1,800 research outputs found

    Does the California market squid (Loligo opalescens) spawn naturally during the day or at night? A note on the successful use of ROVs to obtain basic fisheries biology data

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    The California market squid (Loligo opalescens Berry), also known as the opalescent inshore squid (FAO), plays a central role in the nearshore ecological communities of the west coast of the United States (Morejohn et al., 1978; Hixon, 1983) and it is also a prime focus of California fisheries, ranking first in dollar value and tons landed in recent years (Vojkovich, 1998). The life span of this species is only 7−10 months after hatching, as ascertained by aging statoliths (Butler et al., 1999; Jackson, 1994; Jackson and Domier, 2003) and mariculture trials (Yang, et al., 1986). Thus, annual recruitment is required to sustain the population. The spawning season ranges from April to November and spawning peaks from May to June. In some years there can be a smaller second peak in November. In Monterey Bay, the squids are fished directly on the egg beds, and the consequences of this practice for conservation and fisheries management are unknown but of some concern (Hanlon, 1998). Beginning in April 2000, we began a study of the in situ spawning behavior of L. opalescens in the southern Monterey Bay fishing area

    The High A(V) Quasar Survey: Reddened quasi-stellar objects selected from optical/near-infrared photometry - II

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    Quasi-stellar objects (QSOs) whose spectral energy distributions (SEDs) are reddened by dust either in their host galaxies or in intervening absorber galaxies are to a large degree missed by optical color selection criteria like the one used by the Sloan Digital Sky Survey (SDSS). To overcome this bias against red QSOs, we employ a combined optical and near-infrared color selection. In this paper, we present a spectroscopic follow-up campaign of a sample of red candidate QSOs which were selected from the SDSS and the UKIRT Infrared Deep Sky Survey (UKIDSS). The spectroscopic data and SDSS/UKIDSS photometry are supplemented by mid-infrared photometry from the Wide-field Infrared Survey Explorer. In our sample of 159 candidates, 154 (97%) are confirmed to be QSOs. We use a statistical algorithm to identify sightlines with plausible intervening absorption systems and identify nine such cases assuming dust in the absorber similar to Large Magellanic Cloud sightlines. We find absorption systems toward 30 QSOs, 2 of which are consistent with the best-fit absorber redshift from the statistical modeling. Furthermore, we observe a broad range in SED properties of the QSOs as probed by the rest-frame 2 {\mu}m flux. We find QSOs with a strong excess as well as QSOs with a large deficit at rest-frame 2 {\mu}m relative to a QSO template. Potential solutions to these discrepancies are discussed. Overall, our study demonstrates the high efficiency of the optical/near-infrared selection of red QSOs.Comment: 64 pages, 18 figures, 16 pages of tables. Accepted to ApJ

    Entry, Descent, and Landing Operations Analysis for the Stardust Re-Entry Capsule

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    On the morning of January 15, 2006, the Stardust capsule successfully landed at the Utah Test and Training range in northwest Utah returning cometary samples from the comet Wild-2. An overview of the entry, descent, and landing (EDL) trajectory analysis that was performed for targeting during the Stardust Mission Navigation Operations Phase upon final approach to Earth is described. In addition, how the predicted landing location and the resulting overall 99 percentile landing footprint ellipse obtained from a Monte Carlo analysis changed over the final days and hours prior to entry is also presented. The navigation and EDL operations effort accurately delivered the entry capsule to the desired landing site. The final landing location was 8.1 km from the target, which was well within the allowable landing area

    Kepler423b: a half-Jupiter mass planet transiting a very old solar-like star

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    We report the spectroscopic confirmation of the Kepler object of interest KOI-183.01 (Kepler-423b), a half-Jupiter mass planet transiting an old solar-like star every 2.7 days. Our analysis is the first to combine the full Kepler photometry (quarters 1-17) with high-precision radial velocity measurements taken with the FIES spectrograph at the Nordic Optical Telescope. We simultaneously modelled the photometric and spectroscopic data-sets using Bayesian approach coupled with Markov chain Monte Carlo sampling. We found that the Kepler pre-search data conditioned (PDC) light curve of KOI-183 exhibits quarter-to-quarter systematic variations of the transit depth, with a peak-to-peak amplitude of about 4.3 % and seasonal trends reoccurring every four quarters. We attributed these systematics to an incorrect assessment of the quarterly variation of the crowding metric. The host star KOI-183 is a G4 dwarf with M⋆=0.85±0.04M_\star=0.85\pm0.04 M_\rm{Sun}, R⋆=0.95±0.04R_\star=0.95\pm0.04 R_\rm{Sun}, Teff=5560±80T_\mathrm{eff}=5560\pm80 K, [M/H]=−0.10±0.05[M/H]=-0.10\pm0.05 dex, and with an age of 11±211\pm2 Gyr. The planet KOI-183b has a mass of Mp=0.595±0.081M_\mathrm{p}=0.595\pm0.081 MJup_\mathrm{Jup} and a radius of Rp=1.192±0.052R_\mathrm{p}=1.192\pm0.052 RJup_\mathrm{Jup}, yielding a planetary bulk density of ρp=0.459±0.083\rho_\mathrm{p}=0.459\pm0.083 g/cm3^{3}. The radius of KOI-183b is consistent with both theoretical models for irradiated coreless giant planets and expectations based on empirical laws. The inclination of the stellar spin axis suggests that the system is aligned along the line of sight. We detected a tentative secondary eclipse of the planet at a 2-σ\sigma confidence level (ΔFec=14.2±6.6\Delta F_{\mathrm{ec}}=14.2\pm6.6 ppm) and found that the orbit might have a small non-zero eccentricity of e=0.019−0.014+0.028e=0.019^{+0.028}_{-0.014}. With a Bond albedo of AB=0.037±0.019A_\mathrm{B}=0.037\pm0.019, KOI-183b is one of the gas-giant planets with the lowest albedo known so far.Comment: 13 pages, 13 figures, 5 tables. Accepted for publication in A&A. Planet designation changed from KOI-183b to Kepler-423

    Complementary feeding practices and associated factors of dietary diversity among uncomplicated severe acute malnourished children aged 6-23 months in Burkina Faso

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    Nutritional treatment of children with uncomplicated severe acute malnutrition (SAM) is based on ready-to-use therapeutic foods (RUTF). With treatment provided at community level, children could have access to other foods, and a reduction in the dose of RUTF could further increase dietary diversity during treatment. We assessed the dietary diversity score (DDS), the minimum dietary diversity (MDD), the minimum meal frequency (MMF) and the minimum acceptable diet (MAD) of 459 infants and young children aged 6-23 months being treated for SAM with different doses of RUTF. We also investigated the factors associated with DDS. Dietary intake was estimated using a single 24-h multipass dietary recall, 1 month after starting treatment, from December 2016 to August 2018. The DDS was calculated on the basis of eight food groups. Differences between children receiving the reduced RUTF and the standard RUTF dose and factors associated with DDS were assessed by Poisson and logistic regression models. RUTF dose was not associated with DDS (4.07 +/- 1.25 for reduced RUTF and 4.01 +/- 1.26 for standard RUTF; P = 0.77). Food groups most consumed by children were grains, roots or tubers (96%) and legumes and nuts (72%). Eggs consumption was low (3%). DDS was positively associated with child's age, mother's education, household wealth index, urban residence and rainy season. The present findings show that children with SAM consumed a variety of foods during treatment in addition to the RUTF ration prescribed to them. Reducing the dose of RUTF during SAM treatment did not impact DDS

    The host galaxy and late-time evolution of the Super-Luminous Supernova PTF12dam

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    Super-luminous supernovae of type Ic have a tendency to occur in faint host galaxies which are likely to have low mass and low metallicity. PTF12dam is one of the closest and best studied super-luminous explosions that has a broad and slowly fading lightcurve similar to SN 2007bi. Here we present new photometry and spectroscopy for PTF12dam from 200-500 days (rest-frame) after peak and a detailed analysis of the host galaxy (SDSS J142446.21+461348.6 at z = 0.107). Using deep templates and image subtraction we show that the full lightcurve can be fit with a magnetar model if escape of high-energy gamma rays is taken into account. The full bolometric lightcurve from -53 to +399 days (with respect to peak) cannot be fit satisfactorily with the pair-instability models. An alternative model of interaction with a dense CSM produces a good fit to the data although this requires a very large mass (~ 13 M_sun) of hydrogen free CSM. The host galaxy is a compact dwarf (physical size ~ 1.9 kpc) and with M_g = -19.33 +/- 0.10, it is the brightest nearby SLSN Ic host discovered so far. The host is a low mass system (2.8 x 10^8 M_sun) with a star-formation rate (5.0 M_sun/year), which implies a very high specific star-formation rate (17.9 Gyr^-1). The remarkably strong nebular lines provide detections of the [O III] \lambda 4363 and [O II] \lambda\lambda 7320,7330 auroral lines and an accurate oxygen abundance of 12 + log(O/H) = 8.05 +/- 0.09. We show here that they are at the extreme end of the metallicity distribution of dwarf galaxies and propose that low metallicity is a requirement to produce these rare and peculiar supernovae.Comment: 20 pages, 12 figures, 8 tables, accepted for publication to MNRA

    Near-infrared evolution of the equatorial ring of SN 1987A

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    We use adaptive-optics imaging and integral field spectroscopy from the Very Large Telescope, together with images from the \emph{Hubble Space Telescope}, to study the near-infrared (NIR) evolution of the equatorial ring (ER) of SN~1987A. We study the NIR line and continuum flux and morphology over time in order to lay the groundwork for \emph{James Webb Space Telescope} observations of the system. We also study the differences in the interacting ring structure and flux between optical, NIR and other wavelengths, and between line and continuum emission, to constrain the underlying physical processes. Mostly the evolution is similar in the NIR and optical. The morphology of the ER has been skewed toward the west side (with roughly 2/3 of the NIR emission originating there) since around 2010. A steady decline in the ER flux, broadly similar to the MIR and the optical, is ongoing since roughly this time as well. The expansion velocity of the ER hotspots in the NIR is fully consistent with the optical. However, continuum emission forms roughly 70 per cent of the NIR luminosity, and is relatively stronger outside the hotspot-defined extent of the ER than the optical emission or NIR line emission since 2012--2013, suggesting a faster-expanding continuum component. We find that this outer NIR emission can have a significant synchrotron contribution. Even if emission from hot (∌\sim2000~K) dust is dominant within the ER, the mass of this dust must be vanishingly small (a few ×10−12\times10^{-12}~M⊙_\odot) compared to the total dust mass in the ER (≳10−5\gtrsim10^{-5}~M⊙_\odot) to account for the observed HKsHKs flux. The NIR continuum emission, however, expands slower than the more diffuse 180-K dust emission that dominates in the MIR, indicating a different source, and the same hot dust component cannot account for the JJ-band emission.Comment: 17 pages, 17 figures. Accepted for publication in Astronomy & Astrophysic

    Morphology of the spectral resonance structure of the electromagnetic background noise in the range of 0.1?4 Hz at <i>L</I> = 5.2

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    International audienceContinuous observations of fluctuations of the geomagnetic field at SodankylÀ Geophysical Observatory (L = 5.2) were used for a comprehensive morphological study of the spectral resonance structure (SRS) seen in the background electromagnetic noise in the frequency range of 0.1?4.0 Hz. It is shown that the occurrence rate of SRS is higher in the nighttime than in the daytime. The occurrence rate is higher in winter than in summer. The SRS frequencies and the difference between neighbouring eigenfrequencies (the frequency scale) increase towards nighttime and decrease towards daytime. Both frequency scale and occurrence rate exhibit a clear tendency to decrease from minimum to maximum of the solar activity cycle. It is found that the occurrence rate of SRS decreases when geomagnetic activity increases. The SRS is believed to be a consequence of a resonator for Alfvén waves, which is suggested to exist in the upper ionosphere. According to the theory of the ionospheric Alfvén resonator (IAR), characteristics of SRS crucially depend on electron density in the F-layer maximum, as well as on the altitudinal scale of the density decay above the maximum.We compared the SRS morphological properties with predictions of the IAR theory. The ionospheric parameters needed for calculation were obtained from the ionosphere model (IRI-95), as well as from measurements made with the ionosonde in SodankylÀ. We conclude that, indeed, the main morphological properties of SRS are explained on the basis of the IAR theory. The measured parameters of SRS can be used for improving the ionospheric models
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