arXiv subjects

R. Schneider

Publications and source records attributed to R. Schneider.

At least 73 records · Page 4Linked to original sources

arXiv2017

The WISSH quasars Project: II. Giant star nurseries in hyper-luminous quasars

Studying the coupling between the energy output produced by the central quasar and the host galaxy is fundamental to fully understand galaxy evolution. Quasar feedback is indeed supposed to dramatically affect the galaxy properties by depositing large amounts of energy and momentum into the ISM. In order to gain further insights on this process, we study the SEDs of sources at the brightest end of the quasar luminosity function, for which the feedback mechanism is supposed to be at its maximum. We model the rest-frame UV-to-FIR SEDs of 16 WISE-SDSS Selected Hyper-luminous (WISSH) quasars at 1.8 < z < 4.6 disentangling the different emission components and deriving physical parameters of both the nuclear component and the host galaxy. We also use a radiative transfer code to account for the contribution of the quasar-related emission to the FIR fluxes. Most SEDs are well described by a standard combination of accretion disk+torus and cold dust emission. However, about 30% of them require an additional emission component in the NIR, with temperatures peaking at 750K, which indicates the presence of a hotter dust component in these powerful quasars. We measure extreme values of both AGN bolometric luminosity (LBOL > 10^47 erg/s) and SFR (up to 2000 Msun/yr). A new relation between quasar and star-formation luminosity is derived (LSF propto LQSO^(0.73)) by combining several Herschel-detected quasar samples from z=0 to 4. Future observations will be crucial to measure the molecular gas content in these systems, probe the impact between quasar-driven outflows and on-going star-formation, and reveal the presence of merger signatures in their host galaxies.

astro-ph.GA↗

arXiv2017

Anisotropic electronic transport of the two-dimensional electron system in Al2O3/SrTiO3 heterostructures

Transport measurements on the two dimensional electron system in Al2O3 SrTiO3 heterostructures indicate significant noncrystalline anisotropic behavior below T = 30 K. Lattice dislocations in SrTiO3 and interfacial steps are suggested to be the main sources for electronic anisotropy. Anisotropic defect scattering likewise alters magnetoresistance at low temperature remarkably and influences spin-orbit coupling significantly by the Elliot Yafet mechanism of spin relaxation resulting in anisotropic weak localization. Applying a magnetic field parallel to the interface results in an additional field induced anisotropy of the conductance, which can be attributed to Rashba spin orbit interaction. Compared to LaAlO3 SrTiO3, Rashba coupling seems to be reduced indicating a weaker polarity in Al2O3 SrTiO3 heterostructures.

cond-mat.str-el↗

arXiv2017

The history of the dark and luminous side of Milky Way-like progenitors

Here we investigate the evolution of a Milky Way (MW) -like galaxy with the aim of predicting the properties of its progenitors all the way from $z \sim 20$ to $z = 0$. We apply GAMESH (Graziani et al. 2015) to a high resolution N-Body simulation following the formation of a MW-type halo and we investigate its properties at $z \sim 0$ and its progenitors in $0 < z < 4$. Our model predicts the observed galaxy main sequence, the mass-metallicity and the fundamental plane of metallicity relations in $0 < z < 4$. It also reproduces the stellar mass evolution of candidate MW progenitors in $0 \lesssim z \lesssim 2.5$, although the star formation rate and gas fraction of the simulated galaxies follow a shallower redshift dependence. We find that while the MW star formation and chemical enrichment are dominated by the contribution of galaxies hosted in Lyman $α$-cooling halos, at z > 6 the contribution of star forming mini-halos is comparable to the star formation rate along the MW merger tree. These systems might then provide an important contribution in the early phases of reionization. A large number of mini-halos with old stellar populations, possibly Population~III stars, are dragged into the MW or survive in the Local Group. At low redshift dynamical effects, such as halo mergers, tidal stripping and halo disruption redistribute the baryonic properties among halo families. These results are critically discussed in light of future improvements including a more sophisticated treatment of radiative feedback and inhomogeneous metal enrichment.

astro-ph.GA↗

arXiv2017

AGB and SAGB stars: modelling dust production at solar metallicity

We present dust yields for asymptotic giant branch (AGB) and super--asymptotic giant branch (SAGB) stars of solar metallicity. Stars with initial mass $1.5~M_{\odot} \leq M_{\rm ini} \leq 3~M_{\odot}$ reach the carbon star stage during the AGB phase and produce mainly solid carbon and SiC. The size and the amount of the carbon particles formed follows a positive trend with themass of the star; the carbon grains with the largest size ($a_{\rm C} \sim 0.2μ$m) are produced by AGB stars with $M_{\rm ini} = 2.5-3~M_{\odot}$, as these stars are those achieving the largest enrichment of carbon in the surface regions. The size of SiC grains, being sensitive to the surface silicon abundance, keeps around $a_{\rm SiC} \sim 0.1μ$m. The mass of carbonaceous dust formed is in the range $10^{-4} - 5\times 10^{-3}~M_{\odot}$, whereas the amount of SiC produced is $2\times 10^{-4} - 10^{-3}~M_{\odot}$. Massive AGB/SAGB stars with $M_{\rm ini} > 3~M_{\odot}$ experience HBB, that inhibits formation of carbon stars. The most relevant dust species formed in these stars are silicates and alumina dust, with grain sizes in the range $0.1μm < a_{\rm ol} < 0.15μ$m and $a_{\rm Al_2O_3} \sim 0.07μ$m, respectively. The mass of silicates produced spans the interval $3.4\times 10^{-3}~M_{\odot} \leq M_{\rm dust} \leq 1.1\times 10^{-2}~M_{\odot}$ and increases with the initial mass of the star.

astro-ph.SR↗

arXiv2016

The WISSH Quasars Project I. Powerful ionised outflows in hyper-luminous quasars

Models and observations suggest that both power and effects of AGN feedback should be maximised in hyper-luminous (L_Bol>10^47 erg/s) quasars, i.e. objects at the brightest end of the AGN luminosity function. We present the first results of a multi-wavelength observing program, focusing on a sample of WISE/SDSS selected hyper-luminous (WISSH) broad-line quasars at z~1.5-5. The WISSH quasars project has been designed to reveal the most energetic AGN-driven outflows, estimate their occurrence at the peak of quasar activity and extend the study of correlations between outflows and nuclear properties up to poorly-investigated extreme AGN luminosities (L_Bol~10^47 -10^48 erg/s). We present NIR, long-slit LBT/LUCI1 spectroscopy of five WISSH quasars at z~2.3-3.5 showing prominent [OIII] emission lines with broad (FWHM~1200-2200 km/s) and skewed profiles. The luminosities of the broad [OIII] wings are the highest measured so far (L_[OIII]^broad >~5x10^44 erg/s) and reveal the presence of powerful ionised outflows with mass outflow rates Mdot >~1700 M_Sun/yr and kinetic powers Edot >~10^45 erg/s. Although these estimates are affected by large uncertainties, due to the use of [OIII] as tracer of ionized outflows and the very basic outflow model we assume, these results suggest that the AGN is highly efficient in pushing outwards large amounts of ionised gas in our targets. The mechanical outflow luminosities for WISSH quasars correspond to higher fractions (~1-3%) of L_Bol than those derived for lower L_Bol AGN. Our targets host very massive (M_BH>~2x10^9 M_Sun) black holes which are still accreting at a high rate (i.e. a factor of ~0.4-3 of the Eddington limit). These findings demonstrate that WISSH quasars offer the opportunity of probing the extreme end of both luminosity and SMBH mass functions and revealing powerful ionised outflows able to affect the evolution of their host galaxies.

astro-ph.GA↗

arXiv2016

Limits on Pop III star formation with the most iron-poor stars

We study the impact of star-forming mini-haloes, and the Initial Mass Function (IMF) of Population III (Pop III) stars, on the Galactic halo Metallicity Distribution Function (MDF) and on the properties of C-enhanced and C-normal stars at [Fe/H]<-3. For our investigation we use a data-constrained merger tree model for the Milky Way formation, which has been improved to self-consistently describe the physical processes regulating star-formation in mini-haloes, including the poor sampling of the Pop III IMF. We find that only when star-forming mini-haloes are included the low-Fe tail of the MDF is correctly reproduced, showing a plateau that is built up by C-enhanced metal-poor (CEMP) stars imprinted by primordial faint supernovae. The incomplete sampling of the Pop III IMF in inefficiently star-forming mini-haloes (< $10^{-3}$ $M_\odot$/yr) strongly limits the formation of Pair Instability Supernovae (PISNe), with progenitor masses $m_{\rm popIII}$=[140-260] $M_\odot$, even when a flat Pop III IMF is assumed. Second-generation stars formed in environments polluted at >50% level by PISNe are thus extremely rare, corresponding to $\approx$ 0.25% of the total stellar population at [Fe/H]<-2, which is consistent with recent observations. The low-Fe tail of the MDF strongly depends on the Pop III IMF shape and mass range. Given the current statistics, we find that a flat Pop III IMF model with $m_{\rm popIII}$=[10-300] $M_\odot$ is disfavoured by observations. We present testable predictions for Pop III stars extending down to lower masses, with $m_{\rm popIII}$=[0.1-300] $M_\odot$.

astro-ph.GA↗

arXiv2016

Patterning of two-dimensional electron systems in SrTiO3 based heterostructures using a CeO2 template

Two-dimensional electron systems found at the interface of SrTiO3-based oxide heterostructures often display anisotropic electric transport whose origin is currently under debate. To characterize transport along specific crystallographic directions, we developed a hard-mask patterning routine based on an amorphous CeO2 template layer. The technique allows preparing well-defined microbridges by conventional ultraviolet photolithography which, in comparison to standard techniques such as ion- or wet-chemical etching, does not induce any degradation of interfacial conductance. The patterning scheme is described in details and the successful production of microbridges based on amorphous Al2O3-SrTiO3 heterostructures is demonstrated. Significant anisotropic transport is observed for T < 30 K which is mainly related to impurity/defect scattering of charge carriers in these heterostructures.

cond-mat.str-el↗

arXiv2016

Dust grains from the heart of supernovae

Dust grains are classically thought to form in the winds of asymptotic giant branch (AGB) stars. However, there is increasing evidence today for dust formation in supernovae (SNe). To establish the relative importance of these two classes of stellar sources of dust, it is important to know the fraction of freshly formed dust in SN ejecta that is able to survive the passage of the reverse shock and be injected in the interstellar medium. We have developed a new code (GRASH\_Rev) which follows the newly-formed dust evolution throughout the supernova explosion until the merging of the forward shock with the circumstellar ISM. We have considered four well studied SNe in the Milky Way and Large Magellanic Cloud: SN1987A, CasA, the Crab Nebula, and N49. For all the simulated models, we find good agreement with observations and estimate that between 1 and 8$\%$ of the observed mass will survive, leading to a SN dust production rate of $(3.9 \pm 3.7) \times 10^{-4}$ M$_{\odot}$yr$^{-1}$ in the Milky Way. This value is one order of magnitude larger than the dust production rate by AGB stars but insufficient to counterbalance the dust destruction by SNe, therefore requiring dust accretion in the gas phase.

astro-ph.HE↗

arXiv2016

Fast outflows and star formation quenching in quasar host galaxies

Negative feedback from active galactic nuclei (AGN) is considered a key mechanism in shaping galaxy evolution. Fast, extended outflows are frequently detected in the AGN host galaxies at all redshifts and luminosities, both in ionised and molecular gas. However, these outflows are only "potentially" able to quench star formation and we are still missing a decisive evidence of negative feedback in action. Here we present Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) H- and K-band integral-field spectroscopic observations of two quasars at $z\sim$2.4 characterised by fast, extended outflows detected through the [OIII]$λ$5007 line (Carniani et al. 2015). The high signal-to-noise ratio of our observations allows us to identify faint narrow (FWHM $< 500$ km/s), and spatially extended components in [OIII]$λ$5007 and H$α$ emission associated with star formation in the host galaxy. Such star-formation powered emission is spatially anti-correlated with the fast outflows. The ionised outflows therefore appear to be able to suppress star formation in the region where the outflow is expanding. However the detection of narrow, spatially-extended H$α$ emission indicates star formation rates of at least $\sim 50-90$ M$_{\odot}$/yr, suggesting either that AGN feedback does not affect the whole galaxy or that many feedback episodes are required before star formation is completely quenched. On the other hand, the narrow H$α$ emission extending along the edges of the outflow cone may lead also to a positive feedback interpretation. Our results highlight the possible twofold role of galaxy-wide outflows in host galaxy evolution.

astro-ph.GA↗

arXiv2016

Dust grains from the heart of supernovae

Dust grains are classically thought to form in the winds of AGB stars. However, nowadays there is increasing evidence for dust formation in SNe. In order to establish the relative importance of these two classes of stellar sources of dust it is important to know what is the fraction of freshly formed dust in SN ejecta that is able to survive the passage of the reverse shock and be injected in the interstellar medium. With this aim, we have developed a new code, GRASH_Rev, that allows to follow the dynamics of dust grains in the shocked SN ejecta and to compute the time evolution of the mass, composition and size distribution of the grains. We consider four well studied SNe in the Milky Way and LMC: SN 1987a, Cas A, the Crab Nebula, and N49. For all the simulated models, we find good agreement with observations. Our study suggests that SN 1987A is too young for the reverse shock to have affected the dust mass. Conversely, in the other three SNe, the reverse shock has already destroyed between 10 and 40% of the initial dust mass. However, the largest dust mass destruction is predicted to occur between 10^3 and 10^5 yr after the explosions. Since the oldest SN in the sample has an estimated age of 4800 yr, current observations can only provide an upper limit to the mass of SN dust that will enrich the interstellar medium, the so-called effective dust yields. We find that only between 1 and 8% of the currently observed mass will survive. This is in good agreement with the values adopted in chemical evolution models which consider the effect of the SN reverse shock. We discuss the astrophysical implications of our results for dust enrichment in local galaxies and at high redshift.

astro-ph.HE↗

arXiv2015

Thin-film based phase plates for transmission electron microscopy fabricated from metallic glasses

Thin-film based phase plates are meanwhile a widespread tool to enhance the contrast of weak-phase objects in transmission electron microscopy (TEM). The thin film usually consists of amorphous carbon, which suffers from quick degeneration under the intense electron-beam illumination. Recent investigations have focused on the search for alternative materials with an improved material stability. This work presents thin-film based phase plates fabricated from metallic glass alloys, which are characterized by a high electrical conductivity and an amorphous structure. Thin films of the zirconium-based alloy Zr65.0Al7.5Cu27.5 (ZAC) are prepared and their phase-shifting properties are tested. The ZAC-alloy film is investigated by different TEM techniques, which reveal a range of beneficial characteristics. Particularly favorable is the small probability for inelastic plasmon scattering, which is promising to improve the performance of thin-film based phase plates in phase-contrast TEM.

cond-mat.mtrl-sci↗

arXiv2015

AGB stars in the SMC: evolution and dust properties based on Spitzer observations

We study the population of asymptotic giant branch (AGB) stars in the Small Magellanic Cloud (SMC) by means of full evolutionary models of stars of mass 1Msun < M < 8Msun, evolved through the thermally pulsing phase. The models also account for dust production in the circumstellar envelope. We compare Spitzer infrared colours with results from theoretical modelling. We show that ~75% of the AGB population of the SMC is composed by scarcely obscured objects, mainly stars of mass M < 2.5Msun at various metallicity, formed between 700 Myr and 5 Gyr ago; ~ 70% of these sources are oxygen--rich stars, while ~ 30% are C-stars. The sample of the most obscured AGB stars, accounting for ~ 25% of the total sample, is composed almost entirely by carbon stars. The distribution in the colour-colour ([3.6]-[4.5], [5.8]-[8.0]) and colour-magnitude ([3.6]-[8.0], [8.0]) diagrams of these C-rich objects, with a large infrared emission, traces an obscuration sequence, according to the amount of carbonaceous dust in their surroundings. The overall population of C-rich AGB stars descends from 1.5-2Msun stars of metallicity Z=0.004, formed between 700 Myr and 2 Gyr ago, and from lower metallicity objects, of mass below 1.5Msun, 2-5 Gyr old. We also identify obscured oxygen-rich stars (M ~ 4-6Msun) experiencing hot bottom burning. The differences between the AGB populations of the SMC and LMC are also commented.

astro-ph.SR↗

arXiv2015

The metal and dust yields of the first massive stars

We quantify the role of Population (Pop) III core-collapse supernovae (SNe) as the first cosmic dust polluters. Starting from a homogeneous set of stellar progenitors with masses in the range [13 - 80] Msun, we find that the mass and composition of newly formed dust depend on the mixing efficiency of the ejecta and the degree of fallback experienced during the explosion. For standard Pop III SNe, whose explosions are calibrated to reproduce the average elemental abundances of Galactic halo stars with [Fe/H] < -2.5, between 0.18 and 3.1 Msun (0.39 - 1.76 Msun) of dust can form in uniformly mixed (unmixed) ejecta, and the dominant grain species are silicates. We also investigate dust formation in the ejecta of faint Pop III SN, where the ejecta experience a strong fallback. By examining a set of models, tailored to minimize the scatter with the abundances of carbon-enhanced Galactic halo stars with [Fe/H ] < -4, we find that amorphous carbon is the only grain species that forms, with masses in the range 2.7 10^{-3} - 0.27 Msun (7.5 10^{-4} - 0.11 Msun) for uniformly mixed (unmixed) ejecta models. Finally, for all the models we estimate the amount and composition of dust that survives the passage of the reverse shock, and find that, depending on circumstellar medium densities, between 3 and 50% (10 - 80%) of dust produced by standard (faint) Pop III SNe can contribute to early dust enrichment.

astro-ph.GA↗

arXiv2015

Halo dust detection around NGC 891

Observations of edge-on galaxies allow us to investigate the vertical extent and properties of dust, gas and stellar distributions. NGC 891 has been studied for decades and represents one of the best studied cases of an edge-on galaxy. We use deep PACS data together with IRAC, MIPS and SPIRE data to study the vertical extent of dust emission around NGC 891. We also test the presence of a more extended, thick dust component. By performing a convolution of an intrinsic vertical profile emission with each instrument PSF and comparing it with observations we derived the scaleheight of a thin and thick dust disc component. For all wavelengths considered the emission is best fit with the sum of a thin and a thick dust component. The scaleheight of both dust components shows a gradient passing from 70 $μ$m to 250 $μ$m. This could be due to a drop in dust heating (and thus dust temperature) with the distance from the plane, or to a sizable contribution ($\sim 15 - 80%$) of an unresolved thin disc of hotter dust to the observed surface brightness at shorter wavelengths. The scaleheight of the thick dust component, using observations from 70 $μ$m to 250 $μ$m has been estimated to be $(1.44\pm 0.12)$ kpc, consistent with previous estimates (extinction and scattering in optical bands and MIR emission). The amount of dust mass at distances larger than $\sim 2$ kpc from the midplane represents $2 - 3.3$ % of the total galactic dust mass and the relative abundance of small grains with respect to large grains is almost halved comparing to that in the midplane. The paucity of small grains high above the midplane might indicate that dust is hit by interstellar shocks or galactic fountains and entrained together with gas. The halo dust component is likely to be embedded in an atomic / molecular gas and heated by a thick stellar disc.

astro-ph.GA↗

arXiv2015

The Brightest Ly$α$ Emitter: Pop III or Black Hole?

CR7 is the brightest $z=6.6 \, {\rm Ly}α$ emitter (LAE) known to date, and spectroscopic follow-up by Sobral et al. (2015) suggests that CR7 might host Population (Pop) III stars. We examine this interpretation using cosmological hydrodynamical simulations. Several simulated galaxies show the same "Pop III wave" pattern observed in CR7. However, to reproduce the extreme CR7 ${\rm Ly}α$/HeII1640 line luminosities ($L_{\rm α/He II}$) a top-heavy IMF and a massive ($>10^{7}{\rm M}_{\odot}$) PopIII burst with age $<2$ Myr are required. Assuming that the observed properties of ${\rm Ly}α$ and HeII emission are typical for Pop III, we predict that in the COSMOS/UDS/SA22 fields, 14 out of the 30 LAEs at $z=6.6$ with $L_α >10^{43.3}{\rm erg}\,{\rm s}^{-1}$ should also host Pop III stars producing an observable $L_{\rm He II}>10^{42.7}{\rm erg}\,{\rm s}^{-1}$. As an alternate explanation, we explore the possibility that CR7 is instead powered by accretion onto a Direct Collapse Black Hole (DCBH). Our model predicts $L_α$, $L_{\rm He II}$, and X-ray luminosities that are in agreement with the observations. In any case, the observed properties of CR7 indicate that this galaxy is most likely powered by sources formed from pristine gas. We propose that further X-ray observations can distinguish between the two above scenarios.

astro-ph.GA↗

arXiv2015

Ionised outflows in z $\sim$ 2.4 quasar host galaxies

AGN-driven outflows are invoked by galaxy evolutionary models to quench star formation and to explain the origin of the relations observed locally between super massive black holes and their host galaxies. This work aims to detect the presence of extended ionised outflows in luminous quasars where we expect the maximum activity both in star formation and in black hole accretion. Currently, there are only a few studies based on spatially resolved observations of outflows at high redshift, $z>2$. We analyse a sample of six luminous (${\rm L>10^{47} \ erg/s}$) quasars at $z\sim2.4$, observed in H-band using the near-IR integral field spectrometer SINFONI at VLT. We perform a kinematic analysis of the [OIII] emission line at $λ= 5007Å$. [OIII] has a complex gas kinematic, with blue-shifted velocities of a few hundreds of km/s and line widths up to 1500 km/s. Using the spectroastrometric method we infer size of the ionised outflows of up to $\sim$2 kpc. The properties of the ionised outflows, mass outflow rate, momentum rate and kinetic power, are correlated with the AGN luminosity. The increase in outflow rate with increasing AGN luminosity is consistent with the idea that a luminous AGN pushes away the surrounding gas through fast outflows driven by radiation pressure, which depends on the emitted luminosity. We derive mass outflow rates of about 6-700 M$_{\odot}$/yr for our sample, which are lower than those observed in molecular outflows. Indeed physical properties of ionised outflows show dependences on AGN luminosity which are similar to those of molecular outflows but indicating that the mass of ionised gas is smaller than that of the molecular one. Alternatively, this discrepancy between ionised and molecular outflows could be explained with different acceleration mechanisms.

astro-ph.GA↗

arXiv2015

The Cosmic Dawn and Epoch of Reionization with the Square Kilometre Array

Concerted effort is currently ongoing to open up the Epoch of Reionization (EoR) ($z\sim$15-6) for studies with IR and radio telescopes. Whereas IR detections have been made of sources (Lyman-$α$ emitters, quasars and drop-outs) in this redshift regime in relatively small fields of view, no direct detection of neutral hydrogen, via the redshifted 21-cm line, has yet been established. Such a direct detection is expected in the coming years, with ongoing surveys, and could open up the entire universe from $z\sim$6-200 for astrophysical and cosmological studies, opening not only the EoR, but also its preceding Cosmic Dawn ($z\sim$30-15) and possibly even the later phases of the Dark Ages ($z\sim$200-30). All currently ongoing experiments attempt statistical detections of the 21-cm signal during the EoR, with limited signal-to-noise. Direct imaging, except maybe on the largest (degree) scales at lower redshifts, as well as higher redshifts will remain out of reach. The Square Kilometre Array(SKA) will revolutionize the field, allowing direct imaging of neutral hydrogen from scales of arc-minutes to degrees over most of the redshift range $z\sim$6-28 with SKA1-LOW, and possibly even higher redshifts with the SKA2-LOW. In this SKA will be unique, and in parallel provide enormous potential of synergy with other upcoming facilities (e.g. JWST). In this chapter we summarize the physics of 21-cm emission, the different phases the universe is thought to go through, and the observables that the SKA can probe, referring where needed to detailed chapters in this volume (Abridged).

astro-ph.CO↗

arXiv2015

The Large Magellanic Cloud as a laboratory for Hot Bottom Burning in massive Asymptotic Giant Branch stars

We use Spitzer observations of the rich population of Asymptotic Giant Branch stars in the Large Magellanic Cloud (LMC) to test models describing the internal structure and nucleosynthesis of the most massive of these stars, i.e. those with initial mass above $\sim 4M_{\odot}$. To this aim, we compare Spitzer observations of LMC stars with the theoretical tracks of Asymptotic Giant Branch models, calculated with two of the most popular evolution codes, that are known to differ in particular for the treatment of convection. Although the physical evolution of the two models are significantly different, the properties of dust formed in their winds are surprisingly similar, as is their position in the colour-colour (CCD) and colour-magnitude (CMD) diagrams obtained with the Spitzer bands. This model independent result allows us to select a well defined region in the ($[3.6]-[4.5], [5.8]-[8.0]$) plane, populated by AGB stars experiencing Hot Bottom Burning, the progeny of stars with mass $M\sim 5.5M_{\odot}$. This result opens up an important test of the strength hot bottom burning using detailed near-IR (H and K bands) spectroscopic analysis of the oxygen-rich, high luminosity candidates found in the well defined region of the colour-colour plane. This test is possible because the two stellar evolution codes we use predict very different results for the surface chemistry, and the C/O ratio in particular, owing to their treatment of convection in the envelope and of convective boundaries during third dredge-up. The differences in surface chemistry are most apparent when the model stars reach the phase with the largest infrared emission.

astro-ph.SR↗