FeH Absorption in the Near-Infrared Spectra of Late M and L Dwarfs

We present medium-resolution z-, J-, and H-band spectra of four late-type dwarfs with spectral types ranging from M8 to L7.5. In an attempt to determine the origin of numerous weak absorption features throughout their near-infrared spectra, and motivated by the recent tentative identification of the E 4\Pi- A ^4\Pi system of FeH near 1.6 microns in umbral and cool star spectra, we have compared the dwarf spectra to a laboratory FeH emission spectrum. We have identified nearly 100 FeH absorption features in the z-, J-, and H-band spectra of the dwarfs. In particular, we have identified 34 features which dominate the appearance of the H-band spectra of the dwarfs and which appear in the laboratory FeH spectrum. Finally, all of the features are either weaker or absent in the spectrum of the L7.5 dwarf which is consistent with the weakening of the known FeH bandheads in the spectra of the latest L dwarfs.Comment: accepted by Ap

Modelling the molecular Zeeman effect in M-dwarfs: methods and first results

We present first quantitative results of the surface magnetic field measurements in selected M-dwarfs based on detailed spectra synthesis conducted simultaneously in atomic and molecular lines of the FeH Wing-Ford $F^4\,\Delta-X^4\,\Delta$ transitions. A modified version of the Molecular Zeeman Library (MZL) was used to compute Land\'e g-factors for FeH lines in different Hund's cases. Magnetic spectra synthesis was performed with the Synmast code. We show that the implementation of different Hund's case for FeH states depending on their quantum numbers allows us to achieve a good fit to the majority of lines in a sunspot spectrum in an automatic regime. Strong magnetic fields are confirmed via the modelling of atomic and FeH lines for three M-dwarfs YZ~CMi, EV~Lac, and AD~Leo, but their mean intensities are found to be systematically lower than previously reported. A much weaker field ($1.7-2$~kG against $2.7$~kG) is required to fit FeH lines in the spectra of GJ~1224. Our method allows us to measure average magnetic fields in very low-mass stars from polarized radiative transfer. The obtained results indicate that the fields reported in earlier works were probably overestimated by about $15-30$\%. Higher quality observations are needed for more definite results.Comment: Accepted by A&A, 13 pages, 7 figures, 1 tabl

First polarimetric observations and modeling of the FeH F^4 Delta-X^4 Delta system

Lines of diatomic molecules are more temperature and pressure sensitive than atomic lines, which makes them ideal tools for studying cool stellar atmospheres an internal structure of sunspots and starspots. The FeH F^4 Delta-X^4 Delta system represents such an example that exhibits in addition a large magnetic field sensitivity. The current theoretical descriptions of these transitions including the molecular constants involved are only based on intensity measurements because polarimetric observations have not been available so far, which limits their diagnostic value. We present for the first time spectropolarimetric observations of the FeH F^4 Delta-X^4 Delta system measured in sunspots to investigate their diagnostic capabilities for probing solar and stellar magnetic fields. We investigate whether the current theoretical model of FeH can reproduce the observed Stokes profiles including their magnetic properties. The polarimetric observations are compared with synthetic Stokes profiles modeled with radiative transfer calculations. This allows us to infer the temperature and the magnetic field strength of the observed sunspots. We find that the current theory successfully reproduces the magnetic properties of a large number of lines in the FeH F^4 Delta-X^4 Delta system. In a few cases the observations indicate a larger Zeeman splitting than predicted by the theory. There, our observations have provided additional constraints, which allowed us to determine empirical molecular constants. The FeH F^4 Delta-X^4 Delta system is found to be a very sensitive magnetic diagnostic tool. Polarimetric data of these lines provide us with more direct information to study the coolest parts of astrophysical objects.Comment: 4 pages, 3 figure

Carbon-Enhanced Metal-Poor Stars in the Inner and Outer Halo Components of the Milky Way

(Abridged) Carbon-enhanced metal-poor (CEMP) stars in the halo components of the Milky Way are explored, based on accurate determinations of the carbon-to-iron ([C/Fe]) abundance ratios and kinematic quantities for over 30000 calibration stars from the Sloan Digital Sky Survey (SDSS). Using our present criterion that low-metallicity stars exhibiting [C/Fe] ratios ("carbonicity") in excess of [C/Fe]$= +0.7$ are considered CEMP stars, the global frequency of CEMP stars in the halo system for \feh\ $< -1.5$ is 8%; for \feh\ $< -2.0$ it is 12%; for \feh\ $<-2.5$ it is 20%. We also confirm a significant increase in the level of carbon enrichment with declining metallicity, growing from $\sim +1.0$ at \feh\ $= -1.5$ to $\sim +1.7$ at \feh\ $= -2.7$. The nature of the carbonicity distribution function (CarDF) changes dramatically with increasing distance above the Galactic plane, $|$Z$|$. For $|$Z$|$ $< 5$ kpc, relatively few CEMP stars are identified. For distances $|$Z$|$ $> 5$ kpc, the CarDF exhibits a strong tail towards high values, up to [C/Fe] $>$ +3.0. We also find a clear increase in the CEMP frequency with $|$Z$|$. For stars with $-2.0 <$ [Fe/H] $< -$1.5, the frequency grows from 5% at $|$Z$|$ $\sim 2$ kpc to 10% at $|$Z$|$ $\sim 10$ kpc. For stars with [Fe/H] $< -$2.0, the frequency grows from 8% at $|$Z$|$ $\sim 2$ kpc to 25% at $|$Z$|$ $\sim 10$ kpc. For stars with $-2.0 <$ [Fe/H] $\sim +1.0$ for 0 kpc $<$ $|$Z$|$ $<$ 10 kpc, with little dependence on $|$Z$|$; for [Fe/H] $< -$2.0, $\sim +1.5$, again roughly independent of $|$Z$|$.Comment: Accepted for publication in the Astrophysical Journal, 32 pages, 15 figure

Molecules as magnetic probes of starspots

Stellar dynamo processes can be explored by measuring the magnetic field. This is usually obtained using the atomic and molecular Zeeman effect in spectral lines. While the atomic Zeeman effect can only access warmer regions, the use of molecular lines is of advantage for studying cool objects. The molecules MgH, TiO, CaH, and FeH are suited to probe stellar magnetic fields, each one for a different range of spectral types, by considering the signal that is obtained from modeling various spectral types. We have analyzed the usefulness of different molecules (MgH, TiO, CaH, and FeH) as diagnostic tools for studying stellar magnetism on active G-K-M dwarfs. We investigate the temperature range in which the selected molecules can serve as indicators for magnetic fields on highly active cool stars and present synthetic Stokes profiles for the modeled spectral type. We modeled a star with a spot size of 10% of the stellar disk and a spot comprising either only longitudinal or only transverse magnetic fields and estimated the strengths of the polarization Stokes V and Q signals for the molecules MgH, TiO, CaH, and FeH. We combined various photosphere and spot models according to realistic scenarios. In G dwarfs, the molecules MgH and FeH show overall the strongest Stokes V and Q signals from the starspot, whereas FeH has a stronger Stokes V signal in all G dwarfs, with a spot temperature of 3800K. In K dwarfs, CaH signals are generally stronger, and the TiO signature is most prominent in M dwarfs. Modeling synthetic polarization signals from starspots for a range of G-K-M dwarfs leads to differences in the prominence of various molecular signatures in different wavelength regions, which helps to efficiently select targets and exposure times for observations.Comment: 9 pages, 5 figures, 1 tabl

Exploring sugar metabolism in bread wheat for improving drought tolerance

Remobilization of stem WSC is well known to contribute to grain yield in wheat. There is, however, extensive genetic variation in the contribution of stem WSC to grain yield under post-anthesis water-deficit. Fructan 1-exohydrolase (1-FEH) is one of the major enzymes contributing to WSC remobilisation and the maintenance of grain yield under water-deficit. 1-FEH has three isoforms (1-FEH w1, w2 and w3) that degrade β - (2-1) fructan linkages thus contributing to fructan remobilization to grain. This thesis investigated the functional role of the three isoforms of the 1-FEH gene in WSC remobilisation under post anthesis water-deficit. Individual performance of the three isoforms was investigated using the corresponding isoform mutation lines derived from the Australian wheat variety Chara. Results from glasshouse experiments showed that the mutation of isoform 1-FEH w3 slowed down WSC remobilisation under post anthesis water-deficit and reduced grain filling and yield. In contrast, mutations of 1-FEH w1 and w2 did not affect WSC remobilisation under water-deficit. This means that 1-FEH w3 plays the leading functional role in WSC remobilisation during grain filling under water-deficit. This differences in remobilisation of WSC components between the mutation lines correlated with the expressional differences of the three isoforms of the 1-FEH gene across the lines. In the 1-FEH w3 mutation line, the expression of the other two isoforms (1-FEH w2 and w1) had the same level as the non-mutated parental cultivar Chara. However, in the 1-FEH w2 and w1 mutation lines, 1-FEH w3 showed significantly higher expression compared to Chara. The results indicated that the functional loss of the isoforms 1-FEH w2 and w1 was made up by the higher expression of the isoform 1-FEH w3 but the functional loss of the 1-FEH w3 isoform was not compensated by the other isoforms. This explains the ability of 1-FEH w2 and w1 mutation lines to maintain the same pattern of WSC remobilisation as the non-mutated parental cultivar. It was also, revealed that the expressional differences of the isforms of the 1-FEH gene across different mutation lines significantly influenced the degradation of WSC and its components under post anthesis water-deficit. Fructan, a fructose-based polymer synthesized from sucrose by fructosyltransferases (FTs), is the main component of wheat stem WSC and is a major source of sugar supply under post anthesis water-deficit when photosynthesis is reduced. Quick degradation of fructan is essential to remobilise sugar to developing grain under water-deficit and this is facilitated by FEHs. The 1-FEH w3 mutation line showed slower degradation and remobilization of fructan compared to the 1-FEH w2 and w1 mutation lines and Chara. This slow degradation made the 1-FEH w3 mutation line partially susceptible to post anthesis water-deficit. Noticeably, differences in WSC component degradation and gene expression of 1-FEH isoforms only became evident under post anthesis water-deficit and not in well-watered plants. This thesis also characterised the 1-FEH gene mutation, by mapping and annotating the mutated region. The F1 seeds, developed by back crossing the 1-FEH w1, w2 and w3 mutation lines with Chara, were genotyped using the Infinium 90K SNP iSelect platform. Putative deletions were identified in the FEH mutation lines encompassing the FEH genomic regions. A total of 15, 20 and 15SNPs were identified within the mutation regions of 1-FEH w1 w2, and w3, respectively. Mapping analysis demonstrated that the mutation affected significantly longer regions than the target gene regions of 1-FEH w1, w3 and w2. From the annotation of the mutation regions, 8 and 6 non-target genes were discovered on chromosomes 6A and 6B, respectively. The annotation of the 1-FEH w2 mutated region was complicated by the presence of an extra three copies of the gene on chromosome 6D. Functional roles of the non-target genes was carried out following computational biology approaches and confirmed that none of the affected non-target genes were expected to have a direct influence on 1-FEH gene function. This study also ratified the association of the distinct role of the 1-FEH w3 gene in sugar remobilisation to the developing wheat grain. Accumulation of oligosaccharides at two seed developmental stages were examined in the 1-FEH w3 mutation line in comparison to Chara under well-watered and water-deficit conditions. This study successfully overcome the challenge of preparing 25 μm seed sections by adopting cryosectioning using egg white which provided compatibility with the mass spectrometric equipment and enabled the production of ions from the oligosaccharides by the laser. Hexose and its polymers were detected separately by the mass spectrometry imaging (MSI) without any enzymatic digestion thus providing information regarding the localisation of sugar accumulation within the tissues of developing seeds. The abundance and localisation pattern of the identified oligosaccharides was influenced by the post anthesis water-deficit treatment. Under water-deficit, the mutation of the 1-FEH w3 reduced the abundance of oligosaccharide accumulation in two stages of seed development (17 DAA and 22 DAA) indicating it pivotal role under post anthesis water-deficit. This is the first study to use MSI to explore sugar accumulation directly within the tissue of developing seeds of wheat. This thesis established the individual role of three isoforms of 1-FEH in remobilising WSC under post anthesis water-deficit and provides unequivocal evidence that 1-FEH w3 is taking the most vital role. This new insight into the distinct role of the 1-FEH gene isoforms under post anthesis water-deficit should assist in providing new gene targets for water-deficit tolerant wheat breeding in the future

Line Intensities and Molecular Opacities of the FeH F4Δi−X4ΔiF^4\Delta_i-X^4\Delta_i Transition

We calculate new line lists and opacities for the $F^4\Delta_i-X^4\Delta_i$ transition of FeH. The 0-0 band of this transition is responsible for the Wing-Ford band seen in M-type stars, sunspots and brown dwarfs. The new Einstein A values for each line are based on a high level ab initio calculation of the electronic transition dipole moment. The necessary rotational line strength factors (H\"onl-London factors) are derived for both the Hund's case (a) and (b) coupling limits. A new set of spectroscopic constants were derived from the existing FeH term values for v=0, 1 and 2 levels of the $X$ and $F$ states. Using these constants extrapolated term values were generated for v=3 and 4 and for $J$ values up to 50.5. The line lists (including Einstein A values) for the 25 vibrational bands with v$\leq$4 were generated using a merged list of experimental and extrapolated term values. The FeH line lists were use to compute the molecular opacities for a range of temperatures and pressures encountered in L and M dwarf atmospheres. Good agreement was found between the computed and observed spectral energy distribution of the L5 dwarf 2MASS-1507.Comment: 52 pages, 3 figures, many tables, accepted for publication in the Astrophysical Journal Supplement