surfactants.

PubMed

Rosenberg, E; Ron, E Z

1999-08-01

Microorganisms synthesize a wide variety of high- and low-molecular-mass bioemulsifiers. The low-molecular-mass bioemulsifiers are generally glycolipids, such as trehalose lipids, sophorolipids and rhamnolipids, or lipopeptides, such as surfactin, gramicidin S and polymyxin. The high-molecular-mass bioemulsifiers are amphipathic polysaccharides, proteins, lipopolysaccharides, lipoproteins or complex mixtures of these biopolymers. The low-molecular-mass bioemulsifiers lower surface and interfacial tensions, whereas the higher-molecular-mass bioemulsifiers are more effective at stabilizing oil-in-water emulsions. Three natural roles for bioemulsifiers have been proposed: (i) increasing the surface area of hydrophobic water-insoluble growth substrates; (ii) increasing the bioavailability of hydrophobic substrates by increasing their apparent solubility or desorbing them from surfaces; (iii) regulating the attachment and detachment of microorganisms to and from surfaces. Bioemulsifiers have several important advantages over chemical surfactants, which should allow them to become prominent in industrial and environmental applications. The potential commercial applications of bioemulsifiers include bioremediation of oil-polluted soil and water, enhanced oil recovery, replacement of chlorinated solvents used in cleaning-up oil-contaminated pipes, vessels and machinery, use in the detergent industry, formulations of herbicides and pesticides and formation of stable oil-in-water emulsions for the food and cosmetic industries.

A Search for Low Mass Stars and Substellar Companions and A Study of Circumbinary Gas and Dust Disks

NASA Astrophysics Data System (ADS)

Rodriguez, David R.

2011-01-01

We have searched for nearby low-mass stars and brown dwarfs and have studied the planet-forming environment of binary stars. We have carried out a search for young, low-mass stars in nearby stellar associations using X-ray and UV source catalogs. We discovered a new technique to identify 10-100 Myr-old low-mass stars within 100 pc of the Earth using GALEX-optical/near-IR data. We present candidate young stars found by applying this new method in the 10 Myr old TW Hydrae and Scorpius-Centaurus associations. In addition, we have searched for the coolest brown dwarf class: Y-dwarfs, expected to appear at temperatures <500 K. Using wide-field near infrared imaging with ground (CTIO, Palomar, KPNO) and space (Spitzer, AKARI) observatories, we have looked for companions to nearby, old (2 Gyr or older), high proper motion white dwarfs. We present results for Southern Hemisphere white dwarfs. Additionally, we have characterized how likely planet formation occurs in binary star systems. While 20% of planets have been discovered around one member of a binary system, these binaries have semi-major axes larger than 20 AU. We have performed an AO and spectroscopic search for binary stars among a sample of known debris disk stars, which allows us to indirectly study planet formation and evolution in binary systems. As a case study, we examined the gas and dust present in the circumbinary disk around V4046 Sagittarii, a 2.4-day spectroscopic binary. Our results demonstrate it is unlikely that planets can form in binaries with stellar semi-major axes of 10s of AU. This research has been funded by a NASA ADA grant to UCLA and RIT.

A Mass Circulation View of the Low Frequency Nature of the Stratospheric Northern Annular Mode

NASA Astrophysics Data System (ADS)

Yu, Y.; Cai, M.

2016-12-01

We consider three indices to measure polar stratospheric mass and stratospheric meridional mass circulation variability: anomalies of (i) total mass in the polar stratospheric cap (60-90°N, above the isentropic surface 400 K, PSM), (ii) total adiabatic mass transport across 60°N into the polar stratosphere cap (AMT), (iii) and total diabatic mass transport across 400 K into the polar stratosphere (DMT). It is confirmed that the negative stratospheric Northern Annular Mode (NAM) and normalized PSM indices have a nearly indistinguishable temporal evolution and both indices have the same red-noise-like spectrum with the de-correlation timescale of 4 weeks. In this sense, these two indices are synonymous with each other. This enables us to examine the low-frequency nature of the PSM (or NAM) index in the framework of the mass conservation, namely, dPSM/dt=AMT+DMT . Results indicate that the DMT index tends to be negatively correlated with the PSM index and also has a red-noise-like spectrum with the de-correlation timescale of 3-4 weeks. The AMT index, however, has a large positive correlation with the tendency of the PSM rather than the PSM itself. The temporal variability of the AMT has otherwise white-noise-like spectrum except with a pronounced peak at the 2-week timescale. Therefore, the conservation equation of the PSM behaves like a linear stochastic differential equation with the DMT serving as the thermal damping term and the AMT as the high-frequency white noise source term. It follows that the low-frequency nature of the stratospheric NAM (or PSM) index can be viewed as the red-noise response to a white noise in a fluctuation-dissipation system.

Parental Perceptions of Life Context Variables for Involvement in Their Young Children's Education

ERIC Educational Resources Information Center

Tekin, Ali Kemal

2016-01-01

The purpose of this study was to discover Turkish parents' perceptions of life context variables, including personal knowledge and skills and personal time and energy for involvement activities in their young children's education. The scales used in this study were based on parents' self-report, and included: (1) Parental Perceptions of Personal…

VLA Observations of the Disk around the Young Brown Dwarf 2MASS J044427+2512

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ricci, L.; Rome, H.; Pinilla, P.

We present multi-wavelength radio observations obtained with the VLA of the protoplanetary disk surrounding the young brown dwarf 2MASS J04442713+2512164 (2M0444) in the Taurus star-forming region. 2M0444 is the brightest known brown dwarf disk at millimeter wavelengths, making this an ideal target to probe radio emission from a young brown dwarf. Thermal emission from dust in the disk is detected at 6.8 and 9.1 mm, whereas the 1.36 cm measured flux is dominated by ionized gas emission. We combine these data with previous observations at shorter sub-mm and mm wavelengths to test the predictions of dust evolution models in gas-richmore » disks after adapting their parameters to the case of 2M0444. These models show that the radial drift mechanism affecting solids in a gaseous environment has to be either completely made inefficient, or significantly slowed down by very strong gas pressure bumps in order to explain the presence of mm/cm-sized grains in the outer regions of the 2M0444 disk. We also discuss the possible mechanisms for the origin of the ionized gas emission detected at 1.36 cm. The inferred radio luminosity for this emission is in line with the relation between radio and bolometric luminosity valid for for more massive and luminous young stellar objects, and extrapolated down to the very low luminosity of the 2M0444 brown dwarf.« less

Ginga observations of dipping low mass X ray binaries

NASA Technical Reports Server (NTRS)

Smale, Alan P.; Mukai, Koji; Williams, O. Rees; Jones, Mark H.; Parmar, Arvind N.; Corbet, Robin H. D.

1989-01-01

Ginga observations of several low mass X ray binaries displaying pronounced dips of variable depth and duration in their X ray light curves are analyzed. The periodic occultation of the central X ray source by azimuthal accretion disk structure is considered. A series of spectra selected by intensity from the dip data from XB1916-053, are presented. The effects of a rapidly changing column density upon the spectral fitting results are modeled. EXO0748-676 was observed in March 1989 for three days. The source was found to be in a bright state with a 1 to 20 keV flux of 8.8 x 10 (exp -10) erg/sqcms. The data include two eclipses, observed with high time resolution.

Gravitational lensing by a smoothly variable surface mass density

NASA Technical Reports Server (NTRS)

Paczynski, Bohdan; Wambsganss, Joachim

1989-01-01

The statistical properties of gravitational lensing due to smooth but nonuniform distributions of matter are considered. It is found that a majority of triple images had a parity characteristic for 'shear-induced' lensing. Almost all cases of triple or multiple imaging were associated with large surface density enhancements, and lensing objects were present between the images. Thus, the observed gravitational lens candidates for which no lensing object has been detected between the images are unlikely to be a result of asymmetric distribution of mass external to the image circle. In a model with smoothly variable surface mass density, moderately and highly amplified images tended to be single rather than multiple. An opposite trend was found in models which had singularities in the surface mass distribution.

The influence of divided attention on walking turns: Effects on gait control in young adults with and without a history of low back pain.

PubMed

Smith, Jo Armour; Gordon, James; Kulig, Kornelia

2017-10-01

The cognitive control of gait is altered in individuals with low back pain, but it is unclear if this alteration persists between painful episodes. Locomotor perturbations such as walking turns may provide a sensitive measure of gait adaptation during divided attention in young adults. The purpose of this study was to investigate changes in gait during turns performed with divided attention, and to compare healthy young adults with asymptomatic individuals who have a history of recurrent low back pain (rLBP). Twenty-eight participants performed 90° ipsilateral walking turns at a controlled speed of 1.5m/s. During the divided attention condition they concurrently performed a verbal 2-back task. Step length and width, trunk-pelvis and hip excursion, inter-segmental coordination and stride-to-stride variability were quantified using motion capture. Mixed-model ANOVA were used to examine the effect of divided attention and group, and interaction effects on the selected variables. Step length variability decreased significantly with divided attention in the healthy group but not in the rLBP group (post-hoc p=0.024). Inter-segmental coordination variability was significantly decreased during divided attention (main effect of condition p <0.000). There were small but significant reductions in hip axial and sagittal motion across groups (main effect of condition p=0.044 and p=0.040 respectively), and a trend toward increased frontal motion in the rLBP group only (post-hoc p=0.048). These findings suggest that the ability to switch attentional resources during gait is altered in young adults with a history of rLBP, even between symptomatic episodes. Copyright © 2017 Elsevier B.V. All rights reserved.

Ages of Young Star Clusters, Massive Blue Stragglers, and the Upper Mass Limit of Stars: Analyzing Age-dependent Stellar Mass Functions

NASA Astrophysics Data System (ADS)

Schneider, F. R. N.; Izzard, R. G.; de Mink, S. E.; Langer, N.; Stolte, A.; de Koter, A.; Gvaramadze, V. V.; Hußmann, B.; Liermann, A.; Sana, H.

2014-01-01

Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. The latter aspect is important for populations of massive stars as more than 70% of all O stars are expected to interact with a binary companion during their lifetime. We show that such mass changes leave characteristic signatures in stellar mass functions of young star clusters that can be used to infer their ages and to identify products of binary evolution. We model the observed present-day mass functions of the young Galactic Arches and Quintuplet star clusters using our rapid binary evolution code. We find that the shaping of the mass function by stellar wind mass loss allows us to determine the cluster ages as 3.5 ± 0.7 Myr and 4.8 ± 1.1 Myr, respectively. Exploiting the effects of binary mass exchange on the cluster mass function, we find that the most massive stars in both clusters are rejuvenated products of binary mass transfer, i.e., the massive counterpart of classical blue straggler stars. This resolves the problem of an apparent age spread among the most luminous stars exceeding the expected duration of star formation in these clusters. We perform Monte Carlo simulations to probe stochastic sampling, which support the idea of the most massive stars being rejuvenated binary products. We find that the most massive star is expected to be a binary product after 1.0 ± 0.7 Myr in Arches and after 1.7 ± 1.0 Myr in Quintuplet. Today, the most massive 9 ± 3 stars in Arches and 8 ± 3 in Quintuplet are expected to be such objects. Our findings have strong implications for the stellar upper mass limit and solve the discrepancy between the claimed 150 M ⊙ limit and observations of four stars with initial masses of 165-320 M ⊙ in R136 and of supernova 2007bi, which is thought to be a pair-instability supernova from an initial 250 M ⊙ star. Using the stellar population of R136, we revise the upper mass limit to values in the range 200-500 M ⊙.

Ages of young star clusters, massive blue stragglers, and the upper mass limit of stars: Analyzing age-dependent stellar mass functions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schneider, F. R. N.; Izzard, R. G.; Langer, N.

2014-01-10

Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. The latter aspect is important for populations of massive stars as more than 70% of all O stars are expected to interact with a binary companion during their lifetime. We show that such mass changes leave characteristic signatures in stellar mass functions of young star clusters that can be used to infer their ages and to identify products of binary evolution. We model the observed present-day mass functions of the young Galactic Arches and Quintuplet star clusters using our rapid binary evolution code. Wemore » find that the shaping of the mass function by stellar wind mass loss allows us to determine the cluster ages as 3.5 ± 0.7 Myr and 4.8 ± 1.1 Myr, respectively. Exploiting the effects of binary mass exchange on the cluster mass function, we find that the most massive stars in both clusters are rejuvenated products of binary mass transfer, i.e., the massive counterpart of classical blue straggler stars. This resolves the problem of an apparent age spread among the most luminous stars exceeding the expected duration of star formation in these clusters. We perform Monte Carlo simulations to probe stochastic sampling, which support the idea of the most massive stars being rejuvenated binary products. We find that the most massive star is expected to be a binary product after 1.0 ± 0.7 Myr in Arches and after 1.7 ± 1.0 Myr in Quintuplet. Today, the most massive 9 ± 3 stars in Arches and 8 ± 3 in Quintuplet are expected to be such objects. Our findings have strong implications for the stellar upper mass limit and solve the discrepancy between the claimed 150 M {sub ☉} limit and observations of four stars with initial masses of 165-320 M {sub ☉} in R136 and of supernova 2007bi, which is thought to be a pair-instability supernova from an initial 250 M {sub ☉} star. Using the stellar population of R136, we revise the upper mass limit to values in

Dynamic characteristics of a two-stage variable-mass flexible missile with internal flow

NASA Technical Reports Server (NTRS)

Meirovitch, L.; Bankovskis, J.

1972-01-01

A general formulation of the dynamical problems associated with powered flight of a two stage flexible, variable-mass missile with internal flow, discrete masses, and aerodynamic forces is presented. The formulation comprises six ordinary differential equations for the rigid body motion, 3n ordinary differential equations for the n discrete masses and three partial differential equations with the appropriate boundary conditions for the elastic motion. This set of equations is modified to represent a single stage flexible, variable-mass missile with internal flow and aerodynamic forces. The rigid-body motion consists then of three translations and three rotations, whereas the elastic motion is defined by one longitudinal and two flexural displacements, the latter about two orthogonal transverse axes. The differential equations are nonlinear and, in addition, they possess time-dependent coefficients due to the mass variation.

Low Mass X-ray Binary 4U1705-44 Exiting an Extended High X-ray State

NASA Astrophysics Data System (ADS)

Phillipson, Rebecca; Boyd, Patricia T.; Smale, Alan P.

2017-09-01

The neutron-star low-mass X-ray binary 4U1705-44, which exhibited high amplitude long-term X-ray variability on the order of hundreds of days during the 16-year continuous monitoring by the RXTE ASM (1995-2012), entered an anomalously long high state in July 2012 as observed by MAXI (2009-present).

EPISODIC ACCRETION AT EARLY STAGES OF EVOLUTION OF LOW-MASS STARS AND BROWN DWARFS: A SOLUTION FOR THE OBSERVED LUMINOSITY SPREAD IN H-R DIAGRAMS?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baraffe, I.; Chabrier, G.; Gallardo, J.

2009-09-01

We present evolutionary models for young low-mass stars and brown dwarfs taking into account episodic phases of accretion at early stages of the evolution, a scenario supported by recent large surveys of embedded protostars. An evolution including short episodes of vigorous accretion followed by longer quiescent phases can explain the observed luminosity spread in H-R diagrams of star-forming regions at ages of a few Myr, for objects ranging from a few Jupiter masses to a few tenths of a solar mass. The gravitational contraction of these accreting objects strongly departs from the standard Hayashi track at constant T{sub eff}. Themore » best agreement with the observed luminosity scatter is obtained if most of the accretion shock energy is radiated away. The obtained luminosity spread at 1 Myr in the H-R diagram is equivalent to what can be misinterpreted as an {approx}10 Myr age spread for non-accreting objects. We also predict a significant spread in radius at a given T{sub eff}, as suggested by recent observations. These calculations bear important consequences for our understanding of star formation and early stages of evolution and on the determination of the initial mass function for young ({<=} a few Myr) clusters. Our results also show that the concept of a stellar birthline for low-mass objects has no valid support.« less

A Portrait of Low-Income Young Adults in Education. Portraits

ERIC Educational Resources Information Center

Institute for Higher Education Policy, 2010

2010-01-01

This brief takes a broad look at low-income young adults in an effort to contribute to the national discussion on improving degree completion by increasing participation among all disadvantaged populations--especially those who attempt to succeed in postsecondary settings under financial stress. Understanding the linkages between low-income young…

The Search for Young Planetary Systems And the Evolution of Young Stars

NASA Technical Reports Server (NTRS)

Beichman, Charles A.; Boden, Andrew; Ghez, Andrea; Hartman, Lee W.; Hillenbrand, Lynn; Lunine, Jonathan I.; Simon, Michael J.; Stauffer, John R.; Velusamy, Thangasamy

2004-01-01

and migrate from their place of birth, and about their survival rate. With these data in hand, we will provide data, for the first time, on such important questions as: What processes affect the formation and dynamical evolution of planets? When and where do planets form? What is initial mass distribution of planetary systems around young stars? How might planets be destroyed? What is the origin of the eccentricity of planetary orbits? What is the origin of the apparent dearth of companion objects between planets and brown dwarfs seen in mature stars? The observational strategy is a compromise between the desire to extend the planetary mass function as low as possible and the essential need to build up sufficient statistics on planetary occurrence. About half of the sample will be used to address the "where" and "when" of planet formation. We will study classical T Tauri stars (cTTs) which have massive accretion disks and post- accretion, weak-lined T Tauri stars (wTTs). Preliminary estimates suggest the sample will consist of approx. 30% cTTs and approx. 70% wTTs, driven in part by the difficulty of making accurate astrometric measurements toward objects with strong variability or prominent disks.

Trends and interannual variability of mass and steric sea level in the Tropical Asian Seas

NASA Astrophysics Data System (ADS)

Kleinherenbrink, Marcel; Riva, Riccardo; Frederikse, Thomas; Merrifield, Mark; Wada, Yoshihide

2017-08-01

The mass and steric components of sea level changes have been separated in the Tropical Asian Seas (TAS) using a statistically optimal combination of Jason satellite altimetry, GRACE satellite gravimetry, and ocean reanalyses. Using observational uncertainties, statistically optimally weighted time series for both components have been obtained in four regions within the TAS over the period January 2005 to December 2012. The mass and steric sea level variability is regressed with the first two principal components (PC1&2) of Pacific equatorial wind stress and the Dipole Mode Index (DMI). Sea level in the South China Sea is not affected by any of the indices. Steric variability in the TAS is largest in the deep Banda and Celebes seas and is affected by both PCs and the DMI. Mass variability is largest on the continental shelves, which is primarily controlled by PC1. We argue that a water flux from the Western Tropical Pacific Ocean is the cause for mass variability in the TAS. The steric trends are about 2 mm yr-1 larger than the mass trends in the TAS. A significant part of the mass trend can be explained by the aforementioned indices and the nodal cycle. Trends obtained from fingerprints of mass redistribution are statistically equal to mass trends after subtracting the nodal cycle and the indices. Ultimately, the effect of omitting the TAS in global sea level budgets is estimated to be 0.3 mm yr-1.

Variable stars around selected open clusters in the VVV area: Young Stellar Objects

NASA Astrophysics Data System (ADS)

Medina, Nicolas; Borissova, Jura; Bayo, Amelia; Kurtev, Radostin; Lucas, Philip

2017-09-01

Time-varying phenomena are one of the most substantial sources of astrophysical information, and led to many fundamental discoveries in modern astronomy. We have developed an automated tool to search and analyze variable sources in the near infrared Ks band, using the data from the Vista Variables in the Vía Láctea (VVV) ESO Public Survey ([5, 8]). One of our main goals is to investigate the Young Stellar Objects (YSOs) in the Galactic star forming regions, looking for: •Variability. •New pre-main sequence star clusters. Here we present the newly discovered YSOs within some selected stellar clusters in our Galaxy.

Effect of whole-body vibration on center-of-mass movement during standing in children and young adults.

PubMed

Liang, Huaqing; Beerse, Matthew; Ke, Xiang; Wu, Jianhua

2017-05-01

Whole body vibration (WBV) can affect postural control and muscular activation. The purpose of this study was to investigate the center-of-mass (COM) movement of children and young adults before, during, immediately after, and 5min after 40-s WBV in quiet standing. Fourteen young adults (mean age 24.5 years) and fourteen children (mean age 8.1 years) participated in the study. A full-body 35-marker set was placed on the participants and used to calculate COM. Forty-second standing trials were collected before, during, immediately after, and 5min after WBV with an frequency of 28Hz and an amplitude of <1mm. Two visual conditions were provided: eyes-open (EO) and eyes-closed (EC). COM variables included time-domain measures (average velocity, range, sway area and fractal dimension), frequency-domain measures (total power and median frequency), and detrended fluctuation analysis (DFA) scaling exponent in both anterior-posterior (AP) and medial-lateral (ML) directions. Results show that during WBV both children and adults increased average velocity and median frequency, but decreased range and the DFA scaling exponent. Immediately after WBV both groups increased the range, but showed pre-vibration values for most of the COM variables. Comparing to adults, children displayed a higher COM velocity, range, fractal dimension, and total power, but a lower DFA scaling exponent at all phases. The results suggest that both children and adults can quickly adapt their postural control system to WBV and maintain balance during and after vibration. Children display some adult-like postural control during and after WBV; however, their postural development continues into adolescence. Published by Elsevier B.V.

Newtonian Version of the Variable Mass Theory of Gravity

NASA Astrophysics Data System (ADS)

Carvalho, J. C.; Lima, J. A. S.

1990-11-01

RESUMEN. Se presenta una versi6n Newtoniana de los modelos cosmol6gicos espacialmente e isotr6picos con masa variable. La influencia de la variaci6n de masa en la evoluci6n de la funci6n de escala est establecida para el caso de un Universo lieno de polvo bajo Ia suposici6n de que esta variaci6n es un efecto estrictamente cosmol6jico. Se muestra que el hiperb6lico, parab6lico 0 el#ptico dcl movimiento de puede ser modificado a lo larjo de la expansi6n. ABSTRACT. This paper presents a Newtonian version of the spatially homojeneous and isotropic cosmolojical models with variable mass. The influence of the mass variation on the evolution of the scale function is established for the case of a dust-filled Universe under the assumption that this variation is a strict cosmolojical effect. It is shown that the hyperbolic, parabolic or elliptic character of the fluid motion can be modified alonj the expansion. Keq : COSMOLOGY

Extreme Variables in Star Forming Regions

NASA Astrophysics Data System (ADS)

Contreras Peña, Carlos Eduardo

2015-01-01

The notion that low- to intermediate-mass young stellar objects (YSOs) gain mass at a constant rate during the early stages of their evolution appears to be challenged by observations of YSOs suffering sudden increases of the rate at which they gain mass from their circumstellar discs. Also, this idea that stars spend most of their lifetime with a low accretion rate and gain most of their final mass during short-lived episodes of high accretion bursts, helps to solve some long-standing problems in stellar evolution. The original classification of eruptive variables divides them in two separate subclasses known as FU Orionis stars (FUors) and EX Lupi stars (EXors). In this classical view FUors are at an early evolutionary stage and are still gaining mass from their parent envelopes, whilst EXors are thought to be older objects only surrounded by an accretion disc. The problem with this classical view is that it excludes younger protostars which have higher accretion rates but are too deeply embedded in circumstellar matter to be observed at optical wavelengths. Optically invisible protostars have been observed to display large variability in the near-infrared. These and some recent discoveries of new eruptive variables, show characteristics that can be attributed to both of the optically-defined subclasses of eruptive variables. The new objects have been proposed to be part of a new class of eruptive variables. However, a more accepted scenario is that in fact the original classes only represent two extremes of the same phenomena. In this sense eruptive variability could be explained as arising from one physical mechanism, i.e. unsteady accretion, where a variation in the parameters of such mechanism can cause the different characteristics observed in the members of this class. With the aim of studying the incidence of episodic accretion among young stellar objects, and to characterize the nature of these eruptive variables we searched for high amplitude variability

Comparative glacio-climatological analysis of mass balance variability along the geographical margin of Europe

NASA Astrophysics Data System (ADS)

Lehoczky, Annamária; Kern, Zoltán; Pongrácz, Rita

2014-05-01

Glacio-climatological studies recognise glacier mass balance changes as high-confident climate indicators. The climatic sensitivity of a glacier does not simply depend on regional climate variability but also influenced via large- and mesoscale atmospheric circulation patterns. This study focuses on recent changes in the mass balance using records from three border regions of Europe, and investigates the relationships between the seasonal mass balance components, regional climatic conditions, and distant atmospheric forcing. Since glaciers in different macro-climatological conditions (i.e., mid-latitudes or high-latitudes, dry-continental or maritime regions) may present strongly diverse mass balance characteristics, the three analysed regions were selected from different glacierised macroregions (using the database of the World Glacier Monitoring Service). These regions belong to the Caucasus Mountains (Central Europe macroregion), the Polar Ural (Northern Asia macroregion), and Svalbard (Arctic Islands macroregion). The analysis focuses on winter, summer, and annual mass balance series of eight glaciers. The climatic variables (atmospheric pressure, air temperature, precipitation) and indices of teleconnection patterns (e.g., North Atlantic Oscillation, Pacific Decadal Oscillation) are used from the gridded databases of the University of East Anglia, Climatic Research Unit and the National Oceanic and Atmospheric Administration, National Center for Environmental Prediction. However, the period and length of available mass balance data in the selected regions vary greatly (the first full record is in 1958, Polar Ural; the last is in 2010, Caucasus Mountains), a comparative analysis can be carried out for the period of 1968-1981. Since glaciers from different regions respond to large- and mesoscale climatic forcings differently, and because the mass balance of glaciers within a region often co-vary, our specific objectives are (i) to examine the variability and the

Low-Income Mothers' Food Practices with Young Children: A Qualitative Longitudinal Study

ERIC Educational Resources Information Center

Harden, Jeni; Dickson, Adele

2015-01-01

Objective: Young children living in socioeconomically deprived areas of Scotland have an increased risk of becoming overweight or obese. To enhance understanding of the wider contexts within which family food practices are developed, this study examined the experiences of low-income mothers with young children. Design: Qualitative longitudinal…

Cardiometabolic Risks and Severity of Obesity in Children and Young Adults.

PubMed

Skinner, Asheley C; Perrin, Eliana M; Moss, Leslie A; Skelton, Joseph A

2015-10-01

The prevalence of severe obesity among children and young adults has increased over the past decade. Although the prevalence of cardiometabolic risk factors is relatively low among children and young adults who are overweight or obese, those with more severe forms of obesity may be at greater risk. We performed a cross-sectional analysis of data from overweight or obese children and young adults 3 to 19 years of age who were included in the National Health and Nutrition Examination Survey from 1999 through 2012 to assess the prevalence of multiple cardiometabolic risk factors according to the severity of obesity. Weight status was classified on the basis of measured height and weight. We used standard definitions of abnormal values for total cholesterol, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein cholesterol, triglycerides, blood pressure, glycated hemoglobin, and fasting glucose and report the prevalence of abnormal values in children and young adults according to weight status. Among 8579 children and young adults with a body-mass index at the 85th percentile or higher (according to the Centers for Disease Control and Prevention growth charts), 46.9% were overweight, 36.4% had class I obesity, 11.9% had class II obesity, and 4.8% had class III obesity. Mean values for some, but not all, cardiometabolic variables were higher with greater severity of obesity in both male and female participants, and the values were higher in male participants than in female participants; for HDL cholesterol, the mean values were lower with greater severity of obesity. Multivariable models that controlled for age, race or ethnic group, and sex showed that the greater the severity of obesity, the higher the risks of a low HDL cholesterol level, high systolic and diastolic blood pressures, and high triglyceride and glycated hemoglobin levels. Severe obesity in children and young adults was associated with an increased prevalence of cardiometabolic risk factors

Changes in triglyceride levels and risk for coronary heart disease in young men.

PubMed

Tirosh, Amir; Rudich, Assaf; Shochat, Tzippora; Tekes-Manova, Dorit; Israeli, Eran; Henkin, Yaakov; Kochba, Ilan; Shai, Iris

2007-09-18

Current triglyceride levels might be only a weak predictor of risk for coronary heart disease (CHD). To assess the association between changes over time in fasting triglyceride levels and CHD risk in young adults. Follow-up study over 5.5 years after 2 measurements of fasting triglycerides 5 years apart. The Staff Periodic Examination Center of the Israel Defense Forces, Zrifin, Israel. 13,953 apparently healthy, untreated, young men (age 26 to 45 years) with triglyceride levels less than 3.39 mmol/L (<300 mg/dL). Two triglyceride measurements (at enrollment [time 1] and 5 years later [time 2]), lifestyle variables, and incident cases of angiography-proven CHD. Within 5.5 years, 158 new cases of CHD were identified. The multivariate model was adjusted for age; family history; fasting glucose; high-density lipoprotein cholesterol; blood pressure; body mass index; and changes between time 1 and time 2 in body mass index, physical activity, smoking status, and habit of eating breakfast. Investigators categorized triglyceride levels according to low, intermediate, and high tertiles (as measured at time 1 and time 2 [expressed as tertile at time 1/tertile at time 2]). The risk for CHD in men with high-tertile triglyceride levels at time 1 changed depending on the tertile at time 2 (hazard ratios, 8.23 [95% CI, 2.50 to 27.13] for high/high, 6.84 [CI, 1.95 to 23.98] for high/intermediate, and 4.90 [CI, 1.01 to 24.55] for high/low, compared with the stable low/low group). The risk for CHD in men with low-tertile levels at time 1 also changed depending on the tertile at time 2 (hazard ratios, 3.81 [CI, 0.96 to 15.31] for low/intermediate and 6.76 [CI, 1.34 to 33.92] for low/high, compared with the stable low/low group). Participants were healthy and had a low incidence rate of CHD. The study was observational. Two triglyceride measurements obtained 5 years apart may assist in assessing CHD risk in young men. A decrease in initially elevated triglyceride levels is associated

The low-mass star and disk populations in NGC 6611

NASA Astrophysics Data System (ADS)

Oliveira, Joana

2005-07-01

The aim of our observational program is to find empirical answers to two major questions. Do regions of high-mass star formation also produce lots of solar- and low-mass stars, i.e. is the low-mass IMF unaffected by high-mass siblings? Can low-mass stars in hostile environments retain circumstellar disks? We present results of our survey of NGC 6611, a massive cluster with an age of approximately 2 Myr which is currently ionizing the Eagle nebula. This cluster contains a dozen O-stars that emit 10 times more ionizing radiation than the Trapezium, providing a challenging environment for their lower-mass siblings. Our dataset consists of wide field optical and near infrared imaging, intermediate resolution spectroscopy (ESO-VLT) and deep L-band photometry. We have photometrically selected solar- and low-mass stars, placed them on the HR diagram and determined the IMF over an area sufficient to deal with mass segregation. We show that the IMF in NGC6611 is similar to that of the Orion Nebula Cluster down to 0.5Msun. Using K-L indices we search for colour excesses that betray the presence of circumstellar material and study what fraction of solar-mass stars still possess disks as a function of age and proximity to the massive stars. By comparing the disk frequency in NGC6611 with similarly aged but quieter regions, we find no evidence that the harsher environment of NGC6611 significantly hastens disk dissipation. Apparently the massive stars in NGC6611 have no global effect on the probability of low-mass star formation or disk retention. We have an approved HST program that will allows us to investigate the very low-mass and brown dwarf populations in NGC6611. And we complement our IR imaging with Spitzer/ORAC data, extending the area of our ground-based survey.

Optical and Near-infrared Spectra of σ Orionis Isolated Planetary-mass Objects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zapatero Osorio, M. R.; Béjar, V. J. S.; Ramírez, K. Peña, E-mail: mosorio@cab.inta-csic.es, E-mail: vbejar@iac.es, E-mail: karla.pena@uantof.cl

We have obtained low-resolution optical (0.7–0.98 μ m) and near-infrared (1.11–1.34 μ m and 0.8–2.5 μ m) spectra of 12 isolated planetary-mass candidates ( J = 18.2–19.9 mag) of the 3 Myr σ Orionis star cluster with the aim of determining the spectroscopic properties of very young, substellar dwarfs and assembling a complete cluster mass function. We have classified our targets by visual comparison with high- and low-gravity standards and by measuring newly defined spectroscopic indices. We derived L0–L4.5 and M9–L2.5 using high- and low-gravity standards, respectively. Our targets reveal clear signposts of youth, thus corroborating their cluster membership andmore » planetary masses (6–13 M {sub Jup}). These observations complete the σ Orionis mass function by spectroscopically confirming the planetary-mass domain to a confidence level of ∼75%. The comparison of our spectra with BT-Settl solar metallicity model atmospheres yields a temperature scale of 2350–1800 K and a low surface gravity of log g ≈ 4.0 [cm s{sup −2}], as would be expected for young planetary-mass objects. We discuss the properties of the cluster’s least-massive population as a function of spectral type. We have also obtained the first optical spectrum of S Ori 70, a T dwarf in the direction of σ Orionis. Our data provide reference optical and near-infrared spectra of very young L dwarfs and a mass function that may be used as templates for future studies of low-mass substellar objects and exoplanets. The extrapolation of the σ Orionis mass function to the solar neighborhood may indicate that isolated planetary-mass objects with temperatures of ∼200–300 K and masses in the interval 6–13 M {sub Jup} may be as numerous as very low-mass stars.« less

The beliefs which motivate young male and female drivers to speed: a comparison of low and high intenders.

PubMed

Horvath, C; Lewis, I; Watson, B

2012-03-01

In Australia, young drivers aged 17-24 years, and particularly males, have the highest risk of being involved in a fatal crash. Investigation of young drivers' beliefs allows for a greater understanding of their involvement in risky behaviours, such as speeding, as beliefs are associated with intentions, the antecedent to behaviour. The theory of planned behaviour (TPB) was used to conceptualise beliefs using a scenario based questionnaire distributed to licenced drivers (N=398). The questionnaire measured individual's beliefs and intentions to speed in a particular situation. Consistent with a TPB-based approach, the beliefs of those with low intentions to speed ('low intenders') were compared with the beliefs of those with high intentions ('high intenders') with such comparisons conducted separately for males and females. Overall, significant differences in the beliefs held by low and high intenders and for both females and males were found. Specifically, for females, it was found that high intenders were significantly more likely to perceive advantages of speeding, less likely to perceive disadvantages, and more likely to be encouraged to speed on familiar and inappropriately signed roads than female low intenders. Females, however, did not differ in their perceptions of support from friends, with all females reporting some level of disapproval from most friends and all females (i.e., low and high intenders) reporting approval to speed from their male friends. The results for males revealed that high intenders were significantly more likely to speed on familiar and inappropriately signed roads as well as having greater perceptions of support from all friends, except from those friends with whom they worked. Low and high intending males did not differ in their perceptions of the advantages and disadvantages of speeding, with the exception of feelings of excitement whereby high intenders reported speeding to be more exciting than low intenders. The findings are

Dynamic Responses of Flexible Cylinders with Low Mass Ratio

NASA Astrophysics Data System (ADS)

Olaoye, Abiodun; Wang, Zhicheng; Triantafyllou, Michael

2017-11-01

Flexible cylinders with low mass ratios such as composite risers are attractive in the offshore industry because they require lower top tension and are less likely to buckle under self-weight compared to steel risers. However, their relatively low stiffness characteristics make them more vulnerable to vortex induced vibrations. Additionally, numerical investigation of the dynamic responses of such structures based on realistic conditions is limited by high Reynolds number, complex sheared flow profile, large aspect ratio and low mass ratio challenges. In the framework of Fourier spectral/hp element method, the current technique employs entropy-viscosity method (EVM) based large-eddy simulation approach for flow solver and fictitious added mass method for structure solver. The combination of both methods can handle fluid-structure interaction problems at high Reynolds number with low mass ratio. A validation of the numerical approach is provided by comparison with experiments.

Obesity in young Dutch adults: II, daily life-style and body mass index.

PubMed

Baecke, J A; Burema, J; Frijters, J E; Hautvast, J G; van der Wiel-Wetzels, W A

1983-01-01

The relationships between aspects of daily life-style and age, level of education, and body mass index (BMI; weight/height) were studied in young adult males (n = 1765) and females (n = 2092) in three age groups (19-21, 24-26 and 29-31 yr) in a Dutch population. By means of principal-components analysis five conceptually meaningful factors could be distinguished within the aspects of daily life-style which were considered. These factors were interpreted as constructs of: (1) slimming behaviour; (2) behaviour characterized by the consumption of coffee and alcohol, smoking habits and the number of hours sleep per night (CASS behaviour); (3) eating sweet and savoury snacks between meals; (4) health-conscious behaviour; and (5) physical activity. After adjustments were made for age and level of education, multiple regression analysis showed that slimming behaviour was positively related to BMI in both sexes, CASS behaviour was positively related to BMI in males, and health-conscious behaviour was inversely related to BMI in both sexes. An observed positive relationship between BMI and occupational physical activity in males could be explained by a confounding effect of socio-economic status. The observed weak positive relationship between number of hours active sport per month and BMI in males is possibly due to a difference in lean body mass. The consumption of sweet and savoury snacks was not related to BMI in either sex. These findings suggest that the daily life-style variables should be interpreted as indicators of more general types of behaviour, some of which may be important determinants of obesity.

Sugars consumption in a low-income sample of British young people and adults.

PubMed

Ntouva, A; Tsakos, G; Watt, R G

2013-07-01

To report the consumption of non-milk extrinsic sugars (NMES) among a low-income UK sample, compare it with nationally representative estimates and examine the association between socioeconomic position and NMES consumption among low income adults.Design Secondary analysis of the Low Income Diet and Nutrition Survey (LIDNS) data. Two thousand, seven hundred and ninety-six adults and 415 young people from 2,477 households.Main outcome measures Mean NMES intakes (grams) and their percentage contribution to food energy, from dietary data collected via a 24-hour recall 'multiple pass' method. The low income sample consumed more NMES than the general population sample. The percentage of food energy from NMES exceeded the 11% target, especially among adolescents (17.2% in males, 16.3% in females). After adjusting for age, men who finished full-time education aged 16 years consumed significantly more sugar (p = 0.028), whereas those who finished aged 18 consumed significantly less sugar (p = 0.023) than the reference group (finished aged 15). No significant associations were found between NMES and socioeconomic variables in women. Compared to the general population, the nutritional disadvantage of the most deprived segments of society relates primarily to excessive NMES consumption. In men, higher educational level appears to play a protective role against high sugar intakes.

Nutrient characteristics of the water masses and their seasonal variability in the eastern equatorial Indian Ocean.

PubMed

Sardessai, S; Shetye, Suhas; Maya, M V; Mangala, K R; Prasanna Kumar, S

2010-01-01

Nutrient characteristics of four water masses in the light of their thermohaline properties are examined in the eastern Equatorial Indian Ocean during winter, spring and summer monsoon. The presence of low salinity water mass with "Surface enrichments" of inorganic nutrients was observed relative to 20 m in the mixed layer. Lowest oxygen levels of 19 microM at 3 degrees N in the euphotic zone indicate mixing of low oxygen high salinity Arabian Sea waters with the equatorial Indian Ocean. The seasonal variability of nutrients was regulated by seasonally varying physical processes like thermocline elevation, meridional and zonal transport, the equatorial undercurrent and biological processes of uptake and remineralization. Circulation of Arabian Sea high salinity waters with nitrate deficit could also be seen from low N/P ratio with a minimum of 8.9 in spring and a maximum of 13.6 in winter. This large deviation from Redfield N/P ratio indicates the presence of denitrified high salinity waters with a seasonal nitrate deficit ranging from -4.85 to 1.52 in the Eastern Equatorial Indian Ocean. 2010 Elsevier Ltd. All rights reserved.

Low Muscle Mass and Breast Cancer Survival

Cancer.gov

In a new study, researchers compared the risk of death for women with breast cancer who had low skeletal muscle mass, or sarcopenia, at diagnosis and women who had adequate muscle mass. Learn what they found and what it might mean for patients in this Cancer Currents blog post.

Tracing Low-Mass Star Formation in the Magellanic Clouds

NASA Astrophysics Data System (ADS)

Petr-Gotzens, Monika; Zivkov, V.; Oliveira, J.

2017-06-01

Star formation in low metallicity environments is evidently occurring under different conditions than in our Milky Way. Lower metallicity implies a lower dust to gas ratio, most likely leading to less cooling efficiency at high density molecular cores where low mass stars are expected to form. We outline a project that aims to identify the low mass pre-main sequence populations within the Large and Small Magellanic Cloud. We developed an automatic detection algorithm that systematically analyses near-infrared colour-magnitude diagrammes constructed from the VMC (VISTA Magellanic Clouds) public survey data. In this poster we present our first results that show that we are able to detect significant numbers of PMS stars with masses down to 1.5 solar mass.

Very Low-Mass Stars with Extremely Low Metallicity in the Milky Way's Halo

NASA Astrophysics Data System (ADS)

Aoki, Wako; Beers, Timothy C.; Suda, Takuma; Honda, Satoshi; Lee, Young Sun

2016-08-01

Large surveys and follow-up spectroscopic studies in the past few decades have been providing chemical abundance data for a growing number of very metal-poor ([Fe/H] <-2) stars. Most of them are red giants or main-sequence turn-off stars having masses near 0.8 solar masses. Lower mass stars with extremely low metallicity ([Fe/H] <-3) are yet to be explored. Our high-resolution spectroscopic study for very metal-poor stars found with SDSS has identified four cool main-sequence stars with [Fe/H] <-2.5 among 137 objects (Aoki et al. 2013). The effective temperatures of these stars are 4500-5000 K, corresponding to a mass of around 0.5 solar masses. Our standard analysis of the high-resolution spectra based on 1D-LTE model atmospheres has obtained self-consistent chemical abundances for these objects, assuming small values of micro-turbulent velocities compared with giants and turn-off stars. The low temperature of the atmospheres of these objects enables us to measure their detailed chemical abundances. Interestingly, two of the four stars have extreme chemical-abundance patterns: one has the largest excesses of heavy neutron-capture elements associated with the r-process abundance pattern known to date (Aoki et al. 2010), and the other exhibits low abundances of the α-elements and odd-Z elements, suggested to be signatures of the yields of very massive stars (> 100 solar masses; Aoki et al. 2014). Although the sample size is still small, these results indicate the potential of very low-mass stars as probes to study the early stages of the Milky Way's halo formation.

Motivations for sex among low-income African American young women.

PubMed

Deardorff, Julianna; Suleiman, Ahna Ballonoff; Dal Santo, Teresa S; Flythe, Michelle; Gurdin, J Barry; Eyre, Stephen L

2013-12-01

African American young women exhibit higher risk for sexually transmitted infections, including HIV/AIDS, compared with European American women, and this is particularly true for African American women living in low-income contexts. We used rigorous qualitative methods, that is, domain analysis, including free listing (n = 20), similarity assessment (n = 25), and focus groups (four groups), to elicit self-described motivations for sex among low-income African American young women (19-22 years). Analyses revealed six clusters: Love/Feelings, For Fun, Curiosity, Pressured, For Money, and For Material Things. Focus groups explored how African American women interpreted the clusters in light of condom use expectations. Participants expressed the importance of using condoms in risky situations, yet endorsed condom use during casual sexual encounters less than half the time. This study highlights the need for more effective intervention strategies to increase condom use expectations among low-income African American women, particularly in casual relationships where perceived risk is already high.

Interacting influences of gender and chronic pain status on parasympathetically mediated heart rate variability in adolescents and young adults.

PubMed

Walker, Lynn S; Stone, Amanda L; Smith, Craig A; Bruehl, Stephen; Garber, Judy; Puzanovova, Martina; Diedrich, André

2017-08-01

Considerable research links chronic pain to autonomic nervous system (ANS) dysfunction, specifically low heart rate variability (HRV) mediated by reduced parasympathetic activity. However, little is known about factors that influence ANS function in chronic pain. The ANS is the primary pathway for brain-gut communication, making it of particular interest in gastrointestinal disorders, such as irritable bowel syndrome, characterized by functional abdominal pain (FAP). We evaluated the relation of sex, pain severity, and psychological stress to ANS function in adolescents/young adults from a database of pediatric FAP and control participants enrolled 8 years earlier in a prospective study of pain. At follow-up in adolescence/young adulthood (Mean age = 19.46, SD = 3.48), we classified participants as Pain-Remit (n = 130), Pain-Persist (n = 96), and pain-free controls (n = 123). We recorded electrocardiogram data at rest and during laboratory stressors. Results demonstrated significantly lower HRV in Pain-Persist females compared with Pain-Remit females, female controls, and all males regardless of pain category. Spectral analysis of electrocardiogram showed that Pain-Persist females had reduced power in the high frequency domain of cardiac activity, ie, reduced parasympathetic "braking" of sympathetic activity, both at rest and during stress. Pain-Remit females exhibited levels of autonomic imbalance intermediate between those of females with persistent FAP and all other participants. Parasympathetically mediated low HRV in young women with persistent FAP may reflect a peripheral mechanism (eg, gut dysfunction) or a central nervous system mechanism (eg, pain amplification or poor emotion self-regulation) involving prolonged sympathetic activation.

Spitzer IRS Observations of Low-Mass Seyfert Galaxies

NASA Astrophysics Data System (ADS)

Thornton, Carol E.; Barth, A. J.; Ho, L. C.; Greene, J. E.

2010-01-01

We present results from Spitzer IRS observations of a sample of 41 Seyfert galaxies with estimated black hole masses below 106 solar masses, including objects from the SDSS-selected samples of Seyfert 1 galaxies from Greene & Ho (2004) and Seyfert 2 galaxies from Barth et al. (2008), as well as NGC 4395 and POX 52. We use the IDL code PAHFIT (Smith et al. 2007) to derive measurements of continuum shapes and narrow emission line and PAH luminosities from the low-resolution spectra in order to examine the dust emission properties of these objects and investigate the relationship between Type 1 and Type 2 AGNs at low luminosities and low masses, to search for evidence of star formation, and to use emission-line diagnostics to constrain physical conditions within the narrow-line regions.

Community influences on modern contraceptive use among young women in low and middle-income countries: a cross-sectional multi-country analysis.

PubMed

Mutumba, Massy; Wekesa, Eliud; Stephenson, Rob

2018-04-02

Despite investment in family planning programs and education, unmet need for family planning remains high among young women (aged 15-24) in low and middle-income countries, increasing the risk for unwanted pregnancies and adverse social and reproductive health outcomes. There is a dearth of cross-national research that identifies the differential impact of community level factors among youth in low and middle-income countries (LMICs), which is imperative for the design of structural level interventions aimed at increasing family planning use. Grounded in the socio-ecological framework, this paper utilizes Demographic and Health Survey (DHS) from 52 LMICs to examine the influence of community level reproductive, gender, fertility, literacy and economic indicators on modern contraceptive use among female youth. Analyses are conducted using multi-level logistic regressions with random community-level effects. Our findings highlight the positive influence of community level education attainment and negative influence of gender and fertility related norms on young women's contraceptive use. Additionally, increased exposure to mass media did not positively influence young women's uptake of modern contraceptive methods. Taken together, findings indicate that young women's contraceptive decision-making is greatly shaped by their social contexts. The commonalities and regional variations in community level influences provide support for both structural level interventions and tailored regional approaches to family planning interventions.

Time-variable gravity fields and ocean mass change from 37 months of kinematic Swarm orbits

NASA Astrophysics Data System (ADS)

Lück, Christina; Kusche, Jürgen; Rietbroek, Roelof; Löcher, Anno

2018-03-01

Measuring the spatiotemporal variation of ocean mass allows for partitioning of volumetric sea level change, sampled by radar altimeters, into mass-driven and steric parts. The latter is related to ocean heat change and the current Earth's energy imbalance. Since 2002, the Gravity Recovery and Climate Experiment (GRACE) mission has provided monthly snapshots of the Earth's time-variable gravity field, from which one can derive ocean mass variability. However, GRACE has reached the end of its lifetime with data degradation and several gaps occurred during the last years, and there will be a prolonged gap until the launch of the follow-on mission GRACE-FO. Therefore, efforts focus on generating a long and consistent ocean mass time series by analyzing kinematic orbits from other low-flying satellites, i.e. extending the GRACE time series. Here we utilize data from the European Space Agency's (ESA) Swarm Earth Explorer satellites to derive and investigate ocean mass variations. For this aim, we use the integral equation approach with short arcs (Mayer-Gürr, 2006) to compute more than 500 time-variable gravity fields with different parameterizations from kinematic orbits. We investigate the potential to bridge the gap between the GRACE and the GRACE-FO mission and to substitute missing monthly solutions with Swarm results of significantly lower resolution. Our monthly Swarm solutions have a root mean square error (RMSE) of 4.0 mm with respect to GRACE, whereas directly estimating constant, trend, annual, and semiannual (CTAS) signal terms leads to an RMSE of only 1.7 mm. Concerning monthly gaps, our CTAS Swarm solution appears better than interpolating existing GRACE data in 13.5 % of all cases, when artificially removing one solution. In the case of an 18-month artificial gap, 80.0 % of all CTAS Swarm solutions were found closer to the observed GRACE data compared to interpolated GRACE data. Furthermore, we show that precise modeling of non-gravitational forces

Characterizing the Atmosphere of a Young Planet

NASA Technical Reports Server (NTRS)

Marley, Mark

2016-01-01

Since the discovery of the young, directly imaged planet 51 Eri b, its emergent spectrum has proved challenging to interpret. The initial discovery paper (Macintosh et al. 2015) interpreted the spectrum as indicative of a low mass (few Jupiter masses), effective temperature near 700 degrees Kelvin, and partial cloudiness. Subsequent observations in the K band, however, seem to invalidate the early models. In addition, newly improved photochemical data point to the likely presence of exotic haze species in the atmosphere. In my presentation I will explore the photochemistry of the atmosphere and discuss whether disequilibrium chemistry, hazes, clouds, or non-solar abundances of heavy elements may be responsible for the unusual spectrum of this planet. The implications for the interpretation of other young Jupiters in this mass and effective temperature range will also be considered.

Accessory Cavitated Uterine Mass: A Rare Cause of Severe Dysmenorrhea in Young Women.

PubMed

Paul, P G; Chopade, Gaurav; Das, Tanuka; Dhivya, N; Patil, Saurabh; Thomas, Manju

2015-01-01

We present 3 case reports of a rare Müllerian anomaly called accessory and cavitated uterine mass (ACUM), which is found in young women >30 years of age. They presented with severe dysmenorrhea refractory to medical treatment. The patients were 17, 19, and 25 years old. The patients had the classic Müllerian anomalies. The hysteroscopic examination was normal in all 3 cases, and laparoscopic examination showed a 3- to 4-cm ill-defined mass on the right half of the uterus, without any communication to the uterine cavity. The chocolate-colored material was drained in all of the cases, during excision of the mass. The myometrial defect was sutured laparoscopically. On histological examination, the mass was found to be a cystic cavity, lined by endometrial glands and stroma, which confirmed the diagnosis of ACUM. Copyright © 2015 AAGL. Published by Elsevier Inc. All rights reserved.

Orbits and masses in the young triple system TWA 5

NASA Astrophysics Data System (ADS)

Köhler, R.; Ratzka, T.; Petr-Gotzens, M. G.; Correia, S.

2013-10-01

Aims: We aim to improve the orbital elements and determine the individual masses of the components in the triple system TWA 5. Methods: Five new relative astrometric positions in the H band were recorded with the adaptive optics system at the Very Large Telescope (VLT). We combine them with data from the literature and a measurement in the Ks band. We derive an improved fit for the orbit of TWA 5Aa-b around each other. Furthermore, we use the third component, TWA 5B, as an astrometric reference to determine the motion of Aa and Ab around their center of mass and compute their mass ratio. Results: We find an orbital period of 6.03 ± 0.01 years and a semi-major axis of 63.7 ± 0.2 mas (3.2 ± 0.1 AU). With the trigonometric distance of 50.1 ± 1.8 pc, this yields a system mass of 0.9 ± 0.1 M⊙, where the error is dominated by the error of the distance. The dynamical mass agrees with the system mass predicted by a number of theoretical models if we assume that TWA5 is at the young end of the age range of the TW Hydrae association. We find a mass ratio of MAb/MAa = 1.3-0.4+0.6 , where the less luminous component Ab is more massive. This result is likely to be a consequence of the large uncertainties due to the limited orbital coverage of the observations. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 079.C-0103, 081.C-0393, 386.C-0205, 087.C-0209, 088.C-0046, 089.C-0167, and 090.C-0184.

Near-infrared Variability in the 2MASS Calibration Fields: A Search for Planetary Transit Candidates

NASA Technical Reports Server (NTRS)

Plavchan, Peter; Jura, M.; Kirkpatrick, J. Davy; Cutri, Roc M.; Gallagher, S. C.

2008-01-01

The Two Micron All Sky Survey (2MASS) photometric calibration observations cover approximately 6 square degrees on the sky in 35 'calibration fields,' each sampled in nominal photometric conditions between 562 and 3692 times during the 4 years of the 2MASS mission. We compile a catalog of variables from the calibration observations to search for M dwarfs transited by extrasolar planets. We present our methods for measuring periodic and nonperiodic flux variability. From 7554 sources with apparent K(sub s) magnitudes between 5.6 and 16.1, we identify 247 variables, including extragalactic variables and 23 periodic variables. We have discovered three M dwarf eclipsing systems, including two candidates for transiting extrasolar planets.

Very Low Mass Stars with Extremely Low Metallicity in the Milky Way's Halo

NASA Astrophysics Data System (ADS)

Aoki, Wako; Beers, Timothy C.; Takuma, Suda; Honda, Satoshi; Lee, Young Sun

2015-08-01

Large surveys and follow-up spectroscopic studies in the past few decades have been providing chemical abundance data for a growing number of very metal-poor ([Fe/H] <-2) stars. Most of them are red giants or main-sequence turn-off stars having masses near 0.8 solar masses. Lower mass stars with extremely low metallicity ([Fe/H] <-3) have yet to be well explored. Our high-resolution spectroscopic study for very metal-poor stars found with SDSS has identified four cool main-sequence stars with [Fe/H] <-2.5 among 137 objects (Aoki et al. 2013, AJ, 145, 13). The effective temperatures of these stars are 4500--5000 K, corresponding to a mass of around 0.5 solar masses. Our standard analysis of the high-resolution spectra based on 1D-LTE model atmospheres have obtained self-consistent chemical abundances for these objects, assuming small values of micro-turbulent velocities compared with giants and turn-off stars. The low temperature of the atmospheres of these objects enables us to measure their detailed chemical abundances. Interestingly, two of the four stars have extreme chemical abundance patterns: one has the largest excesses of heavy neutron-capture elements associated with the r-process abundance pattern known to date (Aoki et al. 2010, ApJL 723, L201), and the other exhibits low abundances of the alpha-elements and odd-Z elements, suggested to be the signatures of the yields of very massive stars ( >100 solar masses; Aoki et al. 2014, Science 345, 912). Although the sample size is still small, these results indicate the potential of very low-mass stars as probes to study the early stages of the Milky Way's halo formation.

Young adult outcomes of very-low-birth-weight children.

PubMed

Hack, Maureen

2006-04-01

Information on the young adult outcomes of the initial survivors of neonatal intensive care has been reported from the United States, Canada, Australia, Great Britain and other European countries. The studies have varied with regard to whether they were regional or hospital-based, their birth-weight group and gestational age, rates of survival, socio-demographic background, and measures of assessment and types of outcome studied. Despite these differences the overall results reveal that neurodevelopment and growth sequelae persist to young adulthood. Very-low-birth-weight young adults have, with few exceptions, poorer educational achievement than normal-birth-weight controls, and fewer continue with post-high-school study. Rates of employment are, however, similar. There are no major differences in general health status, but the young adults demonstrate poorer physical abilities, higher mean blood pressure and poorer respiratory function. There is no evidence of major psychiatric disorder, although anxiety and depression are reported more often. The young adults report less risk-taking than control populations. They report fairly normal social lives and quality of life. When differences are noted they are usually due to neurosensory disabilities. Longer-term studies are needed to evaluate ultimate educational and occupational achievement. It will also be important to assess the effects of preterm birth, early growth failure and catch-up growth on later metabolic and cardiovascular health.

Marine reservoir age variability and water mass distribution in the Iceland Sea

NASA Astrophysics Data System (ADS)

Eiríksson, Jón; Larsen, Gudrún; Knudsen, Karen Luise; Heinemeier, Jan; Símonarson, Leifur A.

2004-11-01

Lateglacial and Holocene tephra markers from Icelandic source volcanoes have been identified in five sediment cores from the North Icelandic shelf and correlated with tephra layers in reference soil sections in North Iceland and the GRIP ice core. Land-sea correlation of tephra markers, that have been radiocarbon dated with terrestrial material or dated by documentary evidence, provides a tool for monitoring reservoir age variability in the region. Age models developed for the shelf sediments north of Iceland, based on offshore tephrochronology on one hand and on calibrated AMS 14C datings of marine molluscs on the other, display major deviations during the last 4500 years. The inferred temporal variability in the reservoir age of the regional water masses exceeds by far the variability expected from the marine model calculations. The observed reservoir ages are generally considerably higher, by up to 450 years, than the standard model ocean. It is postulated that the intervals with increased and variable marine reservoir age reflect incursions of Arctic water masses derived from the East Greenland Current to the Iceland Sea and the North Icelandic shelf.

An UXor among FUors: Extinction-related Brightness Variations of the Young Eruptive Star V582 Aur

NASA Astrophysics Data System (ADS)

Ábrahám, P.; Kóspál, Á.; Kun, M.; Fehér, O.; Zsidi, G.; Acosta-Pulido, J. A.; Carnerero, M. I.; García-Álvarez, D.; Moór, A.; Cseh, B.; Hajdu, G.; Hanyecz, O.; Kelemen, J.; Kriskovics, L.; Marton, G.; Mező, Gy.; Molnár, L.; Ordasi, A.; Rodríguez-Coira, G.; Sárneczky, K.; Sódor, Á.; Szakáts, R.; Szegedi-Elek, E.; Szing, A.; Farkas-Takács, A.; Vida, K.; Vinkó, J.

2018-01-01

V582 Aur is an FU Ori-type young eruptive star in outburst since ∼1985. The eruption is currently in a relatively constant plateau phase, with photometric and spectroscopic variability superimposed. Here we will characterize the progenitor of the outbursting object, explore its environment, and analyze the temporal evolution of the eruption. We are particularly interested in the physical origin of the two deep photometric dips, one that occurred in 2012 and one that is ongoing since 2016. We collected archival photographic plates and carried out new optical, infrared, and millimeter-wave photometric and spectroscopic observations between 2010 and 2018, with a high sampling rate during the current minimum. Besides analyzing the color changes during fading, we compiled multiepoch spectral energy distributions and fitted them with a simple accretion disk model. Based on pre-outburst data and a millimeter continuum measurement, we suggest that the progenitor of the V582 Aur outburst is a low-mass T Tauri star with average properties. The mass of an unresolved circumstellar structure, probably a disk, is 0.04 M ⊙. The optical and near-infrared spectra demonstrate the presence of hydrogen and metallic lines, show the CO band head in absorption, and exhibit a variable Hα profile. The color variations strongly indicate that both the ∼1 yr long brightness dip in 2012 and the current minimum since 2016 are caused by increased extinction along the line of sight. According to our accretion disk models, the reddening changed from A V = 4.5 to 12.5 mag, while the accretion rate remained practically constant. Similarly to the models of the UXor phenomenon of intermediate- and low-mass young stars, orbiting disk structures could be responsible for the eclipses.

A Pan-Carina Young Stellar Object Catalog: Intermediate-mass Young Stellar Objects in the Carina Nebula Identified Via Mid-infrared Excess Emission

NASA Astrophysics Data System (ADS)

Povich, Matthew S.; Smith, Nathan; Majewski, Steven R.; Getman, Konstantin V.; Townsley, Leisa K.; Babler, Brian L.; Broos, Patrick S.; Indebetouw, Rémy; Meade, Marilyn R.; Robitaille, Thomas P.; Stassun, Keivan G.; Whitney, Barbara A.; Yonekura, Yoshinori; Fukui, Yasuo

2011-05-01

We present a catalog of 1439 young stellar objects (YSOs) spanning the 1.42 deg2 field surveyed by the Chandra Carina Complex Project (CCCP), which includes the major ionizing clusters and the most active sites of ongoing star formation within the Great Nebula in Carina. Candidate YSOs were identified via infrared (IR) excess emission from dusty circumstellar disks and envelopes, using data from the Spitzer Space Telescope (the Vela-Carina survey) and the Two-Micron All Sky Survey. We model the 1-24 μm IR spectral energy distributions of the YSOs to constrain physical properties. Our Pan-Carina YSO Catalog (PCYC) is dominated by intermediate-mass (2 M sun < m <~ 10 M sun) objects with disks, including Herbig Ae/Be stars and their less evolved progenitors. The PCYC provides a valuable complementary data set to the CCCP X-ray source catalogs, identifying 1029 YSOs in Carina with no X-ray detection. We also catalog 410 YSOs with X-ray counterparts, including 62 candidate protostars. Candidate protostars with X-ray detections tend to be more evolved than those without. In most cases, X-ray emission apparently originating from intermediate-mass, disk-dominated YSOs is consistent with the presence of low-mass companions, but we also find that X-ray emission correlates with cooler stellar photospheres and higher disk masses. We suggest that intermediate-mass YSOs produce X-rays during their early pre-main-sequence evolution, perhaps driven by magnetic dynamo activity during the convective atmosphere phase, but this emission dies off as the stars approach the main sequence. Extrapolating over the stellar initial mass function scaled to the PCYC population, we predict a total population of >2 × 104 YSOs and a present-day star formation rate (SFR) of >0.008 M sun yr-1. The global SFR in the Carina Nebula, averaged over the past ~5 Myr, has been approximately constant.

Interannual variability of mass transport in the Canary region from LADCP data

NASA Astrophysics Data System (ADS)

Comas-Rodríguez, Isis; Hernández-Guerra, Alonso; Vélez-Belchí, Pedro; Fraile-Nuez, Eugenio

2010-05-01

The variability of the Canary Current is a widely studied topic regarding its role as eastern boundary of the North Atlantic Subtropical Gyre. The Canary region provides indeed an interesting study area in terms of estimating variability scales of the Subtropical Gyre as well as the water masses dynamics. RAPROCAN (RAdial PROfunda de CANarias - Canary deep hydrographic section) is a project based on the reaching of these goals through the obtaining of hydrographic measures during cruises taking place approximately along 29°N, to the North of the Canary Archipelago, twice a year since 2006. The full depth sampling carried out allows the study of temperature and salinity distribution and the calculation of mass transports across the section. The transport estimates are compared to those obtained from previous measurements and estimates in the region. Therefore, transports and their variability through the last decade are quantified. The most significant advance made to previous works is the use of LADCP (Lowered Acoustic Doppler Current Profiler) data informing the initial geostrophic calculations. Thus, corrections are applied to each geostrophic profile considering the reference velocity obtained from LADCP data. ADCP-referenced transport estimates are obtained, providing a successful comparison between the velocity fields obtained from the hydrographic measures. While this work shows the interannual variability observed in winter since 1997, preliminary results confirm previous hypotheses about the magnitude of the Canary Current. Those results including LADCP data also provide new aspects in the circulation distribution across the Canary Archipelago. Also moored current meter data were taken into account in the up close study of the Current through the Lanzarote Passage. Interesting conclusions were drawn that certify the usefulness of LADCP data in referencing geostrophic calculations, while corroborating the results obtained through this methodology. Hence

Speed but not amplitude of visual feedback exacerbates force variability in older adults.

PubMed

Kim, Changki; Yacoubi, Basma; Christou, Evangelos A

2018-06-23

Magnification of visual feedback (VF) impairs force control in older adults. In this study, we aimed to determine whether the age-associated increase in force variability with magnification of visual feedback is a consequence of increased amplitude or speed of visual feedback. Seventeen young and 18 older adults performed a constant isometric force task with the index finger at 5% of MVC. We manipulated the vertical (force gain) and horizontal (time gain) aspect of the visual feedback so participants performed the task with the following VF conditions: (1) high amplitude-fast speed; (2) low amplitude-slow speed; (3) high amplitude-slow speed. Changing the visual feedback from low amplitude-slow speed to high amplitude-fast speed increased force variability in older adults but decreased it in young adults (P < 0.01). Changing the visual feedback from low amplitude-slow speed to high amplitude-slow speed did not alter force variability in older adults (P > 0.2), but decreased it in young adults (P < 0.01). Changing the visual feedback from high amplitude-slow speed to high amplitude-fast speed increased force variability in older adults (P < 0.01) but did not alter force variability in young adults (P > 0.2). In summary, increased force variability in older adults with magnification of visual feedback was evident only when the speed of visual feedback increased. Thus, we conclude that in older adults deficits in the rate of processing visual information and not deficits in the processing of more visual information impair force control.

A survey for low-mass stellar and substellar members of the Hyades open cluster

NASA Astrophysics Data System (ADS)

Melnikov, Stanislav; Eislöffel, Jochen

2018-03-01

Context. Unlike young open clusters (with ages < 250 Myr), the Hyades cluster (age 600 Myr) has a clear deficit of very low-mass stars (VLM) and brown dwarfs (BD). Since this open cluster has a low stellar density and covers several tens of square degrees on the sky, extended surveys are required to improve the statistics of the VLM/BD objects in the cluster. Aim. We search for new VLM stars and BD candidates in the Hyades cluster to improve the present-day cluster mass function down to substellar masses. Methods: An imaging survey of the Hyades with a completeness limit of 21.m5 in the R band and 20.m5 in the I band was carried out with the 2k × 2k CCD Schmidt camera at the 2 m Alfred Jensch Telescope in Tautenburg. We performed a photometric selection of the cluster member candidates by combining results of our survey with 2MASS JHKs photometry Results: We present a photometric and proper motion survey covering 23.4 deg2 in the Hyades cluster core region. Using optical/IR colour-magnitude diagrams, we identify 66 photometric cluster member candidates in the magnitude range 14.m7 < I < 20.m5. The proper motion measurements are based on several all-sky surveys with an epoch difference of 60-70 yr for the bright objects. The proper motions allowed us to discriminate the cluster members from field objects and resulted in 14 proper motion members of the Hyades. We rediscover Hy 6 as a proper motion member and classify it as a substellar object candidate (BD) based on the comparison of the observed colour-magnitude diagram with theoretical model isochrones. Conclusions: With our results, the mass function of the Hyades continues to be shallow below 0.15 M⊙ indicating that the Hyades have probably lost their lowest mass members by means of dynamical evolution. We conclude that the Hyades core represents the "VLM/BD desert" and that most of the substeller objects may have already left the volume of the cluster.

PN G068.1+11.0: A young pre-cataclysmic variable with an extremely hot primary

NASA Astrophysics Data System (ADS)

Mitrofanova, A. A.; Shimansky, V. V.; Borisov, N. V.; Spiridonova, O. I.; Gabdeev, M. M.

2016-02-01

An analysis of spectroscopic and photometric data for the young pre-cataclysmic variable (PCV) PN G068.1+11.0, which passed through its common-envelope stage relatively recently, is presented. The spectroscopic and photometric data were obtained with the 6-m telescope and Zeiss-1000 telescope of the Special Astrophysical Observatory. The light curves show sinusoidal brightness variations with the orbital-period time scale and brightness-variation amplitudes of Δ m = 1. m41, 1. m62, and 1. m57 in the B, V, and R bands, respectively. The system's spectrum exhibits weak HI (H β-H δ) andHeII λλ4541, 4686, 5411 Å absorption lines during the phases of minimum brightness, as well as HI, HeII, CIII, CIV, NIII, and OII emission lines whose intensity variations are synchronized with variations of the integrated brightness of the system. The emission-line formation in the spectra can be fully explained by the effects of fluorescence of the ultraviolet light from the primary at the surface of the cool star. All the characteristics of the optical light of PN G068.1+11.0 confirm that it is a young PCV containing sdO subdwarf. The radial velocities were measured from a blend of lines of moderately light elements, CIII+NIII λ4640 Å, which is formed at the surface of the secondary due to reflection effects. The ephemeris of the system has been improved through a joint analysis of the radial-velocity curves and light curves of pre-cataclysmic variable, using modelling of the reflection effects. The fundamental parameters of PN G068.1+11.0 have been determined using two evolutionary tracks for planetary-nebula nuclei of different masses (0.7 M ⊙and 0.78 M ⊙). The model spectra for the system and a comparison with the observations demonstrate the possibility of refining the components' effective temperatures if the quality of the spectra used is improved.

Temporal and spatial variabilities of Antarctic ice mass changes inferred by GRACE in a Bayesian framework

NASA Astrophysics Data System (ADS)

Wang, L.; Davis, J. L.; Tamisiea, M. E.

2017-12-01

The Antarctic ice sheet (AIS) holds about 60% of all fresh water on the Earth, an amount equivalent to about 58 m of sea-level rise. Observation of AIS mass change is thus essential in determining and predicting its contribution to sea level. While the ice mass loss estimates for West Antarctica (WA) and the Antarctic Peninsula (AP) are in good agreement, what the mass balance over East Antarctica (EA) is, and whether or not it compensates for the mass loss is under debate. Besides the different error sources and sensitivities of different measurement types, complex spatial and temporal variabilities would be another factor complicating the accurate estimation of the AIS mass balance. Therefore, a model that allows for variabilities in both melting rate and seasonal signals would seem appropriate in the estimation of present-day AIS melting. We present a stochastic filter technique, which enables the Bayesian separation of the systematic stripe noise and mass signal in decade-length GRACE monthly gravity series, and allows the estimation of time-variable seasonal and inter-annual components in the signals. One of the primary advantages of this Bayesian method is that it yields statistically rigorous uncertainty estimates reflecting the inherent spatial resolution of the data. By applying the stochastic filter to the decade-long GRACE observations, we present the temporal variabilities of the AIS mass balance at basin scale, particularly over East Antarctica, and decipher the EA mass variations in the past decade, and their role in affecting overall AIS mass balance and sea level.

Bone mass in physicians: a Howard University Hospital pilot study.

PubMed

Reyes, May O; Archer, Juanita A; Nunlee-Bland, Gail; Daniel, Gilbert; Morgan, Odette A; Makambi, Kepher

2004-03-01

This observational cross-sectional study was done to determine bone mass in physicians and to determine if variables, such as calcium intake and exercise, were related to their bone mass. One-hundred physicians of different ethnicities (African, African American, Asian, Caribbean, and Hispanic) were studied. Using dual-energy x-ray absorptiometry (DEXA), bone mass (BMD) of the lumbar spine and hips was measured. A validated questionnaire was used to determine the daily calcium intake and exercise. Student t-test, logistic regression, and Pearson chi-square were used to analyze the data. The study population consisted of 52% men and 48% women, with a mean age of 42 years old and a body mass index of 18.5 to 39.9 kg/m2. Low BMD occurred in 68% of the physicians (osteoporosis in 12%, osteopenia in 56%). Low calcium intake was found in 71%-14% of whom had osteoporosis and 49% osteopenia. Two-thirds of the physicians had inadequate exercise; 57% of this group had decreased BMD (osteoporosis in 9%, osteopenia in 38%). There was no statistical significance between BMD and calcium intake or exercise. A high percentage of the physicians in this unique study had a reduced BMD. Most of the physicians with low BMD were less than 45 years of age. This study indicates the need to define BMD in a larger cohort of young, ethnically diverse clinicians, and other health workers.

Bone mass in physicians: a Howard University Hospital pilot study.

PubMed Central

Reyes, May O.; Archer, Juanita A.; Nunlee-Bland, Gail; Daniel, Gilbert; Morgan, Odette A.; Makambi, Kepher

2004-01-01

PURPOSE: This observational cross-sectional study was done to determine bone mass in physicians and to determine if variables, such as calcium intake and exercise, were related to their bone mass. METHODS: One-hundred physicians of different ethnicities (African, African American, Asian, Caribbean, and Hispanic) were studied. Using dual-energy x-ray absorptiometry (DEXA), bone mass (BMD) of the lumbar spine and hips was measured. A validated questionnaire was used to determine the daily calcium intake and exercise. Student t-test, logistic regression, and Pearson chi-square were used to analyze the data. RESULTS: The study population consisted of 52% men and 48% women, with a mean age of 42 years old and a body mass index of 18.5 to 39.9 kg/m2. Low BMD occurred in 68% of the physicians (osteoporosis in 12%, osteopenia in 56%). Low calcium intake was found in 71%-14% of whom had osteoporosis and 49% osteopenia. Two-thirds of the physicians had inadequate exercise; 57% of this group had decreased BMD (osteoporosis in 9%, osteopenia in 38%). There was no statistical significance between BMD and calcium intake or exercise. CONCLUSION: A high percentage of the physicians in this unique study had a reduced BMD. Most of the physicians with low BMD were less than 45 years of age. This study indicates the need to define BMD in a larger cohort of young, ethnically diverse clinicians, and other health workers. Images Figure 1 Figure 2 PMID:15040511

Theoretical uncertainties on the radius of low- and very-low-mass stars

NASA Astrophysics Data System (ADS)

Tognelli, E.; Prada Moroni, P. G.; Degl'Innocenti, S.

2018-05-01

We performed an analysis of the main theoretical uncertainties that affect the radius of low- and very-low-mass stars predicted by current stellar models. We focused on stars in the mass range 0.1-1 M⊙, on both the zero-age main sequence (ZAMS) and on 1, 2, and 5 Gyr isochrones. First, we quantified the impact on the radius of the uncertainty of several quantities, namely the equation of state, radiative opacity, atmospheric models, convection efficiency, and initial chemical composition. Then, we computed the cumulative radius error stripe obtained by adding the radius variation due to all the analysed quantities. As a general trend, the radius uncertainty increases with the stellar mass. For ZAMS structures the cumulative error stripe of very-low-mass stars is about ±2 and ±3 per cent, while at larger masses it increases up to ±4 and ±5 per cent. The radius uncertainty gets larger and age dependent if isochrones are considered, reaching for M ˜ 1 M⊙ about +12(-15) per cent at an age of 5 Gyr. We also investigated the radius uncertainty at a fixed luminosity. In this case, the cumulative error stripe is the same for both ZAMS and isochrone models and it ranges from about ±4 to +7 and +9(-5) per cent. We also showed that the sole uncertainty on the chemical composition plays an important role in determining the radius error stripe, producing a radius variation that ranges between about ±1 and ±2 per cent on ZAMS models with fixed mass and about ±3 and ±5 per cent at a fixed luminosity.

Supergiants and their shells in young globular clusters

NASA Astrophysics Data System (ADS)

Szécsi, Dorottya; Mackey, Jonathan; Langer, Norbert

2018-04-01

Context. Anomalous surface abundances are observed in a fraction of the low-mass stars of Galactic globular clusters, that may originate from hot-hydrogen-burning products ejected by a previous generation of massive stars. Aims: We aim to present and investigate a scenario in which the second generation of polluted low-mass stars can form in shells around cool supergiant stars within a young globular cluster. Methods: Simulations of low-metallicity massive stars (Mi 150-600 M⊙) show that both core-hydrogen-burning cool supergiants and hot ionizing stellar sources are expected to be present simulaneously in young globular clusters. Under these conditions, photoionization-confined shells form around the supergiants. We have simulated such a shell, investigated its stability and analysed its composition. Results: We find that the shell is gravitationally unstable on a timescale that is shorter than the lifetime of the supergiant, and the Bonnor-Ebert mass of the overdense regions is low enough to allow star formation. Since the low-mass stellar generation formed in this shell is made up of the material lost from the supergiant, its composition necessarily reflects the composition of the supergiant wind. We show that the wind contains hot-hydrogen-burning products, and that the shell-stars therefore have very similar abundance anomalies that are observed in the second generation stars of globular clusters. Considering the mass-budget required for the second generation star-formation, we offer two solutions. Either a top-heavy initial mass function is needed with an index of -1.71 to -2.07. Alternatively, we suggest the shell-stars to have a truncated mass distribution, and solve the mass budget problem by justifiably accounting for only a fraction of the first generation. Conclusions: Star-forming shells around cool supergiants could form the second generation of low-mass stars in Galactic globular clusters. Even without forming a photoionizaton-confined shell, the

Gestational weight gain and subsequent postpartum weight loss among young, low-income, ethnic minority women.

PubMed

Gould Rothberg, Bonnie E; Magriples, Urania; Kershaw, Trace S; Rising, Sharon Schindler; Ickovics, Jeannette R

2011-01-01

Document weight change trajectories that lead to gestational weight gain or postpartum weight loss outside clinical recommendations established by the Institute of Medicine. Women aged 14-25 receiving prenatal care and delivering singleton infants at term (n = 427). Medical record review and 4 structured interviews conducted: second and third trimester, 6- and 12-months postpartum. Longitudinal mixed modeling to evaluate weight change trajectories. Only 22% of participants gained gestational weight within Institute of Medicine guidelines. There were 62% that exceeded maximum recommendations-more common among those overweight/obese (body mass index ≥25.0; P < .0001). 52% retained ≥10 lb 1-year postpartum. Increased weight gain and retention documented among smokers and women with pregnancy-induced hypertension; breastfeeding promoted postpartum weight loss (all P < .02). Body mass index by race interaction suggested healthier outcomes for Latinas (P = .02). Excessive pregnancy weight gain and inadequate postpartum weight loss are highly prevalent among young low-income ethnic minority women. Pregnancy and postpartum are critical junctures for weight management interventions. Copyright © 2011 Mosby, Inc. All rights reserved.

Low-mass galaxy assembly in simulations: regulation of early star formation by radiation from massive stars

NASA Astrophysics Data System (ADS)

Trujillo-Gomez, Sebastian; Klypin, Anatoly; Colín, Pedro; Ceverino, Daniel; Arraki, Kenza S.; Primack, Joel

2015-01-01

Despite recent success in forming realistic present-day galaxies, simulations still form the bulk of their stars earlier than observations indicate. We investigate the process of stellar mass assembly in low-mass field galaxies, a dwarf and a typical spiral, focusing on the effects of radiation from young stellar clusters on the star formation (SF) histories. We implement a novel model of SF with a deterministic low efficiency per free-fall time, as observed in molecular clouds. Stellar feedback is based on observations of star-forming regions, and includes radiation pressure from massive stars, photoheating in H II regions, supernovae and stellar winds. We find that stellar radiation has a strong effect on the formation of low-mass galaxies, especially at z > 1, where it efficiently suppresses SF by dispersing cold and dense gas, preventing runaway growth of the stellar component. This behaviour is evident in a variety of observations but had so far eluded analytical and numerical models without radiation feedback. Compared to supernovae alone, radiation feedback reduces the SF rate by a factor of ˜100 at z ≲ 2, yielding rising SF histories which reproduce recent observations of Local Group dwarfs. Stellar radiation also produces bulgeless spiral galaxies and may be responsible for excess thickening of the stellar disc. The galaxies also feature rotation curves and baryon fractions in excellent agreement with current data. Lastly, the dwarf galaxy shows a very slow reduction of the central dark matter density caused by radiation feedback over the last ˜7 Gyr of cosmic evolution.

Mass loss from solar-type stars

NASA Technical Reports Server (NTRS)

Hartmann, L.

1985-01-01

The present picture of mass loss from solar-type (low-mass) stars is described, with special emphasis on winds from pre-main-sequence stars. Attention is given to winds from T Tauri stars and to angular momentum loss. Prospects are good for further advances in our understanding of the powerful mass loss observed from young stars; ultraviolet spectra obtainable with the Space Telescope should provide better estimates of mass loss rates and a clearer picture of physical conditions in the envelopes of these stars. To understand the mass ejection from old, slowly rotating main-sequence stars, we will have to study the sun.

ACCURATE LOW-MASS STELLAR MODELS OF KOI-126

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feiden, Gregory A.; Chaboyer, Brian; Dotter, Aaron, E-mail: gregory.a.feiden@dartmouth.edu

2011-10-10

The recent discovery of an eclipsing hierarchical triple system with two low-mass stars in a close orbit (KOI-126) by Carter et al. appeared to reinforce the evidence that theoretical stellar evolution models are not able to reproduce the observational mass-radius relation for low-mass stars. We present a set of stellar models for the three stars in the KOI-126 system that show excellent agreement with the observed radii. This agreement appears to be due to the equation of state implemented by our code. A significant dispersion in the observed mass-radius relation for fully convective stars is demonstrated; indicative of the influencemore » of physics currently not incorporated in standard stellar evolution models. We also predict apsidal motion constants for the two M dwarf companions. These values should be observationally determined to within 1% by the end of the Kepler mission.« less

The Solar Neighborhood. XXXX. Parallax Results from the CTIOPI 0.9 m Program: New Young Stars Near the Sun

NASA Astrophysics Data System (ADS)

Bartlett, Jennifer L.; Lurie, John C.; Riedel, Adric; Ianna, Philip A.; Jao, Wei-Chun; Henry, Todd J.; Winters, Jennifer G.; Finch, Charlie T.; Subasavage, John P.

2017-10-01

As a step toward completing and characterizing the census of the solar neighborhood, we present astrometric, photometric, and spectroscopic observations of 32 systems observed with the Cerro Tololo Inter-American Observatory 0.9 m and 1.5 m telescopes. Astrometry from the 0.9 m indicates that among the 17 systems that had no previous published trigonometric parallaxes, 14 are within 25 pc. In the full sample, nine systems have proper motions larger than 0.″5 yr-1, including 2MASS J02511490-0352459, which exceeds 2.″0 yr-1. VRI photometry from the 0.9 m and optical spectra from the 1.5 m indicate that the targets have V = 11-22 mag and spectral types M3.0V-L3.0V. For 2MASS J23062928-0502285 (TRAPPIST-1), we present updated astrometry and photometric variability based on over 12 years of observations. Of the nine binaries in the sample, two promise mass determinations in the next decade: LHS 6167AB, an M4.5V system for which we present an accurate parallax placing the binary at 9.7 pc, and 2MASS J23515048-2537367AB, an M8.5V system at 21.1 pc for which we present the first evidence of an unseen, low-mass companion. Most importantly, Na I and K I gravity indicators, Hα measurements, long-term photometric variability, locations on the H-R diagram, and kinematic assessments indicate that as many as 13 of the systems are young, including candidate members of young moving groups, with ages less than ˜120 Myr.

The Solar Neighborhood. XXXX. Parallax Results from the CTIOPI 0.9 m Program: New Young Stars Near the Sun

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bartlett, Jennifer L.; Finch, Charlie T.; Lurie, John C.

As a step toward completing and characterizing the census of the solar neighborhood, we present astrometric, photometric, and spectroscopic observations of 32 systems observed with the Cerro Tololo Inter-American Observatory 0.9 m and 1.5 m telescopes. Astrometry from the 0.9 m indicates that among the 17 systems that had no previous published trigonometric parallaxes, 14 are within 25 pc. In the full sample, nine systems have proper motions larger than 0.″5 yr{sup −1}, including 2MASS J02511490-0352459, which exceeds 2.″0 yr{sup −1}. VRI photometry from the 0.9 m and optical spectra from the 1.5 m indicate that the targets have Vmore »  = 11–22 mag and spectral types M3.0V–L3.0V. For 2MASS J23062928-0502285 (TRAPPIST-1), we present updated astrometry and photometric variability based on over 12 years of observations. Of the nine binaries in the sample, two promise mass determinations in the next decade: LHS 6167AB, an M4.5V system for which we present an accurate parallax placing the binary at 9.7 pc, and 2MASS J23515048-2537367AB, an M8.5V system at 21.1 pc for which we present the first evidence of an unseen, low-mass companion. Most importantly, Na i and K i gravity indicators, H α measurements, long-term photometric variability, locations on the H-R diagram, and kinematic assessments indicate that as many as 13 of the systems are young, including candidate members of young moving groups, with ages less than ∼120 Myr.« less

Chandra Detection of an Evolved Population of Young Stars in Serpens South

NASA Astrophysics Data System (ADS)

Winston, E.; Wolk, S. J.; Gutermuth, R.; Bourke, T. L.

2018-06-01

We present a Chandra study of the deeply embedded Serpens South star-forming region, examining cluster structure and disk properties at the earliest stages. In total, 152 X-ray sources are detected. Combined with Spitzer and 2MASS photometry, 66 X-ray sources are reliably matched to an IR counterpart. We identify 21 class I, 6 flat spectrum, 16 class II, and 18 class III young stars; 5 were unclassified. Eighteen sources were variable in X-rays, 8 exhibiting flare-like emission and one source being periodic. The cluster’s X-ray luminosity distance was estimated: the best match was to the nearer distance of 260 pc for the front of the Aquila Rift complex. The ratio of N H to A K is found to be ∼0.68 × 1022, similar to that measured in other young low-mass regions, but lower than that measured in the interstellar medium and high-mass clusters (∼(1.6–2) × 1022). We find that the spatial distribution closely follows that of the dense filament from which the stars have formed, with the class II population still strongly associated with the filament. There are four subclusters in the field, with three forming knots in the filament, and a fourth to the west, which may not be associated but may be contributing to the distributed class III population. A high percentage of diskless class IIIs (upper limit 30% of classified X-ray sources) in such a young cluster could indicate that processing of disks is influenced by the cluster environment and is not solely dependent on timescale.

High fat diet promotes achievement of peak bone mass in young rats.

PubMed

Malvi, Parmanand; Piprode, Vikrant; Chaube, Balkrishna; Pote, Satish T; Mittal, Monika; Chattopadhyay, Naibedya; Wani, Mohan R; Bhat, Manoj Kumar

2014-12-05

The relationship between obesity and bone is complex. Epidemiological studies demonstrate positive as well as negative correlation between obesity and bone health. In the present study, we investigated the impact of high fat diet-induced obesity on peak bone mass. After 9 months of feeding young rats with high fat diet, we observed obesity phenotype in rats with increased body weight, fat mass, serum triglycerides and cholesterol. There were significant increases in serum total alkaline phosphatase, bone mineral density and bone mineral content. By micro-computed tomography (μ-CT), we observed a trend of better trabecular bones with respect to their microarchitecture and geometry. This indicated that high fat diet helps in achieving peak bone mass and microstructure at younger age. We subsequently shifted rats from high fat diet to normal diet for 6 months and evaluated bone/obesity parameters. It was observed that after shifting rats from high fat diet to normal diet, fat mass, serum triglycerides and cholesterol were significantly decreased. Interestingly, the gain in bone mineral density, bone mineral content and trabecular bone parameters by HFD was retained even after body weight and obesity were normalized. These results suggest that fat rich diet during growth could accelerate achievement of peak bone mass that is sustainable even after withdrawal of high fat diet.

WHERE ARE THE LOW-MASS POPULATION III STARS?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ishiyama, Tomoaki; Sudo, Kae; Yokoi, Shingo

2016-07-20

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 H{sub 2} 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 {sub ⊙} 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 survivorsmore » 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 {sub ⊙}.« less

Association Between MCT1 A1470T Polymorphism and Fat-Free Mass in Well-Trained Young Soccer Players.

PubMed

Massidda, Myosotis; Eynon, Nir; Bachis, Valeria; Corrias, Laura; Culigioni, Claudia; Cugia, Paolo; Scorcu, Marco; Calò, Carla M

2016-04-01

The aim of this study was to investigate the association between the MCT1 A1470T polymorphism and fat-free mass in young Italian elite soccer players. Participants were 128 Italian male soccer players. Fat-free mass was estimated for each of the soccer player using age- and gender-specific formulas with plicometry. Genotyping for the MCT1 A1470T polymorphism was performed using polymerase chain reaction. The MCT1 A1470T genotypes were in agreement with the Hardy-Weinberg equilibrium distribution. The percentage of fat-free mass was significantly higher in soccer players with the TT genotype and in the T-allele-dominant model group (TT + AT) compared with the soccer players with the AA genotype. The MCT1 T allele is associated with the percentage of fat-free mass in young elite male soccer players. Elucidating the genetic basis of body composition in athletes could potentially be used as an additional tool for strength and conditioning professionals in planning and adjusting training. However, these results are preliminary and need to be replicated in more cohorts.

Dynamic characteristics of a variable-mass flexible missile

NASA Technical Reports Server (NTRS)

Meirovitch, L.; Bankovskis, J.

1970-01-01

The general motion of a variable mass flexible missile with internal flow and aerodynamic forces is considered. The resulting formulation comprises six ordinary differential equations for rigid body motion and three partial differential equations for elastic motion. The simultaneous differential equations are nonlinear and possess time-dependent coefficients. The differential equations are solved by a semi-analytical method leading to a set of purely ordinary differential equations which are then solved numerically. A computer program was developed for the numerical solution and results are presented for a given set of initial conditions.

Reconnaissance of Young M Dwarfs: Locating the Elusive Majority of Nearby Moving Groups

NASA Astrophysics Data System (ADS)

Bowler, Brendan; Liu, Michael; Riaz, Basmah; Gizis, John; Shkolnik, Evgenya

2013-08-01

With ages between ~8-120 Myr and distances lsim;80 pc, young moving group members make excellent targets for detailed studies of pre-main sequence evolution and exoplanet imaging surveys. We propose a multi-semester spectroscopic program to confirm our sample of ~1300 X-ray-selected active M dwarfs, about one-third of which are expected to be members of young moving groups. Our program consists of three parts: a reconnaissance phase of low-resolution spectroscopy to vet unlikely association members, radial velocity observations to confirm group membership, and deep adaptive optics imaging to study the architecture and demographics of giant planets around low-mass stars. We will also exploit our rich sample to study the evolution of chromospheric and coronal activity in low-mass stars with unprecedented precision. Altogether, this program will roughly double the population of M dwarfs in young moving groups, providing new targets for a broad range of star and planet formation studies in the near-future.

Measuring high spatiotemporal variability in saltation intensity using a low-cost Saltation Detection System: Wind tunnel and field experiments

NASA Astrophysics Data System (ADS)

de Winter, W.; van Dam, D. B.; Delbecque, N.; Verdoodt, A.; Ruessink, B. G.; Sterk, G.

2018-04-01

The commonly observed over prediction of aeolian saltation transport on sandy beaches is, at least in part, caused by saltation intermittency. To study small-scale saltation processes, high frequency saltation sensors are required on a high spatial resolution. Therefore, we developed a low-cost Saltation Detection System (SalDecS) with the aim to measure saltation intensity at a frequency of 10 Hz and with a spatial resolution of 0.10 m in wind-normal direction. Linearity and equal sensitivity of the saltation sensors were investigated during wind tunnel and field experiments. Wind tunnel experiments with a set of 7 SalDec sensors revealed that the variability of sensor sensitivity is at maximum 9% during relatively low saltation intensities. During more intense saltation the variability of sensor sensitivity decreases. A sigmoidal fit describes the relation between mass flux and sensor output measured during 5 different wind conditions. This indicates an increasing importance of sensor saturation with increasing mass flux. We developed a theoretical model to simulate and describe the effect of grain size, grain velocity and saltation intensity on sensor saturation. Time-averaged field measurements revealed sensitivity equality for 85 out of a set of 89 horizontally deployed SalDec sensors. On these larger timescales (hours) saltation variability imposed by morphological features, such as sand strips, can be recognized. We conclude that the SalDecS can be used to measure small-scale spatiotemporal variabilities of saltation intensity to investigate saltation characteristics related to wind turbulence.

Multiwavelength study of the low-luminosity outbursting young star HBC 722

NASA Astrophysics Data System (ADS)

Kóspál, Á.; Ábrahám, P.; Acosta-Pulido, J. A.; Dunham, M. M.; García-Álvarez, D.; Hogerheijde, M. R.; Kun, M.; Moór, A.; Farkas, A.; Hajdu, G.; Hodosán, G.; Kovács, T.; Kriskovics, L.; Marton, G.; Molnár, L.; Pál, A.; Sárneczky, K.; Sódor, Á.; Szakáts, R.; Szalai, T.; Szegedi-Elek, E.; Szing, A.; Tóth, I.; Vida, K.; Vinkó, J.

2016-11-01

Context. HBC 722 (V2493 Cyg) is a young eruptive star in outburst since 2010. Spectroscopic evidence suggests that the source is an FU Orionis-type object, with an atypically low outburst luminosity. Aims: Because it was well characterized in the pre-outburst phase, HBC 722 is one of the few FUors from which we can learn about the physical changes and processes associated with the eruption, including the role of the circumstellar environment. Methods: We monitored the source in the BVRIJHKS bands from the ground and at 3.6 and 4.5 μm from space with the Spitzer Space Telescope. We analyzed the light curves and studied the evolving spectral energy distribution by fitting a series of steady accretion disk models at many epochs covering the outburst. We also analyzed the spectral properties of the source based on our new optical and infrared spectra, comparing our line inventory with those published in the literature for other epochs. We also mapped HBC 722 and its surroundings at millimeter wavelengths. Results: From the light-curve analysis we conclude that the first peak of the outburst in 2010 September was mainly due to an abrupt increase in the accretion rate in the innermost part of the system. This was followed after a few months by a long-term process, when the brightening of the source was mainly due to a gradual increase in the accretion rate and the emitting area. Our new observations show that the source is currently in a constant plateau phase. We found that the optical spectrum was similar in the first peak and following periods, but around the peak the continuum was bluer and the Hα profile changed significantly between 2012 and 2013. The source was not detected in the millimeter continuum, but we discovered a flattened molecular gas structure with a diameter of 1700 au and mass of 0.3 M⊙ centered on HBC 722. Conclusions: While the first brightness peak might be interpreted as a rapid fall of piled-up material from the inner disk onto the star, the

Collision safety of a hard-shell low-mass vehicle

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaeser, R.; Walz, F.H.; Brunner, A.

1994-06-01

Low-mass vehicles and in particular low-mass electric vehicles as produced today in very small quantities are in general not designed for crashworthiness in collisions. Particular problems of compact low-mass cars are: reduced length of the car front, low mass compared to other vehicles, and heavy batteries in the case of an electric car. With the intention of studying design improvements, three frontal crash tests were run last year: the first one with a commercial, lightweight electric car; the second with a reinforced version of the same car; and the last one with a car based on a different structural designmore » with a `hard-shell` car body. Crash tests showed that the latter solution made better use of the small zone available for continuous energy absorption. The paper discusses further the problem of frontal collisions between vehicles of different weight and, in particular, the side collision. A side-collision test was run with the hard-shell vehicle following the ECE lateral-impact test procedure at 50 km/h and led to results for the EuroSIDI-dummy well below current injury tolerance criteria.« less

Collision safety of a hard-shell low-mass vehicle.

PubMed

Kaeser, R; Walz, F H; Brunner, A

1994-06-01

Low-mass vehicles and in particular low-mass electric vehicles as produced today in very small quantities are in general not designed for crashworthiness in collisions. Particular problems of compact low-mass cars are: reduced length of the car front, low mass compared to other vehicles, and heavy batteries in the case of an electric car. With the intention of studying design improvements, three frontal crash tests were run last year: the first one with a commercial, lightweight electric car; the second with a reinforced version of the same car; and the last one with a car based on a different structural design with a "hard-shell" car body. Crash tests showed that the latter solution made better use of the small zone available for continuous energy absorption. The paper discusses further the problem of frontal collisions between vehicles of different weight and, in particular, the side collision. A side-collision test was run with the hard-shell vehicle following the ECE lateral-impact test procedure at 50 km/h and led to results for the EuroSID1-dummy well below current injury tolerance criteria.

The different baryonic Tully-Fisher relations at low masses.

PubMed

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

2016-06-11

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 V rot . We explore the BTFR when measuring V rot at the flat part of the rotation curve, V flat , at the extent of H i gas, V last , and using 20 per cent ( W 20 ) and 50 per cent ( W 50 ) of the width of H i line profiles. We also compare with the maximum circular velocity of the parent halo, [Formula: see text], within dark matter only simulations. The different BTFRs increasingly diverge as galaxy mass decreases. Using V last  one obtains a power law over four orders of magnitude in baryonic mass, with slope similar to the observed BTFR. Measuring V flat gives similar results as V last 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 V rot to reach a maximum. W 20 gives a similar slope as V last but with slightly lower values of V rot for low-mass galaxies, although this may depend on the extent of the gas in your galaxy sample. W 50 bends away from these other relations towards low velocities at low masses. By contrast, [Formula: see text] bends towards high velocities for low-mass galaxies, as cold gas does not extend out to the radius at which haloes reach [Formula: see text]. Our study highlights the need for careful comparisons between observations and models: one needs to be consistent about the particular method of measuring V rot , and precise about the radius at which velocities are measured.

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.

Optical reading aids for children and young people with low vision.

PubMed

Barker, Lucy; Thomas, Rachel; Rubin, Gary; Dahlmann-Noor, Annegret

2015-03-04

Low vision in childhood is a significant barrier to learning and development, particularly for reading and education. Optical low vision aids may be used to maximise the child's functional vision. The World Health Organization (WHO) has previously highlighted the importance of the use of low vision aids in managing children with visual impairment across the world. To assess the effect of optical low vision aids on reading in children and young people with low vision. We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (2014, Issue 12), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to January 2015), EMBASE (January 1980 to January 2015), the Health Technology Assessment Programme (HTA) (www.hta.ac.uk/), the ISRCTN registry (www.isrctn.com/editAdvancedSearch), ClinicalTrials.gov (www.clinicaltrials.gov) and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic searches for trials. We last searched the electronic databases on 8 January 2015.We also used manual searching to check the references listed in retrieved articles. Manufacturers of low vision aids were contacted to request any information about studies or research regarding their products. We planned to include randomised controlled trials (RCTs) and quasi-RCTs where any optical low vision aid was compared to standard refractive correction in children and young people aged between 5 and 16 years of age with low vision as defined by the WHO. We planned to include within-person design studies where the order of presentation of devices was randomised. Two authors independently reviewed the search results for eligibility . No studies met the inclusion criteria for this review. There is a lack of good quality evidence regarding the use of optical low vision aids in

Optical photometric variable stars towards the Galactic H II region NGC 2282

NASA Astrophysics Data System (ADS)

Dutta, Somnath; Mondal, Soumen; Joshi, Santosh; Jose, Jessy; Das, Ramkrishna; Ghosh, Supriyo

2018-05-01

We report here CCD I-band time series photometry of a young (2-5 Myr) cluster NGC 2282, in order to identify and understand the variability of pre-main-sequence (PMS) stars. The I-band photometry, down to ˜20.5 mag, enables us to probe the variability towards the lower mass end (˜0.1 M⊙) of PMS stars. From the light curves of 1627 stars, we identified 62 new photometric variable candidates. Their association with the region was established from H α emission and infrared (IR) excess. Among 62 variables, 30 young variables exhibit H α emission, near-IR (NIR)/mid-IR (MIR) excess or both and are candidate members of the cluster. Out of 62 variables, 41 are periodic variables, with a rotation rate ranging from 0.2-7 d. The period distribution exhibits a median period at ˜1 d, as in many young clusters (e.g. NGC 2264, ONC, etc.), but it follows a unimodal distribution, unlike others that have bimodality, with slow rotators peaking at ˜6-8 d. To investigate the rotation-disc and variability-disc connection, we derived the NIR excess from Δ(I - K) and the MIR excess from Spitzer [3.6]-[4.5] μm data. No conclusive evidence of slow rotation with the presence of discs around stars and fast rotation for discless stars is obtained from our periodic variables. A clear increasing trend of the variability amplitude with IR excess is found for all variables.

Direct Search for Low Mass Dark Matter Particles with CCDs

DOE PAGES

Barreto, J.; Cease, H.; Diehl, H. T.; ...

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.

Searching for Low-mass Companions of Cepheids, Part II

NASA Astrophysics Data System (ADS)

Remage Evans, Nancy; Tingle, E.; Bond, H. E.; Schaefer, G. H.; Mason, B.; Karovska, M.; Wolk, S.; Pillitteri, I.; DePasquale, J.; Guinan, E.; Engle, S.

2012-01-01

The formation of a binary/multiple system is an effective way to manipulate angular momentum during the star-formation process. The properties of binary systems (separations and mass ratios) are thus the ``fingerprints" of the process. Low mass companions are the most difficult to identify particularly for massive stars. We are conducting a snapshot survey of the nearest Cepheids (5 Msun stars) using the Hubble Space Telescope Wide Field Camera 3 (WFC3) to discover possible resolved low mass companions. The color-magnitude combination is the first approach to identifying probable physical companions. The distributions of mass and separation for these stars will be discussed. Financial suppoet was provided by Hubble grant GO-12215.01-A and the Chandra X-ray Center NASA contract NAS8-03060.

Winds from stripped low-mass helium stars and Wolf-Rayet stars

NASA Astrophysics Data System (ADS)

Vink, Jorick S.

2017-11-01

We present mass-loss predictions from Monte Carlo radiative transfer models for helium (He) stars as a function of stellar mass, down to 2 M⊙. Our study includes both massive Wolf-Rayet (WR) stars and low-mass He stars that have lost their envelope through interaction with a companion. For these low-mass He stars we predict mass-loss rates that are an order of magnitude smaller than by extrapolation of empirical WR mass-loss rates. Our lower mass-loss rates make it harder for these elusive stripped stars to be discovered via line emission, and we should attempt to find these stars through alternative methods instead. Moreover, lower mass-loss rates make it less likely that low-mass He stars provide stripped-envelope supernovae (SNe) of type Ibc. We express our mass-loss predictions as a function of L and Z and not as a function of the He abundance, as we do not consider this physically astute given our earlier work. The exponent of the M⊙ versus Z dependence is found to be 0.61, which is less steep than relationships derived from recent empirical atmospheric modelling. Our shallower exponent will make it more challenging to produce "heavy" black holes of order 40 M⊙, as recently discovered in the gravitational wave event GW 150914, making low metallicity for these types of events even more necessary.

The β Pictoris association low-mass members: Membership assessment, rotation period distribution, and dependence on multiplicity

NASA Astrophysics Data System (ADS)

Messina, S.; Lanzafame, A. C.; Malo, L.; Desidera, S.; Buccino, A.; Zhang, L.; Artemenko, S.; Millward, M.; Hambsch, F.-J.

2017-10-01

Context. Low-mass members of young loose stellar associations and open clusters exhibit a wide spread of rotation periods. Such a spread originates from the distributions of masses and initial rotation periods. However, multiplicity can also play a significant role. Aims: We aim to investigate the role played by physical companions in multiple systems in shortening the primordial disk lifetime, anticipating the rotation spin up with respect to single stars. Methods: We have compiled the most extensive list to date of low-mass bona fide and candidate members of the young 25-Myr β Pictoris association. We have measured from our own photometric time series or from archival time series the rotation periods of almost all members. In a few cases the rotation periods were retrieved from the literature. We used updated UVWXYZ components to assess the membership of the whole stellar sample. Thanks to the known basic properties of most members we built the rotation period distribution distinguishing between bona fide members and candidate members and according to their multiplicity status. Results: We find that single stars and components of multiple systems in wide orbits (>80 AU) have rotation periods that exhibit a well defined sequence arising from mass distribution with some level of spread likely arising from initial rotation period distribution. All components of multiple systems in close orbits (<80 AU) have rotation periods that are significantly shorter than their equal-mass single counterparts. For these close components of multiple systems a linear dependence of rotation rate on separation is only barely detected. A comparison with the younger 13 Myr h Per cluster and with the older 40-Myr open clusters and stellar associations NGC 2547, IC 2391, Argus, and IC 2602 and the 130-Myr Pleiades shows that whereas the evolution of F-G stars is well reproduced by angular momentum evolution models, this is not the case for the slow K and early-M stars. Finally, we find

The Initial Mass Function of the Arches Cluster

NASA Astrophysics Data System (ADS)

Hosek, Matthew; Lu, Jessica; Anderson, Jay; Ghez, Andrea; Morris, Mark; Do, Tuan; Clarkson, William; Albers, Saundra; Weisz, Daniel

2018-01-01

The Arches star cluster is only 26 pc (in projection) from Sgr A*, the supermassive black hole at the Galactic Center. This young massive cluster allows us to examine the impact of the extreme Galactic Center environment on the stellar Initial Mass Function (IMF). However, measuring the IMF of the Arches is challenging due to the highly variable extinction along the line of sight, which makes it difficult to separate cluster members from the field stars. We use high-precision proper motion and photometric measurements obtained with the Hubble Space Telescope to calculate cluster membership probabilities for stars down to ~2 M_sun out to the outskirts of the cluster (3 pc). In addition, we measure the effective temperatures of a small sample of cluster members in order to calibrate the mass-luminosity relationship using using Keck OSIRS K-band spectroscopy. We forward model these observations to simultaneously constrain the cluster IMF, age, distance, and extinction. We obtain an IMF that is shallower than what is observed locally, with a higher fraction of high-mass stars to low mass stars (i.e., “top-heavy”). We will compare the IMF of the Arches to similar clusters in the Galactic disk and quantify the effect of the GC environment on the star formation process.

SHIELD: EVLA HI Spectral Line Observations of Low-mass Dwarfs

NASA Astrophysics Data System (ADS)

Miazzo, Masao; Ruvolo, Elizabeth; Cannon, John M.; McNichols, Andrew; Teich, Yaron; Adams, Elizabeth A.; Giovanelli, Riccardo; Haynes, Martha P.; McQuinn, Kristen B.; Salzer, John Joseph; Skillman, Evan D.; Dolphin, Andrew E.; Elson, Edward C.; Haurberg, Nathalie C.; Huang, Shan; Janowiecki, Steven; Jozsa, Gyula; Leisman, Luke; Ott, Juergen; Papastergis, Emmanouil; Rhode, Katherine L.; Saintonge, Amelie; Van Sistine, Angela; Warren, Steven R.

2017-01-01

The “Survey of HI in Extremely Low-mass Dwarfs” (SHIELD) is a multiwavelength study of local volume low-mass galaxies. Using the now-complete Arecibo Legacy Fast ALFA (ALFALFA) source catalog, 82 systems are identified that meet distance, line width, and HI flux criteria for being gas-rich, low-mass galaxies. These systems harbor neutral gas reservoirs smaller than 3x10^7 M_sun, thus populating the faint end of the HI mass function with statistical confidence for the first time. Here we present new Karl G. Jansky Very Large Array D-configuration HI spectral line observations of 32 previously unobserved galaxies. These low angular resolution (~40" beam) images localize the HI gas; with a few exceptions, the HI gas is co-spatial with the optical centers of the galaxies. These images provide the first glimpse of the neutral interstellar medium in these systems.Support for this work was provided by NSF grant 1211683 to JMC at Macalester College.

Eclipse timings of the low-mass X-ray binary EXO 0748-676: Statistical arguments against orbital period changes

NASA Technical Reports Server (NTRS)

Hertz, Paul; Wood, Kent S.; Cominsky, Lynn

1995-01-01

EXO 0748-676, an eclipsing low-mass X-ray binary, is one of only about four or five low-mass X-ray binaries for which orbital period evolution has been reported. We observed a single eclipse egress with ROSAT . The time of this egress is consistent with the apparent increase in P(sub orb) previously reported on the basis of EXOSAT and Ginga observations. Standard analysis, in which O-C (observed minus calculated) timing residuals are examined for deviations from a constant period, implicitly assume that the only uncertainty in each residual is measurement error and that these errors are independent. We argue that the variable eclipse durations and profiles observed in EXO 0748-676 imply that there is an additional source of uncertainty in timing measurements, that this uncertainty is intrinsic to the binary system, and that it is correlated from observation to observation with a variance which increases as a function of the number of binary cycles between observations. This intrinsic variability gives rise to spurious trends in O-C residuals which are misinterpreted as changes in the orbital period. We describe several statistics tests which can be used to test for the presence of intrinsic variability. We apply those statistical tests which are suitable to the EXO 0748-676 observations. The apparent changes in the orbital period of EXO 0748-676 can be completely accounted for by intrinsic variability with an rms variability of approximately 0.35 s per orbital cycle. The variability appears to be correlated from cycle-to-cycle on timescales of less than 1 yr. We suggest that the intrinsic variability is related to slow changes in either the source's X-ray luminosity or the structure of the companion star's atmosphere. We note that several other X-ray binaries and cataclysmic variables have previously reported orbital period changes which may also be due to intrinsic variability rather than orbital period evolution.

LEO P: AN UNQUENCHED VERY LOW-MASS GALAXY

DOE Office of Scientific and Technical Information (OSTI.GOV)

McQuinn, Kristen B. W.; Skillman, Evan D.; Berg, Danielle

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 10more » 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{sub ⊙}. 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{sup −5} M{sub ⊙} yr{sup −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.« less

Discovery of wide low and very low-mass binary systems using Virtual Observatory tools

NASA Astrophysics Data System (ADS)

Gálvez-Ortiz, M. C.; Solano, E.; Lodieu, N.; Aberasturi, M.

2017-04-01

The frequency of multiple systems and their properties are key constraints of stellar formation and evolution. Formation mechanisms of very low-mass (VLM) objects are still under considerable debate, and an accurate assessment of their multiplicity and orbital properties is essential for constraining current theoretical models. Taking advantage of the virtual observatory capabilities, we looked for comoving low and VLM binary (or multiple) systems using the Large Area Survey of the UKIDSS LAS DR10, SDSS DR9 and the 2MASS Catalogues. Other catalogues (WISE, GLIMPSE, SuperCosmos, etc.) were used to derive the physical parameters of the systems. We report the identification of 36 low and VLM (˜M0-L0 spectral types) candidates to binary/multiple system (separations between 200 and 92 000 au), whose physical association is confirmed through common proper motion, distance and low probability of chance alignment. This new system list notably increases the previous sampling in their mass-separation parameter space (˜100). We have also found 50 low-mass objects that we can classify as ˜L0-T2 according to their photometric information. Only one of these objects presents a common proper motion high-mass companion. Although we could not constrain the age of the majority of the candidates, probably most of them are still bound except four that may be under disruption processes. We suggest that our sample could be divided in two populations: one tightly bound wide VLM systems that are expected to last more than 10 Gyr, and other formed by weak bound wide VLM systems that will dissipate within a few Gyr.

NIR integral field spectroscopy of high mass young stellar objects

NASA Astrophysics Data System (ADS)

Murakawa, K.; Lumsden, S. L.; Oudmaijer, R. D.; Davies, B.; Hoare, M. G.

2013-03-01

We present K-band Integral Field Spectroscopy of six high mass young stellar objects (IRAS~18151-1208, AFGL~2136, S106~IRS4, V645 Cyg, IRAS~19065+0526, and G082.5682+ 00.4040) obtained using the adaptive optics assisted NIFS instrument mounted on the Gemini North telescope. The targets are chosen from the Red MSX Source survey led by University of Leeds. The data show the spectral features of Brγ, H2, and gas phase CO emissions and absorptions with a spectral resolution of R ≈ 5500, which allow a three-dimensional spectro-astrometric analysis of the line emissions. We discuss the results of the ionized jets and winds, and rotating CO torus.

Seasonal to Mesoscale Variability of Water Masses in Barrow Canyon,Chukchi Sea

NASA Astrophysics Data System (ADS)

Nobre, C.; Pickart, R. S.; Moore, K.; Ashjian, C. J.; Arrigo, K. R.; Grebmeier, J. M.; Vagle, S.; Itoh, M.; Berchok, C.; Stabeno, P. J.; Kikuchi, T.; Cooper, L. W.; Hartwell, I.; He, J.

2016-02-01

Barrow Canyon is one of the primary conduits by which Pacific-origin water exits the Chukchi Sea into the Canada Basin. As such, it is an ideal location to monitor the different water masses through the year. At the same time, the canyon is an energetic environment where mixing and entrainment can occur, modifying the pacific-origin waters. As part of the Distributed Biological Observatory (DBO) program, a transect across the canyon was occupied 24 times between 2010-2013 by international ships of opportunity passing through the region during summer and early-fall. Here we present results from an analysis of these sections to determine the seasonal evolution of the water masses and to investigate the nature of the mesoscale variability. The mean state shows the clear presence of six water masses present at various times through the summer. The seasonal evolution of these summer water masses is characterized both in depth space and in temperature-salinity (T-S) space. Clear patterns emerge, including the arrival of Alaskan coastal water and its modification in early-fall. The primary mesoscale variability is associated with wind-driven upwelling events which occur predominantly in September. The atmospheric forcing of these events is investigated as is the oceanic response.

Body Mass, Total Body Fat Percentage, and Visceral Fat Level Predict Insulin Resistance Better Than Waist Circumference and Body Mass Index in Healthy Young Male Adults in Indonesia.

PubMed

Kurniawan, Liong Boy; Bahrun, Uleng; Hatta, Mochammad; Arif, Mansyur

2018-05-01

The incidence of obesity which leads to insulin resistance (IR) and metabolic disorder is increasing in developing countries, including Indonesia. Male adults have a higher risk of abdominal obesity than females. This is associated with cardiometabolic disorders. Several anthropometric measurements have been proposed to predict IR. The aim of this study was to investigate whether body mass, body mass index (BMI), waist circumference (WC), body fat percentage (BF) or visceral fat level (VF) could become a better predictor of IR in healthy young male adults. A total of 140 healthy young male adults ranging from 18⁻25 years were recruited in the study. Insulin resistance was measured by calculating their Homeostatic Model Assessment for Insulin Resistance (HOMA-IR). Subjects with a HOMA-IR value ≥75th percentile, with cut off 3.75, were defined as IR. Anthropometric measurements including body weight, BMI, and WC were performed, whereas BF and VC were measured using bioelectrical impedance analysis (BIA). IR had a strong correlation with body weight, BMI, WC, BF, and VF. In the area under the curve of body mass, BF and VF were slightly greater than WC and BMI. Anthropometric measurements correlated strongly with IR but body weight, BF, VF had a stronger correlation than WC and BMI in healthy young male adults.

School burnout and heart rate variability: risk of cardiovascular disease and hypertension in young adult females.

PubMed

May, Ross W; Seibert, Gregory S; Sanchez-Gonzalez, Marcos A; Fincham, Frank D

2018-05-01

Emerging research documents the relationship between school burnout and some indicators of increased cardiovascular risk. Indicators of cardiovascular functioning assessed via ambulatory blood pressure and heart rate variability (HRV) have not been thoroughly explored in this research domain. Therefore, the current study examined relationships between school burnout and indicators of cardiac functioning via 24 h ambulatory blood pressure (BP) and electrocardiogram monitoring in a sample of young adult female undergraduates (N = 88). Two hypotheses were tested: (1) that independent of related negative affective symptomology (depression and anxiety), increased school burnout would be related to greater systolic and diastolic BP, higher low frequency (LF) HRV and lower very low frequency (VLF) HRV, and (2) that lower VLF would be related to greater school burnout independently of LF HRV. Hierarchical multiple regression analyzes showed that school burnout was significantly related to elevated ambulatory BP (systolic and diastolic) and HRV markers of increased cardiac sympathovagal tone. These findings support the hypotheses and suggest that school burnout might be implicated in the development of pre-hypertension or early cardiovascular disease. Study limitations and the need for future longitudinal research are discussed.

Lack of Association of Estrogen Receptor Alpha Gene Polymorphisms with Cardiorespiratory and Metabolic Variables in Young Women

PubMed Central

Rebelo, Ana Cristina; Verlengia, Rozangela; Kunz, Vandeni; Tamburus, Nayara; Cerda, Alvaro; Hirata, Rosario; Hirata, Mario; Silva, Ester

2012-01-01

This study examined the association of estrogen receptor alpha gene (ESR1) polymorphisms with cardiorespiratory and metabolic parameters in young women. In total, 354 healthy women were selected for cardiopulmonary exercise testing and short-term heart rate (HR) variability (HRV) evaluation. The HRV analysis was determined by the temporal indices rMSSD (square root of the mean squared differences of successive R–R intervals (RRi) divided by the number of RRi minus one), SDNN (root mean square of differences from mean RRi, divided by the number of RRi) and power spectrum components by low frequency (LF), high frequency (HF) and LF/HF ratio. Blood samples were obtained for serum lipids, estradiol and DNA extraction. ESR1 rs2234693 and rs9340799 polymorphisms were analyzed by PCR and fragment restriction analysis. HR and oxygen uptake (VO2) values did not differ between the ESR1 polymorphisms with respect to autonomic modulation. We not find a relationship between ESR1 T–A, T–G, C–A and C–G haplotypes and cardiorespiratory and metabolic variables. Multiple linear regression analysis demonstrated that VO2, total cholesterol and triglycerides influence HRV (p < 0.05). The results suggest that ESR1 variants have no effect on cardiorespiratory and metabolic variables, while HRV indices are influenced by aerobic capacity and lipids in healthy women. PMID:23202974

Low Mass AGN: Combining IRAC With Near-IR Grism Spectroscopy

NASA Astrophysics Data System (ADS)

Colbert, James; Teplitz, Harry; Malkan, Matt; Scarlata, Claudia; Bagley, Micaela; Baronchelli, Ivano; Hayden-Pawson, Connor; Rafelski, Marc

2017-10-01

Low mass AGN are critical to understanding the evolution of AGNs and stars in galaxies, marking the time periods of highest accretion efficiency and greatest likely deviations from the black hole mass - sigma correlation. Using the WFC3 Infrared Spectroscopic Parallels (WISP), we have just recently identified 68 candidate z > 1 AGN in 27 fields from their near-infrared emission line ratios. The WISP survey selects emission line galaxies without any pre-selection bias and is exquisitely sensitive to low mass (down to 10^7 solar masses), high-equivalent width galaxies that are missed by most other surveys. We propose to take IRAC 4.5 micron imaging of these AGN candidate fields in order to confirm 68 low mass AGN candidates, identify additional low mass IR-AGN missed by emission line selection, and produce the SED fits that can separate hot dust from star light, allowing comparison of stellar mass to AGN bolometric luminosity. The upcoming Euclid and WFIRST missions will generate hundreds of thousands of near-infrared spectra over a similar redshift range to WISP. For most of these objects, near-infrared emission line ratios will be the only viable AGN diagnostic. The Spitzer IRAC color AGN selection is one of the most robust AGN identifiers available. We wish to test these near-infrared emission line selection methods against the IRAC selection in order to evaluate the reliability of the AGN these future missions are likely to produce.

Body Mass, Training, Menses, and Bone in Adolescent Runners: A 3-y Follow-Up

USDA-ARS?s Scientific Manuscript database

Abstract: Endurance runners with low bone mass during adolescence may be at risk of developing a low peak bone mineral density (BMD) as a young adult. However, it is possible that they mature late and undergo delayed bone mass accumulation. PURPOSE: We evaluated 40 adolescent runners (age 15.9 ± 0....

Demonstration of a Variable Phase Turbine Power System for Low Temperature Geothermal Resources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hays, Lance G

2014-07-07

A variable phase turbine assembly will be designed and manufactured having a turbine, operable with transcritical, two-phase or vapor flow, and a generator – on the same shaft supported by process lubricated bearings. The assembly will be hermetically sealed and the generator cooled by the refrigerant. A compact plate-fin heat exchanger or tube and shell heat exchanger will be used to transfer heat from the geothermal fluid to the refrigerant. The demonstration turbine will be operated separately with two-phase flow and with vapor flow to demonstrate performance and applicability to the entire range of low temperature geothermal resources. The vapormore » leaving the turbine is condensed in a plate-fin refrigerant condenser. The heat exchanger, variable phase turbine assembly and condenser are all mounted on single skids to enable factory assembly and checkout and minimize installation costs. The system will be demonstrated using low temperature (237F) well flow from an existing large geothermal field. The net power generated, 1 megawatt, will be fed into the existing power system at the demonstration site. The system will demonstrate reliable generation of inexpensive power from low temperature resources. The system will be designed for mass manufacturing and factory assembly and should cost less than $1,200/kWe installed, when manufactured in large quantities. The estimated cost of power for 300F resources is predicted to be less than 5 cents/kWh. This should enable a substantial increase in power generated from low temperature geothermal resources.« less

Association between subjective actual sleep duration, subjective sleep need, age, body mass index, and gender in a large sample of young adults.

PubMed

Kalak, Nadeem; Brand, Serge; Beck, Johannes; Holsboer-Trachsler, Edith; Wollmer, M Axel

2015-01-01

Poor sleep is a major health concern, and there is evidence that young adults are at increased risk of suffering from poor sleep. There is also evidence that sleep duration can vary as a function of gender and body mass index (BMI). We sought to replicate these findings in a large sample of young adults, and also tested the hypothesis that a smaller gap between subjective sleep duration and subjective sleep need is associated with a greater feeling of being restored. A total of 2,929 university students (mean age 23.24±3.13 years, 69.1% female) took part in an Internet-based survey. They answered questions related to demographics and subjective sleep patterns. We found no gender differences in subjective sleep duration, subjective sleep need, BMI, age, or feeling of being restored. Nonlinear associations were observed between subjective sleep duration, BMI, and feeling of being restored. Moreover, a larger discrepancy between subjective actual sleep duration and subjective sleep need was associated with a lower feeling of being restored. The present pattern of results from a large sample of young adults suggests that males and females do not differ with respect to subjective sleep duration, BMI, or feeling of being restored. Moreover, nonlinear correlations seemed to provide a more accurate reflection of the relationship between subjective sleep and demographic variables.

Calorimetry of low mass Pu239 items

DOE Office of Scientific and Technical Information (OSTI.GOV)

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.

Properties of Low-mass AGN as They Relate to Unification and Massive AGN

NASA Astrophysics Data System (ADS)

Hood, Carol E.

2011-01-01

Current unification models of AGN suggest the observational differences between Type 1 and Type 2 objects are solely due to the orientation angle of the object. Observations have proved consistent with predictions and continue to strengthen the case for unification, however, many are still searching for "true" Type 2 objects, including predictions of their formation due to low luminosity or low accretion rate. Low-mass (< 106solar masses) AGN provide interesting environments in which these unification models can be studied. We also aim to compare the properties of low-mass AGN with their more massive counterparts to look for structural similarities and differences over a more substantial range of luminosities and accretion rates than previously studied. We present an in-depth multi-wavelength study of one of the prototypical low-mass AGN, POX 52, investigating the properties of the central engine along with that of the host galaxy. This includes data from the VLA, Spitzer, 2MASS, HST, GALEX, XMM, and Chandra, providing us with one of the most comprehensive looks into low-mass AGN. Unlike the other prototypical low-mass AGN, NGC 4395, POX 52 resides in a dwarf elliptical galaxy, accreting at ≈ 0.35 the Eddington limit. Additionally, we examine a sample 41 Type 1 and Type 2 objects, including POX 52 and NGC 4395, with the Spitzer IRS and a sub-sample of those with XMM to study the absorption properties of low-mass AGN, to test the validity of unification models in the low-mass regime, and to investigate possible structural differences between objects with low and high mass black holes and accretion rates. We will discuss the IR spectral shape and present emission-line diagnostics for Type 1 and Type 2 AGNs at low masses.

A low muscle mass increases mortality in compensated cirrhotic patients with sepsis.

PubMed

Lucidi, Cristina; Lattanzi, Barbara; Di Gregorio, Vincenza; Incicco, Simone; D'Ambrosio, Daria; Venditti, Mario; Riggio, Oliviero; Merli, Manuela

2018-05-01

Severe infections and muscle wasting are both associated to poor outcome in cirrhosis. A possible synergic effect of these two entities in cirrhotic patients has not been previously investigated. We aimed at analysing if a low muscle mass may deteriorate the outcome of cirrhotic patients with sepsis. Consecutive cirrhotic patients hospitalized for sepsis were enrolled in the study. Patients were classified for the severity of liver impairment (Child-Pugh class) and for the presence of "low muscle mass" (mid-arm muscle circumference<5th percentile). The development of complication during hospitalization and survival was analysed. There were 74 consecutive cirrhotics with sepsis. Forty-three of these patients showed low muscle mass. In patients with and without low muscle mass, severity of liver disease and characteristics of infections were similar. Mortality tended to be higher in patients with low muscle mass (47% vs 26%, P = .06). A multivariate analysis selected low muscle mass (P < .01, HR: 3.2, IC: 1.4-4.8) and Child-Pugh C (P < .01, HR: 3.3, 95% IC: 1.5-4.9) as independent predictors of in-hospital mortality. In Child-Pugh A-B patients, mortality was higher in patients with low muscle mass compared with those without (50% vs 16%; P = .01). The mortality rate and the incidence of complications in malnourished patients classified in Child-Pugh A-B were similar to those Child-Pugh C. Low muscle mass worsen prognosis in cirrhotic patients with severe infections. This is particularly evident in patients with Child A-B cirrhosis in whom the coexistence of low muscle mass and sepsis caused a negative impact on mortality similar to that observable in all Child C patients with sepsis. © 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Disambiguating seesaw models using invariant mass variables at hadron colliders

DOE PAGES

Dev, P. S. Bhupal; Kim, Doojin; Mohapatra, Rabindra N.

2016-01-19

Here, we propose ways to distinguish between different mechanisms behind the collider signals of TeV-scale seesaw models for neutrino masses using kinematic endpoints of invariant mass variables. We particularly focus on two classes of such models widely discussed in literature: (i) Standard Model extended by the addition of singlet neutrinos and (ii) Left-Right Symmetric Models. Relevant scenarios involving the same "smoking-gun" collider signature of dilepton plus dijet with no missing transverse energy differ from one another by their event topology, resulting in distinctive relationships among the kinematic endpoints to be used for discerning them at hadron colliders. Furthermore, these kinematic endpoints are readily translated to the mass parameters of the on-shell particles through simple analytic expressions which can be used for measuring the masses of the new particles. We also conducted a Monte Carlo simulation with detector effects in order to test the viability of the proposed strategy in a realistic environment. Finally, we discuss the future prospects of testing these scenarios at themore » $$\\sqrt{s}$$ = 14 and 100TeV hadron colliders.« less

Disambiguating seesaw models using invariant mass variables at hadron colliders

NASA Astrophysics Data System (ADS)

Dev, P. S. Bhupal; Kim, Doojin; Mohapatra, Rabindra N.

2016-01-01

We propose ways to distinguish between different mechanisms behind the collider signals of TeV-scale seesaw models for neutrino masses using kinematic endpoints of invariant mass variables. We particularly focus on two classes of such models widely discussed in literature: (i) Standard Model extended by the addition of singlet neutrinos and (ii) Left-Right Symmetric Models. Relevant scenarios involving the same "smoking-gun" collider signature of dilepton plus dijet with no missing transverse energy differ from one another by their event topology, resulting in distinctive relationships among the kinematic endpoints to be used for discerning them at hadron colliders. These kinematic endpoints are readily translated to the mass parameters of the on-shell particles through simple analytic expressions which can be used for measuring the masses of the new particles. A Monte Carlo simulation with detector effects is conducted to test the viability of the proposed strategy in a realistic environment. Finally, we discuss the future prospects of testing these scenarios at the √{s}=14 and 100 TeV hadron colliders.

X-shooter study of accretion in Chamaeleon I. II. A steeper increase of accretion with stellar mass for very low-mass stars?

NASA Astrophysics Data System (ADS)

Manara, C. F.; Testi, L.; Herczeg, G. J.; Pascucci, I.; Alcalá, J. M.; Natta, A.; Antoniucci, S.; Fedele, D.; Mulders, G. D.; Henning, T.; Mohanty, S.; Prusti, T.; Rigliaco, E.

2017-08-01

The dependence of the mass accretion rate on the stellar properties is a key constraint for star formation and disk evolution studies. Here we present a study of a sample of stars in the Chamaeleon I star-forming region carried out using spectra taken with the ESO VLT/X-shooter spectrograph. The sample is nearly complete down to stellar masses (M⋆) 0.1 M⊙ for the young stars still harboring a disk in this region. We derive the stellar and accretion parameters using a self-consistent method to fit the broadband flux-calibrated medium resolution spectrum. The correlation between accretion luminosity to stellar luminosity, and of mass accretion rate to stellar mass in the logarithmic plane yields slopes of 1.9 ± 0.1 and 2.3 ± 0.3, respectively. These slopes and the accretion rates are consistent with previous results in various star-forming regions and with different theoretical frameworks. However, we find that a broken power-law fit, with a steeper slope for stellar luminosity lower than 0.45 L⊙ and for stellar masses lower than 0.3 M⊙ is slightly preferred according to different statistical tests, but the single power-law model is not excluded. The steeper relation for lower mass stars can be interpreted as a faster evolution in the past for accretion in disks around these objects, or as different accretion regimes in different stellar mass ranges. Finally, we find two regions on the mass accretion versus stellar mass plane that are empty of objects: one region at high mass accretion rates and low stellar masses, which is related to the steeper dependence of the two parameters we derived. The second region is located just above the observational limits imposed by chromospheric emission, at M⋆ 0.3 - 0.4 M⊙. These are typical masses where photoevaporation is known to be effective. The mass accretion rates of this region are 10-10M⊙/yr, which is compatible with the value expected for photoevaporation to rapidly dissipate the inner disk. This work is

Motivations for Sex among Low-Income African American Young Women

ERIC Educational Resources Information Center

Deardorff, Julianna; Suleiman, Ahna Ballonoff; Dal Santo, Teresa S.; Flythe, Michelle; Gurdin, J. Barry; Eyre, Stephen L.

2013-01-01

African American young women exhibit higher risk for sexually transmitted infections, including HIV/AIDS, compared with European American women, and this is particularly true for African American women living in low-income contexts. We used rigorous qualitative methods, that is, domain analysis, including free listing ("n" = 20),…

Reconnaissance of Young M Dwarfs: Locating the Elusive Majority of Nearby Moving Groups

NASA Astrophysics Data System (ADS)

Bowler, Brendan; Liu, Michael; Riaz, Basmah; Gizis, John; Shkolnik, Evgenya

2014-02-01

With ages between ~8-120 Myr and distances ≲80 pc, young moving group members make excellent targets for detailed studies of pre-main sequence evolution and exoplanet imaging surveys. We propose to finish a low-resolution spectroscopic program started in 2013B to confirm our sample of ~1300 X-ray-selected active M dwarfs, about one-third of which are expected to be members of young moving groups. Our larger program consists of three parts: an initial reconnaissance phase of low-resolution spectroscopy to vet unlikely association members, radial velocity observations to confirm group membership, and deep adaptive optics imaging to study the architecture and demographics of giant planets around low-mass stars. Our observations in 2014A will finish the phase of low-resolution spectroscopy covering the second half of the sky. We will also exploit our rich sample to study the evolution of chromospheric and coronal activity in low-mass stars with unprecedented precision. Altogether, this program will roughly double the population of M dwarfs in young moving groups, providing new targets for a broad range of star and planet formation studies in the near-future.

Material variability as measured by low temperature electrical resistivity.

NASA Technical Reports Server (NTRS)

Clark, A. F.; Tryon, P. V.

1972-01-01

Low temperature electrical resistivity was used to determine the material variability (1) between different manufacturers, (2) between different heats from the same manufacturer, and (3) within a given heat for Al 2024, Al-5% Mg alloys, Inconel 718, A286 stainless, and AISI 316. Generally, the coefficient of variation for solution annealed alloys ranged from 1.2 to 14% between manufacturers, 0.8 to 5.1% between heats, and 0.1 to 1.6% within a heat with stainless steels at the low ends and Al 2024 at the high ends. The variability is increased if the material is in a precipitation-hardened condition. A statistical analysis suggests that the variability within a heat is non-normal.

Wind properties of variable B supergiants. Evidence of pulsations connected with mass-loss episodes

NASA Astrophysics Data System (ADS)

Haucke, M.; Cidale, L. S.; Venero, R. O. J.; Curé, M.; Kraus, M.; Kanaan, S.; Arcos, C.

2018-06-01

Context. Variable B supergiants (BSGs) constitute a heterogeneous group of stars with complex photometric and spectroscopic behaviours. They exhibit mass-loss variations and experience different types of oscillation modes, and there is growing evidence that variable stellar winds and photospheric pulsations are closely related. Aims: To discuss the wind properties and variability of evolved B-type stars, we derive new stellar and wind parameters for a sample of 19 Galactic BSGs by fitting theoretical line profiles of H, He, and Si to the observed ones and compare them with previous determinations. Methods: The synthetic line profiles are computed with the non-local thermodynamic equilibrium (NLTE) atmosphere code FASTWIND, with a β-law for hydrodynamics. Results: The mass-loss rate of three stars has been obtained for the first time. The global properties of stellar winds of mid/late B supergiants are well represented by a β-law with β > 2. All stars follow the known empirical wind momentum-luminosity relationships, and the late BSGs show the trend of the mid BSGs. HD 75149 and HD 99953 display significant changes in the shape and intensity of the Hα line (from a pure absorption to a P Cygni profile, and vice versa). These stars have mass-loss variations of almost a factor of 2.8. A comparison among mass-loss rates from the literature reveals discrepancies of a factor of 1 to 7. This large variation is a consequence of the uncertainties in the determination of the stellar radius. Therefore, for a reliable comparison of these values we used the invariant parameter Qr. Based on this parameter, we find an empirical relationship that associates the amplitude of mass-loss variations with photometric/spectroscopic variability on timescales of tens of days. We find that stars located on the cool side of the bi-stability jump show a decrease in the ratio V∞/Vesc, while their corresponding mass-loss rates are similar to or lower than the values found for stars on the

Physical activity and dark skin tone: protective factors against low bone mass in Mexican men.

PubMed

Vivanco-Muñoz, Nalleli; Jo, Talavera; Gerardo, Huitron-Bravo; Juan, Tamayo; Clark, Patricia

2012-01-01

A cross-sectional study was conducted on 268 Mexican men between the ages of 13 and 80 yr to evaluate the association of clinical factors related with bone mass. Men from high schools, universities, and retirement homes were invited to participate. Body mass index (BMI) was measured, and bone mineral density (BMD) was assessed using dual-energy X-ray absorptiometry for L1-L4 and total hip. Factors related to bone mass were assessed by questionnaire and analyzed using a logistic regression model. Demographic factors (age, education, and occupation), clinical data (BMI, skin tone, previous fracture, history of osteoporosis [OP], and history of fractures), and lifestyle variables (diet, physical activity, sun exposure, and smoking) were evaluated. Physical activity (≥ 60 min/5 times a week) reduced the risk for low BMD for age, osteopenia, and OP at the spine and total hip (odds ratio [OR]: 0.276; 95% confidence interval [CI]: 0.099-0.769; p=0.014; and OR: 0.184; 95% CI: 0.04-0.849; p=0.03, respectively). Dark skin tone was a protective factor, decreasing the risk by up to 70%. In this population of healthy Mexican men (aged 13-80 yr), dark skin and physical activity were protective factors against low bone mass. Copyright © 2012 The International Society for Clinical Densitometry. Published by Elsevier Inc. All rights reserved.

Characterizing Protoplanetary Disks in a Young Binary in Orion

NASA Astrophysics Data System (ADS)

Powell, Jonas; Hughes, A. Meredith; Mann, Rita; Flaherty, Kevin; Di Francesco, James; Williams, Jonathan

2018-01-01

Planetary systems form in circumstellar disks of gas and dust surrounding young stars. One open question in the study of planet formation involves understanding how different environments affect the properties of the disks and planets they generate. Understanding the properties of disks in high-mass star forming regions (SFRs) is critical since most stars - probably including our Sun - form in those regions. By comparing the disks in high-mass SFRs to those in better-studied low-mass SFRs we can learn about the role environment plays in planet formation. Here we present 0.5" resolution observations of the young two-disk binary system V2434 Ori in the Orion Nebula from the Atacama Large Millimeter/submillimeter Array (ALMA) in molecular line tracers of CO(3-2), HCN(4-3), HCO+(4-3) and CS(7-6). We model each disk’s mass, radius, temperature structure, and molecular abundances, by creating synthetic images using an LTE ray-tracing code and comparing simulated observations with the ALMA data in the visibility domain. We then compare our results to a previous study of molecular line emission from a single Orion proplyd, modeled using similar methods, and to previously characterized disks in low-mass SFRs to investigate the role of environment in disk chemistry and planetary system formation.

Bone mass and lifestyle related factors: a comparative study between Japanese and Inner Mongolian young premenopausal women.

PubMed

Zhang, M; Shimmura, T; Bi, L F; Nagase, H; Nishino, H; Kajita, E; Eto, M; Wang, H B; Su, X L; Chang, H; Aratani, T; Kagamimori, S

2004-07-01

The purpose of this study was to evaluate the ethnic difference in bone mass between Japanese and Inner Mongolian young premenopausal women and to assess the contribution of lifestyle related and anthropometric factors to bone mass. We studied 33 Japanese and 44 Inner Mongolian healthy young women, aged 20-34 years, in urban area. Speed of sound (SOS), broadband ultrasound attenuation (BUA) and stiffness index (SI) were measured at the calcaneus using quantitative ultrasound (QUS) analysis. Age at menarche, regularity of menstruation and lifestyle related factors were estimated by a self-reported questionnaire. There were no differences between the two groups in age, height, weight, BMI, regularity of menstruation, frequency of meat intake, frequency of yellow-green vegetable intake and exercise habit. Japanese women had significantly lower age at menarche and higher proportion of milk consumption habit at junior high school, senior school and present. Before adjustment, Japanese women had significantly higher SOS and SI than Inner Mongolian women. However, after adjustment for age at menarche and milk consumption habit at junior high school, both of which were significantly different between groups, no group-differences remained in either SOS or SI. These results suggest that the differences in age at menarche and milk consumption habit at junior high school, which relate to hormonal and nutritional status during puberty, may account for the differences in bone mass between Japanese and Inner Mongolian young women.

Physiological and subjective responses to low relative humidity in young and elderly men.

PubMed

Sunwoo, Yujin; Chou, Chinmei; Takeshita, Junko; Murakami, Motoko; Tochihara, Yutaka

2006-05-01

In order to compare the physiological and the subjective responses to low relative humidity of elderly and young men, we measured saccharin clearance time (SCT), frequency of blinking, hydration state of the skin, transepidermal water loss (TEWL), sebum level recovery and skin temperatures as physiological responses. We asked subjects to evaluate thermal, dryness and comfort sensations as subjective responses using a rating scale. Eight non-smoking healthy male students (21.7+/-0.8 yr) and eight non-smoking healthy elderly men (71.1+/-4.1 yr) were selected. The pre-room conditions were maintained at an air temperature (Ta) of 25 degrees C and a relative humidity (RH) of 50%. The test-room conditions were adjusted to provide 25 degrees C Ta and RH levels of 10%, 30% and 50%. RH had no effect on the activity of the sebaceous gland or change of mean skin temperature. SCT of the elderly group under 10% RH was significantly longer than that of the young group. In particular, considering the SCT change, the nasal mucous membrane seems to be affected more in the elderly than in the young in low RH. Under 30% RH, the eyes and skin become dry, and under 10% RH the nasal mucous membrane becomes dry as well as the eyes and skin. These findings suggested that to avoid dryness of the eyes and skin, it is necessary to maintain greater than 30% RH, and to avoid dryness of the nasal mucous membrane, it is necessary to maintain greater than 10% RH. On the thermal sensation of the legs, at the lower humidity level, the elderly group felt cooler than the young group. On the dry sensation of the eyes and throat, the young group felt drier than the elderly group at the lower humidity levels. From the above results, the elderly group had difficulty in feeling dryness in the nasal mucous membrane despite being easily affected by low humidity. On the other hand, the young group felt the change of humidity sensitively despite not being severely affected by low humidity. Ocular mucosa and

Biocompatible low Young's modulus achieved by strong crystallographic elastic anisotropy in Ti-15Mo-5Zr-3Al alloy single crystal.

PubMed

Lee, S-H; Todai, M; Tane, M; Hagihara, K; Nakajima, H; Nakano, T

2012-10-01

The elastic anisotropy of the Ti-15Mo-5Zr-3Al (mass%) β-Ti alloy, an ISO certified biomedical material, was investigated using its single crystal. It was revealed that the Young's modulus exhibited pronounced anisotropy. The Young's modulus was reduced to 44.4GPa along the 〈100〉 direction in the Ti-15Mo-5Zr-3Al single crystal, that is comparable to that of human cortical bones. We determined the strategy that β-Ti alloys with extremely low moduli can be developed by reducing the electron-atom (e/a) ratio in alloys, and by suppressing the formation of the ω-phase at the same time. This new knowledge must lead to the development of "single crystalline β-Ti implant materials" as hard tissue replacements for reducing the stress shielding effect. Copyright © 2012 Elsevier Ltd. All rights reserved.

Photometric detection of a candidate low-mass giant binary system at the Milky Way Galactic Center

NASA Astrophysics Data System (ADS)

Krishna Gautam, Abhimat; Do, Tuan; Ghez, Andrea; Sakai, Shoko; Morris, Mark; Lu, Jessica; Witzel, Gunther; Jia, Siyao; Becklin, Eric Eric; Matthews, Keith

2018-01-01

We present the discovery of a new periodic variable star at the Milky Way Galactic Center (GC). This study uses laser guide-star adaptive optics data collected with the W. M. Keck 10 m telescope in the K‧-band (2.2 µm) over 35 nights spanning an 11 year time baseline, and 5 nights of additional H-band (1.6 µm) data. We implemented an iterative photometric calibration and local correction technique, resulting in a photometric uncertainty of Δm_K‧ ∼ 0.03 to a magnitude of m_K‧ ∼ 16.The periodically variable star has a 39.42 day period. We find that the star is not consistent with known periodically variable star classes in this period range with its observed color and luminosity, nor with an eclipsing binary system. The star's color and luminosity are however consistent with an ellipsoidal binary system at the GC, consisting of a K-giant and a dwarf component with an orbital period of 78.84 days. If a binary system, it represents the first detection of a low-mass giant binary system in the central half parsec of the GC. Such long-period binary systems can easily evaporate in the dense environment of the GC due to interactions with other stars. The existence and properties of a low-mass, long-period binary system can thus place valuable constraints on dynamical models of the GC environment and probe the density of the hypothesized dark cusp of stellar remnants at the GC.

Variable mass pendulum behaviour processed by wavelet analysis

NASA Astrophysics Data System (ADS)

Caccamo, M. T.; Magazù, S.

2017-01-01

The present work highlights how, in order to characterize the motion of a variable mass pendulum, wavelet analysis can be an effective tool in furnishing information on the time evolution of the oscillation spectral content. In particular, the wavelet transform is applied to process the motion of a hung funnel that loses fine sand at an exponential rate; it is shown how, in contrast to the Fourier transform which furnishes only an average frequency value for the motion, the wavelet approach makes it possible to perform a joint time-frequency analysis. The work is addressed at undergraduate and graduate students.

Effects of different training amplitudes on heart rate and heart rate variability in young rowers.

PubMed

Vaz, Marcelo S; Picanço, Luan M; Del Vecchio, Fabrício B

2014-10-01

The aim of this study was to investigate the autonomic nervous system recovery and the psychological response as a result of 3 training amplitudes on heart rate (HR), heart rate variability (HRV), and rate of perceived exertion (RPE) in rowing. Eight young rowers (16.8 ± 1.4 years) performed, in a randomized fashion, 2 sessions of high-intensity interval training, with high and low amplitude and a continuous training (CT) session, with the same exercise duration (10 minutes) and mean intensity (60% of maximal stroke test). The data of HR, HRV, and RPE were collected 5 minutes before, immediately after each session, and 24 hours later. High amplitude promoted higher impact in maximum HR (p ≤ 0.05) and RPE (p < 0.001) when compared with CT. For the time domain HRV variable, there was a statistically significant difference between moments of rest (pretraining or post 24 hours) and posttraining in all training sessions. Originally, we conclude that training with higher load variation between effort and recovery impacts HRV, HR, and RPE with greater intensity, but the younger rowers were ready for new training sessions 24 hours after either training method. Coaches can use the polarized training method, observing the stimulus nature and time required for recovery, because it may be an adequate strategy for the development of rower's conditioning.

Eddy-driven low-frequency variability: physics and observability through altimetry

NASA Astrophysics Data System (ADS)

Penduff, Thierry; Sérazin, Guillaume; Arbic, Brian; Mueller, Malte; Richman, James G.; Shriver, Jay F.; Morten, Andrew J.; Scott, Robert B.

2015-04-01

Model studies have revealed the propensity of the eddying ocean circulation to generate strong low-frequency variability (LFV) intrinsically, i.e. without low-frequency atmospheric variability. In the present study, gridded satellite altimeter products, idealized quasi-geostrophic (QG) turbulent simulations, and realistic high-resolution global ocean simulations are used to study the spontaneous tendency of mesoscale (relatively high frequency and high wavenumber) kinetic energy to non-linearly cascade towards larger time and space scales. The QG model reveals that large-scale variability, arising from the well-known spatial inverse cascade, is associated with low frequencies. Low-frequency, low-wavenumber energy is maintained primarily by nonlinearities in the QG model, with forcing (by large-scale shear) and friction playing secondary roles. In realistic simulations, nonlinearities also generally drive kinetic energy to low frequencies and low wavenumbers. In some, but not all, regions of the gridded altimeter product, surface kinetic energy is also found to cascade toward low frequencies. Exercises conducted with the realistic model suggest that the spatial and temporal filtering inherent in the construction of gridded satellite altimeter maps may contribute to the discrepancies seen in some regions between the direction of frequency cascade in models versus gridded altimeter maps. Finally, the range of frequencies that are highly energized and engaged these cascades appears much greater than the range of highly energized and engaged wavenumbers. Global eddying simulations, performed in the context of the CHAOCEAN project in collaboration with the CAREER project, provide estimates of the range of timescales that these oceanic nonlinearities are likely to feed without external variability.

Near-surface Heating of Young Rift Sediment Causes Mass Production and Discharge of Reactive Dissolved Organic Matter

PubMed Central

Lin, Yu-Shih; Koch, Boris P.; Feseker, Tomas; Ziervogel, Kai; Goldhammer, Tobias; Schmidt, Frauke; Witt, Matthias; Kellermann, Matthias Y.; Zabel, Matthias; Teske, Andreas; Hinrichs, Kai-Uwe

2017-01-01

Ocean margin sediments have been considered as important sources of dissolved organic carbon (DOC) to the deep ocean, yet the contribution from advective settings has just started to be acknowledged. Here we present evidence showing that near-surface heating of sediment in the Guaymas Basin, a young extensional depression, causes mass production and discharge of reactive dissolved organic matter (DOM). In the sediment heated up to ~100 °C, we found unexpectedly low DOC concentrations in the pore waters, reflecting the combined effect of thermal desorption and advective fluid flow. Heating experiments suggested DOC production to be a rapid, abiotic process with the DOC concentration increasing exponentially with temperature. The high proportions of total hydrolyzable amino acids and presence of chemical species affiliated with activated hydrocarbons, carbohydrates and peptides indicate high reactivity of the DOM. Model simulation suggests that at the local scale, near-surface heating of sediment creates short and massive DOC discharge events that elevate the bottom-water DOC concentration. Because of the heterogeneous distribution of high heat flow areas, the expulsion of reactive DOM is spotty at any given time. We conclude that hydrothermal heating of young rift sediments alter deep-ocean budgets of bioavailable DOM, creating organic-rich habitats for benthic life. PMID:28327661

DISCOVERY OF PULSATIONS, INCLUDING POSSIBLE PRESSURE MODES, IN TWO NEW EXTREMELY LOW MASS, He-CORE WHITE DWARFS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hermes, J. J.; Montgomery, M. H.; Winget, D. E.

2013-03-10

We report the discovery of the second and third pulsating extremely low mass (ELM) white dwarfs (WDs), SDSS J111215.82+111745.0 (hereafter J1112) and SDSS J151826.68+065813.2 (hereafter J1518). Both have masses < 0.25 M{sub Sun} and effective temperatures below 10, 000 K, establishing these putatively He-core WDs as a cooler class of pulsating hydrogen-atmosphere WDs (DAVs, or ZZ Ceti stars). The short-period pulsations evidenced in the light curve of J1112 may also represent the first observation of acoustic (p-mode) pulsations in any WD, which provide an exciting opportunity to probe this WD in a complimentary way compared to the long-period g-modes thatmore » are also present. J1112 is a T{sub eff} =9590 {+-} 140 K and log g =6.36 {+-} 0.06 WD. The star displays sinusoidal variability at five distinct periodicities between 1792 and 2855 s. In this star, we also see short-period variability, strongest at 134.3 s, well short of the expected g-modes for such a low-mass WD. The other new pulsating WD, J1518, is a T{sub eff} =9900 {+-} 140 K and log g =6.80 {+-} 0.05 WD. The light curve of J1518 is highly non-sinusoidal, with at least seven significant periods between 1335 and 3848 s. Consistent with the expectation that ELM WDs must be formed in binaries, these two new pulsating He-core WDs, in addition to the prototype SDSS J184037.78+642312.3, have close companions. However, the observed variability is inconsistent with tidally induced pulsations and is so far best explained by the same hydrogen partial-ionization driving mechanism at work in classic C/O-core ZZ Ceti stars.« less

Is Reaction Time Variability in ADHD Mainly at Low Frequencies?

ERIC Educational Resources Information Center

Karalunas, Sarah L.; Huang-Pollock, Cynthia L.; Nigg, Joel T.

2013-01-01

Background: Intraindividual variability in reaction times (RT variability) has garnered increasing interest as an indicator of cognitive and neurobiological dysfunction in children with attention deficit hyperactivity disorder (ADHD). Recent theory and research has emphasized specific low-frequency patterns of RT variability. However, whether…

Osteoporosis in young adults: pathophysiology, diagnosis, and management.

PubMed

Ferrari, S; Bianchi, M L; Eisman, J A; Foldes, A J; Adami, S; Wahl, D A; Stepan, J J; de Vernejoul, M-C; Kaufman, J-M

2012-12-01

Postmenopausal osteoporosis is mainly caused by increased bone remodeling resulting from estrogen deficiency. Indications for treatment are based on low areal bone mineral density (aBMD, T-score  ≤ -2.5), typical fragility fractures (spine or hip), and more recently, an elevated 10-year fracture probability (by FRAX®). In contrast, there is no clear definition of osteoporosis nor intervention thresholds in younger individuals. Low aBMD in a young adult may reflect a physiologically low peak bone mass, such as in lean but otherwise healthy persons, whereas fractures commonly occur with high-impact trauma, i.e., without bone fragility. Furthermore, low aBMD associated with vitamin D deficiency may be highly prevalent in some regions of the world. Nevertheless, true osteoporosis in the young can occur, which we define as a T-score below -2.5 at spine or hip in association with a chronic disease known to affect bone metabolism. In the absence of secondary causes, the presence of fragility fractures, such as in vertebrae, may point towards genetic or idiopathic osteoporosis. In turn, treatment of the underlying condition may improve bone mass as well. In rare cases, a bone-specific treatment may be indicated, although evidence is scarce for a true benefit on fracture risk. The International Osteoporosis Foundation (IOF) convened a working group to review pathophysiology, diagnosis, and management of osteoporosis in the young, excluding children and adolescents, and provide a screening strategy including laboratory exams for a systematic approach of this condition.

THE MASS-RICHNESS RELATION OF MaxBCG CLUSTERS FROM QUASAR LENSING MAGNIFICATION USING VARIABILITY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bauer, Anne H.; Baltay, Charles; Ellman, Nancy

2012-04-10

Accurate measurement of galaxy cluster masses is an essential component not only in studies of cluster physics but also for probes of cosmology. However, different mass measurement techniques frequently yield discrepant results. The Sloan Digital Sky Survey MaxBCG catalog's mass-richness relation has previously been constrained using weak lensing shear, Sunyaev-Zeldovich (SZ), and X-ray measurements. The mass normalization of the clusters as measured by weak lensing shear is {approx}>25% higher than that measured using SZ and X-ray methods, a difference much larger than the stated measurement errors in the analyses. We constrain the mass-richness relation of the MaxBCG galaxy cluster catalogmore » by measuring the gravitational lensing magnification of type I quasars in the background of the clusters. The magnification is determined using the quasars' variability and the correlation between quasars' variability amplitude and intrinsic luminosity. The mass-richness relation determined through magnification is in agreement with that measured using shear, confirming that the lensing strength of the clusters implies a high mass normalization and that the discrepancy with other methods is not due to a shear-related systematic measurement error. We study the dependence of the measured mass normalization on the cluster halo orientation. As expected, line-of-sight clusters yield a higher normalization; however, this minority of haloes does not significantly bias the average mass-richness relation of the catalog.« less

[Physical activity for young adults born with low body weight on the background of peers].

PubMed

Tkaczyk, Joanna; Kęska, Anna; Czajkowska, Anna; Wiśniewski, Andrzej

2010-01-01

Low birth parameters are associated with an increased risk of insulin resistance, type 2 diabetes, glucose intolerance and hypertension at later life. Regular physical activity can counteract these metabolic disorders. We determined the relation of the declared physical activity and body composition in young adults with respect to their birth weight. A total of 156 subjects (52% women and 48% men) took part in the study (the average age 20.6±1.2 years). Participants who declared regular physical activity (minimum 3 times per week) were included in group I (n=66), others in group II (n=99). In each group, the percentage of people with small (SBW) and normal (NBW) birth weight was assessed. Information about birth parameters and duration of pregnancy was obtained from medical records. Infant's mass ≤2999 g was recognized as small birth weight. Body height, body weight, waist and hips circumferences and body composition by BIA were measured. Frequency of physical activity was determined during an interview. Percentage of participants with small birth weight was respectively 17% in group I and 21% in group II. In group I standardized body height was significantly lower in subjects with SBW in comparison with those with NBW. Participants from group II with SBW had markedly lower standardized body weight and standardized BMI than adults with NBW. Independently of birth weight physically active persons characterized higher WHR values than their non active counterparts. Body fat content was significantly lower in group I (both in participants with SBW and NBW). Women and men from group I with SBW had also higher fat free mass in comparison with those from group II. Body fat content in young adults with small birth weight is related to their physical activity. People who regularly exercise had lower fat mass in comparison with non exercising ones. This is the confirmation of a protective influence of physical activity.

Time-Variable Gravity from Satellite Laser-Ranging: The Low-Degree Components and Their Connections with Geophysical/Climatic Changes

NASA Technical Reports Server (NTRS)

Chao, Benjamin F.; Cox, Christopher M.

2004-01-01

Satellite laser-ranging (SLR) has been observing the tiny variations in Earth s global gravity for over 2 decades. The oblateness of the Earth's gravity field, J2, has been observed to undergo a secular decrease of J2 due mainly to the post-glacial rebound of the mantle. Sometime around 1998 this trend reversed quite suddenly. This reversal persisted until 2001, at which point the atmosphere-corrected time series appears to have reversed yet again towards normal. This anomaly signifies a large interannual change in global mass distribution. A number of possible causes have been considered, with oceanic mass redistribution as the leading candidate although other effects, such as glacial melting and core effects may be contributing. In fact, a strong correlation has been found between the J2 variability and the Pacific decadal oscillation. It is relatively more difficult to solve for corresponding signals in the shorter wavelength harmonics from the existing SLR-derived time variable gravity results, although it appears that geophysical fluid mass transport is being observed. For example, the recovered J3 time series shows remarkable agreement with NCEP-derived estimates of atmospheric gravity variations. Likewise, some of the non-zonal harmonic components have significant interannual signal that appears to be related to mass transport related to climatic effects such as El Nino Southern Oscillation. We will present recent updates on the J2 evolution, as well as a monthly time sequence of low-degree component map of the time-variable gravity complete through degree 4, and examine possible geophysical/climatic causes.

The Stellar Mass-Halo Mass Relation for Low-mass X-Ray Groups At 0.5< z< 1 in the CDFS With CSI

NASA Astrophysics Data System (ADS)

Patel, Shannon G.; Kelson, Daniel D.; Williams, Rik J.; Mulchaey, John S.; Dressler, Alan; McCarthy, Patrick J.; Shectman, Stephen A.

2015-02-01

Since z˜ 1, the stellar mass density locked in low-mass groups and clusters has grown by a factor of ˜8. Here, we make the first statistical measurements of the stellar mass content of low-mass X-ray groups at 0.5\\lt z\\lt 1, enabling the calibration of stellar-to-halo mass scales for wide-field optical and infrared surveys. Groups are selected from combined Chandra and XMM-Newton X-ray observations in the Chandra Deep Field South. These ultra-deep observations allow us to identify bona fide low-mass groups at high redshift and enable measurements of their total halo masses. We compute aggregate stellar masses for these halos using galaxies from the Carnegie-Spitzer-IMACS (CSI) spectroscopic redshift survey. Stars comprise ˜3%-4% of the total mass of group halos with masses {{10}12.8}\\lt {{M}200}/{{M}⊙ }\\lt {{10}13.5} (about the mass of Fornax and one-fiftieth the mass of Virgo). Complementing our sample with higher mass halos at these redshifts, we find that the stellar-to-halo mass ratio decreases toward higher halo masses, consistent with other work in the local and high redshift universe. The observed scatter about the stellar-halo mass relation is σ ˜ 0.25 dex, which is relatively small and suggests that total group stellar mass can serve as a rough proxy for halo mass. We find no evidence for any significant evolution in the stellar-halo mass relation since z≲ 1. Quantifying the stellar content in groups since this epoch is critical given that hierarchical assembly leads to such halos growing in number density and hosting increasing shares of quiescent galaxies. This Letter includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. This research is based on observations made with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555.

Longitudinal Study of Body Mass Index in Young Males and the Transition to Fatherhood

PubMed Central

Garfield, Craig F.; Duncan, Greg; Gutina, Anna; Rutsohn, Joshua; McDade, Thomas W.; Adam, Emma K.; Coley, Rebekah Levine; Chase-Lansdale, P. Lindsay

2017-01-01

Despite a growing understanding that the social determinants of health have an impact on body mass index (BMI), the role of fatherhood on young men’s BMI is understudied. This longitudinal study examines BMI in young men over time as they transition from adolescence into fatherhood in a nationally representative sample. Data from all four waves of the National Longitudinal Study of Adolescent Health supported a 20-year longitudinal analysis of 10,253 men beginning in 1994. A “fatherhood-year” data set was created and changes in BMI were examined based on fatherhood status (nonfather, nonresident father, resident father), fatherhood years, and covariates. Though age is positively associated with BMI over all years for all men, comparing nonresident and resident fathers with nonfathers reveals different trajectories based on fatherhood status. Entrance into fatherhood is associated with an increase in BMI trajectory for both nonresident and resident fathers, while nonfathers exhibit a decrease over the same period. In this longitudinal, population-based study, fatherhood and residence status play a role in men’s BMI. Designing obesity prevention interventions for young men that begin in adolescence and carry through young adulthood should target the distinctive needs of these populations, potentially improving their health outcomes. PMID:26198724