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

Democracy Takes Another Step Forward in #GhanaDecides 2016

Kafui Tsekpo and Alexander Afram analyse the implications behind the 2016 general elections in Ghana

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

A comparison of measured and simulated solar network contrast

Long-term trends in the solar spectral irradiance are important to determine the impact on Earth's climate. These long-term changes are thought to be caused mainly by changes in the surface area covered by small-scale magnetic elements. The direct measurement of the contrast to determine the impact of these small-scale magnetic elements is, however, limited to a few wavelengths, and is, even for space instruments, affected by scattered light and instrument defocus. In this work we calculate emergent intensities from 3-D simulations of solar magneto-convection and validate the outcome by comparing with observations from Hinode/SOT. In this manner we aim to construct the contrast at wavelengths ranging from the NUV to the FIR.Comment: Proceedings paper, IAU XXVII, Symposium 264, 3 page

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

Rotation, magnetism, and metallicity of M dwarf systems

Close M-dwarf binaries and higher multiples allow the investigation of rotational evolution and mean magnetic flux unbiased from scatter in inclination angle and age since the orientation of the spin axis of the components is most likely parallel and the individual systems are coeval. Systems composed of an early (M0.0 -- M4.0) and a late (M4.0 -- M8.0) type component offer the possibility to study differences in rotation and magnetism between partially and fully convective stars. We have selected 10 of the closest dM systems to determine the rotation velocities and the mean magnetic field strengths based on spectroscopic analysis of FeH lines of Wing-Ford transitions at 1 $\mu$m observed with VLT/CRIRES. We also studied the quality of our spectroscopic model regarding atmospheric parameters including metallicity. A modified version of the Molecular Zeeman Library (MZL) was used to compute Land\'e g-factors for FeH lines. Magnetic spectral synthesis was performed with the Synmast code. We confirmed previously reported findings that less massive M-dwarfs are braked less effectively than objects of earlier types. Strong surface magnetic fields were detected in primaries of four systems (GJ 852, GJ 234, LP 717-36, GJ 3322), and in the secondary of the triple system GJ 852. We also confirm strong 2 kG magnetic field in the primary of the triple system GJ 2005. No fields could be accurately determined in rapidly rotating stars with \vsini>10 \kms. For slow and moderately rotating stars we find the surface magnetic field strength to increase with the rotational velocity \vsini which is consistent with other results from studying field stars.Comment: Accepted by MNRAS, 10 pages, 4 figures, 4 table

Common Causes of Leakages in Parapet Roof Construction in Ghana: A Case Study from Kumasi

In Ghana, especially Kumasi, the second largest city after Accra, the country\'s capital, parapet roof construction became fashionable in building construction in the 1970\'s. It entailed hiding the roofs of buildings from view behind parapet walls. This concept is popularly known as “Bohyemu”, literally meaning “construct it inside\'” or more appropriately “hide it in”. The paper examines roof designs and their functional requirements in general and specifically discusses problems associated with parapet roof construction in the country, with particular reference to Kumasi. It outlines some examples of such roofing and their respective problem areas, which include design and poor detailing, and offers practical suggestions that may help in arresting these problems. The paper concludes by sounding a note of caution to technocrats in the building profession to be more diligent in the detailing, construction and supervision of this type of roof, as well as “diagnosing” problems of leakages associated with parapet roofs, since they are usually caused by a plethora of factors which, if not well-considered and assessed, may ultimately lead to the wrong “prescriptions” in trying to in solve them. Keywords: Parapet, Roof Design, Roof Leakage, Construction Journal of Science & Technology (Ghana) Vol. 28 (3) 2008: pp. 123-13