Low-Metallicity

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Revealing the cold dust in low-metallicity
          environments

Revealing the cold dust in low-metallicity environments

example, see Dale et al. 2012 , for KINGFISH). Indeed we allow our β obs to go to very low values, giving lower dust masses than if we fixed it to 1.5 or even 2.0: as we allow a greater emission effciency for the grains, we need less mass than if we were using a higher emissivity index, to account for the same amount of luminosity. We perform the test by fixing the emissivity index parameter to 1.5 then 2.0 but find that the dust masses were increasing by only a factor ∼1.5−3, again insu fficient to explain the order of magnitude di fference between the proportion of dust relative to the stars between the metal-poor and metal-rich galaxies. Nonetheless, with our modified blackbody fits we are considering only one temperature and grain size. We may be missing here a fraction of the dust mass coming from warmer big grains, and this contribution may be more important in low-metallicity galaxies rather than in more metal-rich ones. Thus, part of the observed trend may just be a side e ffect of using modified blackbodies. The mass corresponding to the stochastically heated grains is, however, negligible. In a follow-up paper (Rémy-Ruyer et al., in prep.), we will obtain
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Massive Oe/Be stars at low metallicity: Candidate progenitors of long GRBs?

Massive Oe/Be stars at low metallicity: Candidate progenitors of long GRBs?

The angular momentum still available at this late phase of stellar evolution is the larger, the less mass and, therefore, angular momentum the progenitor star has lost during its lifetime. Since radiatively driven mass loss from massive stars decreases with metallicity, this has led to the notion that low-metallicity star-forming regions should be preferred hosts of GRBs. In fact, observations are beginning to support this picture (e.g., Modjaz et al. 2008). Moreover, the GRB rate per unit mass increases with redshift z. But it is not clear whether this requires any explanation other than the general increase in star formation with redshift (up to z∼2).
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Transiting exoplanets from the CoRoT space mission IX. CoRoT-6b: a transiting `hot Jupiter' planet in an 8.9d orbit around a low-metallicity star

Transiting exoplanets from the CoRoT space mission IX. CoRoT-6b: a transiting `hot Jupiter' planet in an 8.9d orbit around a low-metallicity star

The period derived from the the CoRoT light curve is fully in phase with that derived from the radial velocity measure- ments. The bootstrap analysis described in Sect. 2.2 is consis- tent with the eccentricity of the planetary orbit being ≤ 0.1, as derived from an analysis of the radial velocity curve (Sect. 3.2). While circularisation of planetary orbits may take quite some time (Jackson et al. 2008), we note that the age of the CoRoT- 6b system derived below is consistent with a low value to the ec- centricity at the distance of 0.08 AU. We used the evolutionary models of Guillot (2008) to investigate whether a planet with a relatively longer period (and thus less incident radiation) would behave di fferently from a more ‘classical’ hot Jupiter. As can be seen from the results in Fig. 12, it does not. It is also a modestly inflated planet requiring: (1) a low core mass, consistent with the low-metallicity of the parent star and the star-planet metal- licity correlation; and (2) either some tidal dissipation (equiv- alent to a few % of the incoming stellar heat flux) or an order of magnitude higher interior opacity than is generally assumed. To estimate the expected thermal evaporation of CoRoT-6b, we applied the method described in Lammer et al. (2009) and ob- tained mass loss rates given by dM dt ∼ 2 × 10 −8 g s −1 that are
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Evolution of massive Be and Oe stars at low metallicity towards the Long Gamma Ray bursts\footnote{Based on ESO runs 069.D-0275(A), 072.D-0245(A) and (C).}

Evolution of massive Be and Oe stars at low metallicity towards the Long Gamma Ray bursts\footnote{Based on ESO runs 069.D-0275(A), 072.D-0245(A) and (C).}

6 Observatorio Astronomico de Valencia, 46980 Paterna Valencia, Spain 7 Geneva Observatory, University of Geneva, Maillettes 51, 1290 Sauverny, Switzerland Abstract: Several studies have shown recently that at low metallicity B-type stars rotate faster than in envi- ronments of high metallicity. This is a typical case in the SMC. As a consequence, it is expected that a larger number of fast rotators is found in the SMC than in the Galaxy, in particular a higher fraction of Be/Oe stars. Using the ESO-WFI in its slitless mode, the data from the SMC open clusters were examined and an occurrence of Be stars 3 to 5 times larger than in the Galaxy was found. The evolution of the angular rotational velocity at different metallicities seems to be the main key to understand the specific behavior and evolution of these stars. According to the results from this WFI study, the observational clues obtained from the SMC WR stars and massive stars, and the theoretical predictions of the characteristics must have the long gamma-ray burst progenitors, we have identified the low metallicity massive Be and Oe stars as potential LGRB progenitors. To this end, the ZAMS rotational velocities of the SMC Be/Oe stars were determined and compared to models. The expected rates and the numbers of LGRB were then calculated and compared to the observed ones. Thus, a high probability was found that low metallicity Be/Oe stars can be LGRB progenitors. In this document, we describe the different steps followed in these studies: determination of the number of Be/Oe stars at dif- ferent metallicities, identification of the clues that lead to suppose the low metallicity Be/Oe stars as LGRB progenitors, comparison of models with observations.
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Modeling the physical properties in the ISM   of the low-metallicity galaxy NGC 4214

Modeling the physical properties in the ISM of the low-metallicity galaxy NGC 4214

Tielens & Hollenbach 1985 ). By studying the latter, we can in- vestigate the conditions of the molecular clouds, which in turn will be potential sites for the next episode of star formation. How does the propagation of radiation and the ISM com- position a ffect ISM observables in low-metallicity galaxies? Addressing this question is important to understand the evo- lution of low-metallicity galaxies, which undergo more bursty star formation than normal galaxies. Nearby star-forming dwarf galaxies present distinct observational signatures compared to well-studied disk galaxies. Dwarfs are usually metal poor, H i rich, and molecule poor as a result of large-scale photodisso- ciation (e.g., Kunth & Östlin 2000 ; Hunter et al. 2012 ; Schruba et al. 2012 ). Mid-IR (MIR) and far-IR (FIR) observations have
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Massive Be and Oe stars at low metallicity and long gamma ray bursts

Massive Be and Oe stars at low metallicity and long gamma ray bursts

2.2. rotational velocities at low metallicity As shown in Sect. 2.1, the occurrence of the Be phenomenon is larger in lower metallicity envi- ronment. It is explained by the fact that at lower metallicity O, B, A, and Be stars rotate faster than their counterparts in higher metallicity en- vironment (Keller 2004; Martayan et al. 2006, 2007; Hunter et al. 2008). It is due to their lower mass-loss at low metallicity (Bouret et al. 2003; Vink 2007) that implies a lower angu- lar momentum loss (Maeder & Meynet 2001).

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On the behaviour of B and Be stars at low metallicity.

On the behaviour of B and Be stars at low metallicity.

Abstract. We present new results obtained with the VLT GIRAFFE for a large sample of B and Be stars belonging to the Magellanic Clouds, i.e. at low metallicity. First, we show the effects of the metallicity of the environment on their rotation (linear, angular, and at the ZAMS). Second, we present the analysis of the effects of metallicity and evolution on the appearance of Be stars. We also new present results about the proportions of Be stars to B stars. Third, by cross-correlation with large photometric surveys such as MACHO and OGLE, we report on the detection for the first time of short-term multi-periodicity in 9 Be stars in the Small Magellanic Cloud, which can be interpreted in terms of pulsations.
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The extra-mixing efficiency in very low metallicity RGB stars

The extra-mixing efficiency in very low metallicity RGB stars

2 A. Recio-Blanco and P. de Laverny: The extra-mixing efficiency in very low metallicity RGB stars nature and efficiency are still objects of debate (see, for in- stance, Palacios et al. 2006). Furthermore, the extra-mixing ef- ficiency at very low metal content is still poorly known, as is its metallicity dependence. We therefore present here carbon iso- topic ratios of RGB stars in GC ten times metal-poorer (down to [Fe/H] ∼ -2.5) than presented in Shetrone (2003). They were derived from low-resolution spectra around the second over- tone bands of the CO molecule at 2.3µm. The selection of the targets, the observations, and their reduction are presented in Sect. 2. Sect. 3 is devoted to the derivation of the 12 C/ 13 C ratios
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Probing the impact of metallicity on the dust properties in galaxies

Probing the impact of metallicity on the dust properties in galaxies

Having reliable probes and diagnostics of the properties of the ISM phases in low-metallicity galaxies is necessary to start tackling these issues. A complete and well-sampled wavelength cover- age of the SED is also needed to disentangle the effects of various parameters, such as metallicity, star-formation activity, morphology etc., on the ISM properties and on the processes regulating them. The advent of the Herschel Space Observatory at the very beginning of my PhD, provided new constraints on the FIR-to-submm domain of the SED. Before Herschel, the wavelength ranges accessible to the scientific community with IRAS, ISO, Spitzer, AKARI and ground-based facilities (suffering from contamination by Earth’s atmosphere) were indeed poorly sampling the bulk of the dust emission beyond ∼ 160 µm in the FIR-submm and direct observations of the most important gas cooling lines in the FIR were missing. Moreover, the sensitivities reached by these instruments enabled accurate studies only for the brightest and highest metallicity dwarf galaxies. With its unprecedented sensitivity and wavelength coverage, Herschel now provides a unique opportunity to study dust and gas in the lowest-metallicity galaxies, enabling more systematic studies of these environments over a larger range of metallicities.
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The luminosity-metallicity relation in the local Universe from the 2dF Galaxy Redshift Survey

The luminosity-metallicity relation in the local Universe from the 2dF Galaxy Redshift Survey

The R 23 parameter has been calibrated and correlated with metal- licity by measuring oxygen abundances using the direct method, i.e. based on estimates of electronic density and temperature, for a large sample of H II regions in the low-metallicity regime and using pho- toionization models for the high-metallicity regime (see Garnett 2002 for a review). The direct method suffers from severe limita- tions, such as the restricted range of the ionization parameters and/or metallicities and the observability of intrinsic weak lines. This makes this method difficult to use for abundance estimates, espe- cially for galaxies at cosmological distances. There are several rea- sons for questioning the accuracy of both abundance scales (see Ken- nicutt et al. (2003) for a detailed discussion of different issues related to this topic). Pilyugin (2000) has provided new calibrations to im- plement McGaugh (1991) corrections into the empirical strong-line method. This method, usually called the ‘P-method’, is claimed to be more accurate for low-ionization H II regions and for metal-poor
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Determining the metallicity of the solar envelope using seismic inversion techniques

Determining the metallicity of the solar envelope using seismic inversion techniques

symbols are associated with values of θ between 10 −5 and 10 −8 . The first result is that a very large majority of inversions favour a low metallicity, as presented in Vorontsov et al. ( 2014 ). Only one small region of the parameter space, for the inversion of Model 4, built with the CEFF equation of state, gives a high metallicity as a solution. However, this solution is not very trustworthy since it is associated with a high cross-term kernel of A. This high cross-term value is a consequence of the parameter set used, which is that of the less stable inversions presented in Sect. 3 . Inversions of the convective parameter have shown that Model 4 pre- sented large discrepancies with the Sun in its A profile, thus showing the need to damp the the cross-term contribution for this model. When such a damping is realised, the so- lution directly changes to a low-metallicity one. This leads us to consider that these particular results, obtained with a particular parameter set are not to be trusted. Moreover, even for the other models, this set gave higher metallicities, indicating that a systematic error, stemming from the A dif- ferences with the Sun, was potentially re-introduced. Based on these considerations, we consider that the inverted re- sults obtained with this parameter set are not to be trusted. Ultimately, one finds out that the given interval is between [0.008, 0.0014]. While the lowest values of this inversion seem unrealistically low, one should keep in mind that errors of the order of 3.0 × 10 −3 have been observed in the hare-and- hounds exercises, explaining the interval obtained here. This spread is a consequence of the variations in the ingredients of the microphysics in the models, which lead to better or worse agreement with the acoustic structure of the Sun.
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Metallicity vs. Be phenomenon relation in the solar neighborhood

Metallicity vs. Be phenomenon relation in the solar neighborhood

In order to separate the stars in two sets carrying possible information on differences in initial matallicity content, we separated them into “galactic- center” and “galactic anti-center” groups. Fig. 1b shows that there is no no- ticeable difference in the “age vs. mass” distributions thus obtained. The most striking differences are: a) the number of Be stars in the ”galactic-center” group outnumbers the “anti-center” one; b) there are younger Be stars in the anti- center direction. Finding a) may agree with the fact that low metallicity favors fast rotation (Maeder et al. 1999). However, the distinction between both groups could be more reliable if we could see differences in the number fractions N(Be)/N(B+Be).
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The correlation between mixing length and metallicity on the giant branch: implications for ages in the Gaia era

The correlation between mixing length and metallicity on the giant branch: implications for ages in the Gaia era

5. WHY WASN’T THIS NOTICED BEFORE? Given the strength of this effect, it seems surprising that it was not previously recognized. In fact, offsets from isochrones have been noticed both in metal-poor globular clusters (e.g. Brasseur et al. 2010; Cohen et al. 2015) and metal-rich bulge stars (Ness et al. 2013). Ad- ditionally, work on open clusters has indicated that de- pending on the choice of models, isochrones can be too blue in some bands and too red in others (see e.g. Hayes et al. 2015). However, since each of these regimes is usually analyzed individually, using each author’s choice of models and colors, this likely made it more diffi- cult to identify a systematic offset between the models and the data. We suspect that the calibration of the color-temperature relations and the reddening assump- tions could also be masking the offset. In low metallicity clusters, for example, where the model giant branch was bluer than the data, it is likely that increased reddening or higher metallicity were assumed during the isochrone fitting in order to make the models better match the data. When combined with the fact that most authors studying star clusters do qualitative, rather than quanti- tative, assessments of the accuracy of their giant branch locations after fitting to the location of the main sequence or main sequence turnoff, it is somewhat less surprising that these offsets of only about 100 K were not noticed previously.
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Metallicity dependence of high-mass X-ray binary populations

Metallicity dependence of high-mass X-ray binary populations

change in the population size, plus a minor one originated in the variation of the mean HMXB luminosity. Finally, it is important to point out that although the simplest model that describes the dependence of the number of HMXBs on the oxygen abundance is a split function, there is no physi- cal evidence to justify the break at 12 + log(O/H) ' 8. Hence, following the apparent linear trend shown by the number of ob- served HMXBs in Fig. 4 , as a second approach we also param- eterized the factor Q by a linear function of the oxygen abun- dance. A fit to our whole sample confirms the existence of a dependence of Q on metallicity with a confidence greater than 1−5 × 10 −5 . However, the best-fit parameters suggest that the an- ticorrelation between the number of binaries and the metallicity of the galaxies is milder than that predicted by a sharp break. In this case the change in the population size per unit SFR is only −0.14 dex per dex. The discrepancy is originated in the bet- ter statistics of high-metallicity data, which have more weight in the fit than low-metallicity ones, hence biasing the slope to shal- lower values. A deeper exploration of this issue would require larger samples, and a more detailed treatment of population size fluctuations.
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The Low-Threshold Calcium Channel Cav3.2 Determines Low-Threshold Mechanoreceptor Function

The Low-Threshold Calcium Channel Cav3.2 Determines Low-Threshold Mechanoreceptor Function

Fast-conducting myelinated axons and large cell bodies char- acterize A-fiber-associated sensory neurons (Aa, b, or d), which are involved mostly in touch and proprioception. Slowly con- ducting unmyelinated fibers with small cell bodies correspond to C-fibers involved in not only nociception but also conveying tactile information. LTMRs are heterogeneous; comprise Ab-, Ad-, and C-fiber subtypes; and are further subdivided according to their rate of adaptation to mechanical stimuli and by their distal and central terminal anatomy ( Li et al., 2011 ). However, molecu- lar markers of LTMRs remain insufficient to fully decipher their pathophysiological roles. Recently, a small population of unmy- elinated dorsal root ganglia (DRG) neurons has been described for their unique expression of tyrosine hydroxylase (TH), vesicu- lar transporter of glutamate 3 (VGLUT3), and chemokine like pro- tein TAFA4 ( Brumovsky et al., 2006; Delfini et al., 2013; Seal et al., 2009 ). These neurons represent the poorly understood population of C-LTMRs involved in apparently opposing sensa- tions of pleasant touch and hypersensitivity during chronic pain ( Bessou et al., 1971; Seal et al., 2009 ). Another specific popula- tion of LTMRs is the TrkB-expressing neurons innervating D-hair follicles and described as Ad-LTMRs. Interestingly, these neu- rons express the Cav3.2 isoform of low-voltage-activated cal- cium channels ( Shin et al., 2003 ).
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Low Coherence Interferometry

Low Coherence Interferometry

Low Coherence Interferometry 4.1. Introduction Optical wave frequencies are very high, the eye and other detectors respond to light intensity only, in other words to the time average of the electric field amplitude squared. For this reason, we almost totally miss the sinusoidal wave character of light in our daily life. In order to get full access to the phase of a lightwave experimentally, it is necessary to use interferometric techniques. Two centuries after Young and Fresnel’s experiments, interferometry remains a very active domain of research: more precisely, the definition of new measurement systems. The reason for this vivid activity is the fact that the phase of a light wave is a real goldmine of information about the media through which this wave has been propagating since it is proportional firstly to the propagation distance inside the media, and secondly to their refractive index. Therefore, any change in the propagation distance of a wavelength fraction can be detected in the phase, and we can for this reason proceed to very precise measurements of small displacements. As far as the refractive index is concerned and bound to the structure of a material, any external strain (heat, pressure, electric field, etc.) modifying this structure also modifies the refractive index, and therefore the phase. If we then have a relevant theory connecting the phase with the constraint and successful inverse methods, it is possible to find the constraint applied by the phase measurement. Finally, the studied system is generally weakly perturbed by the measurement due to the nature of the interaction between light and matter.
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Exploring low carbon futures.

Exploring low carbon futures.

  Mediation  between  actors  and  domains.   The  GETS  device  provided  a  strong  basis  for  coordination  among  the  main  stakeholders   of   the   inquiry   on   carbon   markets:   the   electricity   sector,   the   industry,   the   European   Commission,   economists,   iNGOs,   etc.   First,   its   collective   design   enabled   the   sharing   of   heterogeneous   knowledge:   economic   theory;   knowledge   on   technology   development   capacities;  modelling;  financial  markets,  etc.  This  knowledge  was  shared  through  the  collective   engineering  of  the  GETS  device  and  embedded  in  various  details  (tools,  models,  instruments,   etc.).   The   role   play   provided   the   actors   of   the   GETS   experiment   with   shared   knowledge   and   expectations  regarding  the  carbon  market.  Second,  the  exploratory  status  of  the  GETS  enabled   cooperative   relations   that   might   have   been   difficult   to   obtain   directly   in   the   arena   of   stakeholder   consultation.   In   particular,   the   interactions   between   the   Commission   and   the   organisers  of  the  GETS  help  explain  the  similarities  between  the  two  designs.  Thus,  the  GETS   mediated  between  people  and  domains  of  knowledge  that  don’t  coexist  easily.  By  enabling  the   management   of   knowledge   about   both   carbon   markets   and   a   low   carbon   future,   the   GETS   supported  the  constitution  of  an  epistemic  community  (Amin  and  Cohendet,  2004).  
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Low Delay Transform for High Quality Low Delay Audio Coding

Low Delay Transform for High Quality Low Delay Audio Coding

In order to evaluate the proposed method for low delay block switching in real life low delay audio coding, several experiments based on Low Delay AAC (LD-AAC) and Enhanced Low Delay AAC (ELD-AAC) were con- ducted and are presented in the first part of this Chapter. The LD-AAC [Al- lamanche 99] is the initial low delay version of the AAC [ISO 09]. This ex- tension of AAC has been standardized in 2000 with the goal to reduce the source of delay. For this purpose, the block switching has been removed and the frame length has been reduced to 512 or 480 samples. For a 48 kHz input signal, the minimum total algorithmic delay of the LD-AAC is then 20 ms if the bit reservoir is not used. The bit reservoir allows to hold part of the next frame's audio data in order to temporary change the effective bit rate. It is usually not used in low delay applications as it implicitly intro- duces an additional delay. The Enhanced Low Delay AAC (ELD-AAC) is the last evolution of the low delay version of the MPEG-4 Audio toolbox [ISO 09]. The ELD-AAC is based on the LD-AAC codec with the addition of the SBR module allowing to achieve a better quality for low bit rate and with the replacement of the MDCT by the Low Delay Transform as de- scribed in section 3.1.3 [Schnell 08]. The minimum total algorithmic delay of the ELD-AAC is 15 ms and is obtained when the SBR tool is not used at 48 kHz sampling frequency. With SBR, the algorithmic delay is increased to 31.3 ms, the SBR tool operating at this initial sampling frequency and the AAC core at half the sampling frequency.
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Traffic analysis of low and ultra-low frame-rate videos

Traffic analysis of low and ultra-low frame-rate videos

3.3.1 Dataset Overview The MIO-TCD dataset contains a total of 786,702 images, 137,743 being high- resolution video frames showing multiple vehicles and 648,959 lower-resolution images of cropped vehicles. These images were acquired at different times of the day and different periods of the year by nearly a thousand traffic cameras deployed across Canada and the United States. Those images have been selected to cover a wide range of challenges and are typical of visual data captured in urban and rural traffic scenarios. The dataset includes images: (1) taken at different times of the day, (2) with various levels of traffic density and vehicle occlusion, (3) showing small moving objects due to low resolution and/or perspective, (4) showing vehicles with different orientations, (5) taken under challenging weather conditions, and (6) exhibiting strong compression artifacts. This dataset has been carefully annotated by a team of nearly 200 people to enable a quantitative comparison and ranking of various algorithms.
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ELODIE metallicity-biased search for transiting Hot Jupiters II. A very hot Jupiter transiting the bright K star HD189733

ELODIE metallicity-biased search for transiting Hot Jupiters II. A very hot Jupiter transiting the bright K star HD189733

tween the V − K colour and radii measured from interferome- try that shows very little dispersion for low-mass stars (∼ 1 %). This calibration gives a radius of 0.77 R ⊙ for HD 189733. Empirical and theoretical estimates of the host star’s radius are thus in excellent agreement, with a small error interval, thanks to the star’s position in a thin and slowly-evolving part of the lower main sequence and to the precision of the Hipparcos par- allax. In the subsequent analysis we combine the above esti- mates into R = 0.76 ± 0.01 R ⊙ and M = 0.82 ± 0.03 R ⊙ .

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