The Solar Neighborhood Complete Survey of Stars and Planets Orbiting K Stars

Here I present a comprehensive study of the multiplicity of a volume-complete sample of K stars within 33 pc, a part RECONS K Star project (RKS), a large effort with the objective of searching for stellar, substellar, and planetary companions using three observational techniques to cover separations from 10 000 AU to 0.1 AU. In this work, I present the results of the companion search for 804 K dwarf type stars using the radial velocity (RV) technique. The survey extends for five years so far using the CHIRON Spectrograph at the CTIO/SMARTS 1.5m, achieving precisions down to 7 m/s for K dwarfs with V magnitudes between 7.0-11.5. Of the 804 K dwarfs within 33 pc and between DEC +30o and -30o, a sample of 562 K dwarfs did not have high precision RV measurements before, and are now the target of our volume-complete survey. Among the 804 stars we have found 124 RV perturbations consistent with companions never detected before, of which 38 are newly discovered stellar/sub-stellar orbits, 4 are likely planet candidates, and 82 are strong candidates for companions. Combining these results with known companions, we present here a detailed portrait of K dwarf systems unveiling a stellar multiplicity fraction of 22%, when only RV surveys are considered. The results remain consistent between the 25 pc and 33 pc, even when the 33 pc is almost doubling the stars in the 25 pc sample. The orbital architectures given by RVs and presented here, show that the lack of brown dwarfs in short period regimes still applies, and shows circular orbits become more rare with increasing orbital period. All of which starts to provide insights into formation processes around K stars. Ultimately, by providing a careful defined sample, a systematic search, and the combination of previous studies, this thesis research aims to set basis for understanding star and planet formation processes for decades to come

Ising Model Partition Function Computation as a Weighted Counting Problem

While the Ising model remains essential to understand physical phenomena, its natural connection to combinatorial reasoning makes it also one of the best models to probe complex systems in science and engineering. We bring a computational lens to the study of Ising models, where our computer-science perspective is two-fold: On the one hand, we consider the computational complexity of the Ising partition-function problem, or #Ising, and relate it to the logic-based counting of constraint-satisfaction problems, or #CSP. We show that known dichotomy results for #CSP give an easy proof of the hardness of #Ising and provide new intuition on where the difficulty of #Ising comes from. On the other hand, we also show that #Ising can be reduced to Weighted Model Counting (WMC). This enables us to take off-the-shelf model counters and apply them to #Ising. We show that this WMC approach outperforms state-of-the-art specialized tools for #Ising, thereby expanding the range of solvable problems in computational physics.Comment: 16 pages, 2 figure

Mind the Gap I: Hα\alpha Activity of M Dwarfs Near the Partially/Fully Convective Boundary and a New Hα\alpha Emission Deficiency Zone on the Main Sequence

Since identifying the gap in the H-R Diagram (HRD) marking the transition between partially and fully convective interiors, a unique type of slowly pulsating M dwarf has been proposed. These unstable M dwarfs provide new laboratories in which to understand how changing interior structures result in potentially observable activity at the surface. In this work, we report the results of the largest high-resolution spectroscopic H$\alpha$ emission survey to date spanning this transition region, including 480 M dwarfs observed using the CHIRON spectrograph at CTIO/SMARTS 1.5-m. We find that M dwarfs with H$\alpha$ in emission are almost entirely found 0 to 0.5 magnitude above the top edge of the gap in the HRD, whereas effectively no stars in and below the gap show emission. Thus, the top edge of the gap marks a relatively sharp activity transition and there is no anomalous H$\alpha$ activity for stars in the gap. We also identify a new region at 10.3 $<M_{G}<$ 10.8 on the main sequence where fewer M dwarfs exhibit H$\alpha$ emission compared to M dwarfs above and below this magnitude range. Careful evaluation of literature results indicates that 1) rotation and H$\alpha$ activity distributions on the main sequence are closely related, and 2) fewer stars in this absolute magnitude range rotate in less than $\sim$13 days than populations surrounding this region. This result suggests that the most massive fully convective stars lose their angular momentum faster than both partially convective stars and less massive fully convective stars.Comment: 30 pages, 18 figures, and 6 table. Submitted to A

MASCARA-4 b/bRing-1 b: A retrograde hot Jupiter around a bright A-type star

Context. The Multi-site All-Sky CAmeRA (MASCARA) and bRing are both photometric ground-based instruments with multiple stations that rely on interline charge-coupled devices with wide-field lenses to monitor bright stars in the local sky for variability. MASCARA has already discovered several planets in the northern sky, which are among the brightest known transiting hot Jupiter systems. Aims. In this paper, we aim to characterize a transiting planetary candidate in the southern skies found in the combined MASCARA and bRing data sets of HD 85628, an A7V star of V = 8.2 mag at a distance 172 pc, to establish its planetary nature. Methods. The candidate was originally detected in data obtained jointly with the MASCARA and bRing instruments using a Box Least-Square search for transit events. Further photometry was taken by the 0.7 m Chilean-Hungarian Automated Telescope (CHAT), and radial velocity measurements with the Fiber Dual Echelle Optical Spectrograph on the European Southern Observatory 1.0 m Telescope. High-resolution spectra during a transit were taken with the CTIO high-resolution spectrometer (CHIRON) on the Small and Moderate Aperture Research Telescope System 1.5 m telescope to target the Doppler shadow of the candidate. Results. We confirm the existence of a hot Jupiter transiting the bright A7V star HD 85628, which we co-designate as MASCARA-4b and bRing-1b. It is in an orbit of 2.824 days, with an estimated planet radius of 1.53−0.04+0.07 RJup and an estimated planet mass of 3.1 +- 0.9 MJup, putting it well within the planetary regime. The CHAT observations show a partial transit, reducing the probability that the transit was around a faint background star. The CHIRON observations show a clear Doppler shadow, implying that the transiting object is in a retrograde orbit with |λ| =244.9−3.6+2.7◦. The planet orbits at a distance of 0.047 +- 0.004 AU from the star and has a zero-albedo equilibrium temperature of 2100 +- 100 K. In addition, we find that HD 85628 has a previously unreported stellar companion star in the Gaia DR2 data demonstrating common proper motion and parallax at 4.3′′ separation (projected separation ~740 AU), and with absolute magnitude consistent with being a K/M dwarf. Conclusions. MASCARA-4 b/bRing-1 b is the brightest transiting hot Jupiter known to date in a retrograde orbit. It further confirms that planets in near-polar and retrograde orbits are more common around early-type stars. Due to its high apparent brightness and short orbital period, the system is particularly well suited for further atmospheric characterization.I.S. acknowledges support from a NWO VICI grant (639.043.107). This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement nr. 694513). E.E.M. and S.N.M. acknowledge support from the NASA NExSS programme. SNM is a US Department of Defense SMART scholar sponsored by the U.S. Navy through NIWC-Atlantic. E.E.M. acknowledges support from the NASA NExSS program and a JPL RT&D award. A.W. acknowledges the support of the SNSF by the grant number P2GEP2 178191. L.V. acknowledges the support of CONICYT Project Fondecyt n. 1171364

Gestión financiera y competitividad en Establecimientos de Hospedaje en la Región Junín

The objective of determine the statistical conclusion between financial management and competitiveness in lodging establishments in the Junín region. The methodology used was a quantitative approach, basic type, correlational level and non-experimental design. To determine the population and sample, the non-probabilistic documentation was applied for convenience in order to be able to access it more easily. Questionnaires with polytomous answers and processing of these in Excel and SPSS were applied. As a result, a medium-low positive confirmation of 0.212, but statistically significant between the two variables, in terms of the dimensions of financial management and the competitiveness variable, relationships were obtained between low and high and equally statistically significant, thus verifying what was proposed in the research. Finally, it can be concluded that applying a certain use of financial management such as financial statements, use of accounting records, among others, affects competitiveness since this variable is carried out based on the human factor and the company's own resources, which generate the activities for your organization. According to the results obtained, among the most significant we have financial analysis and control, obtaining 70% and 76.7% of good management.El objetivo fue determinar la correlación estadística entre gestión financiera y competitividad en establecimientos de hospedaje en la región Junín. La metodología utilizada fue de enfoque cuantitativo, tipo básico, nivel correlacional y diseño no experimental. Para determinar la población y muestra se aplicó el muestreo no probabilístico por conveniencia con el fin de poder acceder con mayor facilidad a esta. Se aplicó cuestionarios con respuestas politómicas y procesamiento de estas en Excel y SPSS. Como resultado se determinó una fuerza de correlación estadística positiva media-baja de 0,212, pero estadísticamente significativas, con p-valor menor a 0,005 entre ambas variables, en cuanto a las dimensiones de gestión financiera y la variable competitividad se obtuvo relaciones entre bajas y altas, pero igualmente estadísticamente significativas comprobando de esta manera lo propuesto en la investigación. Por ende, se puede concluir que aplicar determinado uso de gestión financiera como estados financieros, uso de registros contables, entre otros, incide en la competitividad ya que esta variable se realiza en base al factor humano y recursos propios de la empresa las cuales generan las actividades favor de su organización. De acuerdo con los resultados obtenidos, entre los más significativos tenemos al análisis y control financiero obteniendo un 70 % y 76.7 % de buena gestión

TESS Discovery of an ultra-short-period planet around the nearby M dwarf LHS 3844

Data from the newly-commissioned \textit{Transiting Exoplanet Survey Satellite} (TESS) has revealed a "hot Earth" around LHS 3844, an M dwarf located 15 pc away. The planet has a radius of $1.32\pm 0.02$ $R_\oplus$ and orbits the star every 11 hours. Although the existence of an atmosphere around such a strongly irradiated planet is questionable, the star is bright enough ($I=11.9$, $K=9.1$) for this possibility to be investigated with transit and occultation spectroscopy. The star's brightness and the planet's short period will also facilitate the measurement of the planet's mass through Doppler spectroscopy.Comment: 10 pages, 4 figures. Submitted to ApJ Letters. This letter makes use of the TESS Alert data, which is currently in a beta test phase, using data from the pipelines at the TESS Science Office and at the TESS Science Processing Operations Cente

Observation of Pulsed Gamma-rays Above 25 GeV from the Crab Pulsar with MAGIC

One fundamental question about pulsars concerns the mechanism of their pulsed electromagnetic emission. Measuring the high-end region of a pulsar's spectrum would shed light on this question. By developing a new electronic trigger, we lowered the threshold of the Major Atmospheric gamma-ray Imaging Cherenkov (MAGIC) telescope to 25 GeV. In this configuration, we detected pulsed gamma-rays from the Crab pulsar that were greater than 25 GeV, revealing a relatively high cutoff energy in the phase-averaged spectrum. This indicates that the emission occurs far out in the magnetosphere, hence excluding the polar-cap scenario as a possible explanation of our measurement. The high cutoff energy also challenges the slot-gap scenario.Comment: Slight modification of the analysis: Fitting a more general function to the combined data set of COMPTEL, EGRET and MAGIC. Final result and conclusion is unchange

First bounds on the high-energy emission from isolated Wolf-Rayet binary systems

High-energy gamma-ray emission is theoretically expected to arise in tight binary star systems (with high mass loss and high velocity winds), although the evidence of this relationship has proven to be elusive so far. Here we present the first bounds on this putative emission from isolated Wolf-Rayet (WR) star binaries, WR 147 and WR 146, obtained from observations with the MAGIC telescope.Comment: (Authors are the MAGIC Collaboration.) Manuscript in press at The Astrophysical Journal Letter

MAGIC Upper Limits for two Milagro-detected, Bright Fermi Sources in the Region of SNR G65.1+0.6

We report on the observation of the region around supernova remnant G65.1+0.6 with the stand-alone MAGIC-I telescope. This region hosts the two bright GeV gamma-ray sources 1FGL J1954.3+2836 and 1FGL J1958.6+2845. They are identified as GeV pulsars and both have a possible counterpart detected at about 35 TeV by the Milagro observatory. MAGIC collected 25.5 hours of good quality data, and found no significant emission in the range around 1 TeV. We therefore report differential flux upper limits, assuming the emission to be point-like (<0.1 deg) or within a radius of 0.3 deg. In the point-like scenario, the flux limits around 1 TeV are at the level of 3 % and 2 % of the Crab Nebula flux, for the two sources respectively. This implies that the Milagro emission is either extended over a much larger area than our point spread function, or it must be peaked at energies beyond 1 TeV, resulting in a photon index harder than 2.2 in the TeV band.Comment: 8 pages, 3 figures, 1 tabl