Searches for planetary transits find many astrophysical false positives as a by-product. There are four main types analyzed in the literature: a grazing-incidence eclipsing binary star, an eclipsing binary star with a small radius companion star, a blend of one or more stars with an unrelated eclipsing binary star, and a physical triple star system. We present a list of 69 astrophysical false positives that had been identified as candidates of transiting planets of the on-going XO survey. This list may be useful in order to avoid redundant observation and characterization of these particular candidates independently identified by other wide-field searches for transiting planets. The list may be useful for those modeling the yield of the XO survey and surveys similar to it. Subsequent observations of some of the listed stars may improve mass-radius relations, especially for low-mass stars. From the candidates exhibiting eclipses, we report three new spectroscopic double-line binaries and give mass function estimations for 15 single lined spectroscopic binaries.
With the discovery of hundreds of exoplanets and a potentially huge number of Earth-like planets waiting to be discovered, the conditions for their habitability have become a focal point in exoplanetary research. The classical picture of habitable zones primarily relies on the stellar flux allowing liquid water to exist on the surface of an Earth-like planet with a suitable atmosphere. However, numerous further stellar and planetary properties constrain habitability. Apart from "geophysical" processes depending on the internal structure and composition of a planet, a complex array of astrophys…
The faint young Sun paradox remains an open question. Presented here is one possible solution to this apparent inconsistency, a more massive early Sun. Based on conditions on early Earth and Mars, a luminosity constraint is set as a function of mass. We examine helioseismic constraints of these alternative mass-losing models. Additionally, we explore a dynamic electron screening correction in an effort to improve helioseismic agreement in the core of the an early mass-losing model.
The German Astrophysical Virtual Observatory (GAVO) developed the registered service TheoSSA (theoretical stellar spectra access) and the supporting registered VO tool TMAW (Tuebingen Model-Atmosphere WWW interface). These allow individual spectral analyses of hot, compact stars with state-of-the-art non-local thermodynamical equilibrium (NLTE) stellar-atmosphere models that presently consider opacities of the elements H, He, C, N, O, Ne, Na, and Mg, without requiring detailed knowledge about the involved background codes and procedures. Presently, TheoSSA provides easy access to about 150000 …
We investigate in this paper the astrophysical false-positive configuration in exoplanet-transit surveys that involves eclipsing binaries and giant planets which present only a secondary eclipse, as seen from the Earth. To test how an eclipsing binary configuration can mimic a planetary transit, we generate synthetic light curve of three examples of secondary-only eclipsing binary systems that we fit with a circular planetary model. Then, to evaluate its occurrence we model a population of binaries in double and triple system based on binary statistics and occurrence. We find that 0.061% +/- 0…
In this review/tutorial we explore planetary nebulae as a stage in the evolution of low-to-intermediate-mass stars, as major contributors to the mass and chemical enrichment of the interstellar medium, and as astrophysical laboratories. We discuss many observed properties of planetary nebulae, placing particular emphasis on element abundance determinations and comparisons with theoretical predictions. Dust and molecules associated with planetary nebulae are considered as well. We then examine distances, binarity, and planetary nebula morphology and evolution. We end with mention of some of the…
For the upcoming PLAnetary Transits and Oscillation of stars (PLATO) satellite mission, a large number of target stars are required to yield a statistically significant number of planet transits. Locating the centres of the long duration observational phase (LOP) fields closer to the Galactic plane will increase the target star numbers but also the astrophysical false positives (FPs) from blended eclipsing binary systems. We utilise the Binary Stellar Evolution and Population Synthesis (BiSEPS) code, to create a complete synthetic stellar and planetary population for the proposed southern LOP …
Astrophysical objects frequently exhibit some irregularities or complex behaviour in their light curves. We focus primarily on hot stars, where both radial and non-radial pulsations are observed. One of the primary research goals is to determine physical parameters of stellar pulsations by analyzing their light curves or spectra, focusing on periodic or quasiperiodic behaviour. We analyse the feasibility of classical methods for period searches in a nonlinear chaotic system, such as the Rössler system, where a period does not exist at all. As an astrophysical application of the chaotic system,…
It is now clear that a binary pathway is responsible for a significant fraction of planetary nebulae, and the continually increasing sample of known central binaries means that we are now in a position to begin to use these systems to further our understanding of binary evolution. Binary central stars of planetary nebulae are key laboratories in understanding the formation processes of a wide-range of astrophysical phenomena - a point well-illustrated by the fact that the only known double-degenerate, super-Chandrasekhar mass binary which will merge in less than a Hubble time is found inside a…
We report our investigation of the first transiting planet candidate from the YETI project in the young (~4 Myr old) open cluster Trumpler 37. The transit-like signal detected in the lightcurve of the F8V star 2M21385603+5711345 repeats every 1.364894+/-0.000015 days, and has a depth of 54.5+/-0.8 mmag in R. Membership to the cluster is supported by its mean radial velocity and location in the color-magnitude diagram, while the Li diagnostic and proper motion are inconclusive in this regard. Follow-up photometric monitoring and adaptive optics imaging allow us to rule out many possible blend s…
As long as astronomers have searched for exoplanets, the intrinsic variability of host stars has interfered with the ability to reliably detect and confirm exoplanets. One particular source of false positives is the presence of stellar magnetic or chromospheric activity that can mimic the radial-velocity reflex motion of a planet. Here we present the results of a photometric data analysis for the known planet hosting star, BD-06 1339, observed by the Transiting Exoplanet Survey Satellite (TESS) during Sector 6 at 2 minute cadence. We discuss evidence that suggests the observed 3.9 day periodic…
In this work we present a mathematical model for the propagation of the shock waves that occur in graded density profiles. These waves can occur in a wide range of astrophysical events, such as collisions in planetary and stellar atmospheres, common envelope explosions and peculiar type Ia supernovae. The behaviour of the shock wave and its evolution can be modelled using type II self similar solutions. In such solutions the evolution of the shock wave is determined by boundary conditions at the shock front and a singular point in the shocked region. We show how the evolution can be determined…
We present the results of the second year of exoplanet candidate host speckle observations from the SOAR TESS survey. We find 89 of the 589 newly observed TESS planet candidate hosts have companions within 3\arcsec, resulting in light curve dilution, that if not accounted for leads to underestimated planetary radii. We combined these observations with those from paper I to search for evidence of the impact binary stars have on planetary systems. Removing the quarter of the targets observed identified as false-positive planet detections, we find that transiting planet are suppressed by nearly a…
Detecting anions in space has relied on a strong collaboration between theoretical and laboratory analyses to measure rotational spectra and spectroscopic constants to high accuracy. The advent of improved quantum chemical tools operating at higher accuracy and reduced computational cost is a crucial solution for the fundamental characterization of astrophysically-relevant anions and their detection in the interstellar medium and planetary atmospheres. In this context, we have turned towards the quantum chemical analysis of the penta-atomic dicyanoamine anion NCNCN$^-$ (C$_2$N$_3^-$), a struct…
It is now clear that a binary evolutionary pathway is responsible for a significant fraction of all planetary nebulae, with some authors even going so far as to claim that binarity may be a near requirement for the formation of an observable nebula. In this chapter, we will discuss the theoretical and observational support for the importance of binarity in the formation of planetary nebulae, initially focussing on common envelope evolution but also covering wider binaries. Furthermore, we will highlight the impact that these results have on our understanding of other astrophysical phenomena, i…
It is now clear that central star binarity plays a key role in the formation and evolution of planetary nebulae, with a significant fraction playing host to close-binary central stars which have survived one or more common envelope episodes. Recent studies of these systems have revealed many surprises which place important constraints on the common envelope - a critical phase in the formation of a wide variety of astrophysical phenomena, including the cosmologically important supernovae type ia and other transient phenomena which will be detected by next-generation facilities, like the Large S…
A brief review is given of the Rossby wave instability (RWI) in astrophysical discs. In non-self-gravitating discs, around for example a newly forming stars, the instability can be triggered by an axisymmetric bump at some radius $r_0$ in the disc surface mass-density. It gives rise to exponentially growing non-axisymmetric perturbation [$\propto \exp({\rm i}mϕ)$, $m=1,2..$] in the vicinity of $r_0$ consisting of {\it anticyclonic} vortices. These vortices are regions of high pressure and consequently act to trap dust particles which in turn can facilitate planetesimal growth in proto-planetar…
We have analyzed new and previously published radial velocity observations of MARVELS-1, known to have an ostensibly substellar companion in a ~6- day orbit. We find significant (~100 m/s) residuals to the best-fit model for the companion, and these residuals are naively consistent with an interior giant planet with a P = 1.965d in a nearly perfect 3:1 period commensuribility (|Pb/Pc - 3| < 10^{-4}). We have performed several tests for the reality of such a companion, including a dynamical analysis, a search for photometric variability, and a hunt for contaminating stellar spectra. We find man…
As is the case for all techniques involved in the research for exoplanets, direct imaging has to take into account the probability of so-called astrophysical false positives, which are phenomena that mimic the signature of objects we are seeking. In this work we aim to present a case of a false positive found during a direct imaging survey conducted with VLT/NACO. A promising exoplanet candidate was detected around the K2-type star HD\,8049 in July 2010.Its contrast of $ΔH$=7.05 at 1.57 arcsec allowed us to guess the presence of a 35 \MJup companion at 50 projected AU, for the nominal system a…
Planetary nebulae (PNe) represent the near endpoints of evolution for stars of initial mass $\sim$1-8 $M_\odot$, wherein the envelope of an asymptotic giant branch (AGB) star becomes photodissociated and ionized by high-energy radiation from a newly emerging white dwarf that was the progenitor star's core. It is increasingly evident that most PNe are descended from binary systems. PNe hence provide unique insight into a diverse range of astrophysical phenomena, including the influence of companion stars on the late stages of stellar evolution; stellar wind interactions and shocks; the physics …
Using the OSIRIS instrument installed on the 10.4-m Gran Telescopio Canarias (GTC) we acquired multi-color transit photometry of four small (Rp < 5 R_Earth) short-period (P < 6 days) planet candidates recently identified by the Kepler space mission. These observations are part of a program to constrain the false positive rate for small, short-period Kepler planet candidates. Since planetary transits should be largely achromatic when observed at different wavelengths (excluding the small color changes due to stellar limb darkening), we use the observed transit color to identify candidates as ei…
Close binary central stars of planetary nebulae are key in constraining the poorly-understood common-envelope phase of evolution, which in turn is critical in understanding the formation of a wide-range of astrophysical phenomena (including cataclysmic variables, low-mass X-ray binaries and supernovae type Ia). Here, I present the results of our on-going, targeted search for close-binaries in planetary nebulae which has led to the discovery of more than 10 new central binaries in just the last few years (almost the same as the total discovered during the 1980s and 1990s together). This success…
The late-type dwarf GJ 436 is known to host a transiting Neptune-mass planet in a 2.6-day orbit. We present results of our interferometric measurements to directly determine the stellar diameter ($R_{\star} = 0.455 \pm 0.018 R_{\odot}$) and effective temperature ($T_{\rm EFF} = 3416 \pm 54$ K). We combine our stellar parameters with literature time-series data, which allows us to calculate physical and orbital system parameters, including GJ 436's stellar mass ($M_{\star} = 0.507^{+ 0.071}_{- 0.062} M_{\odot}$) and density ($ρ_* = 5.37^{+ 0.30}_{- 0.27} ρ_\odot$), planetary radius ($R_{p} = 0.…
We present a framework to conservatively estimate the probability that any particular planet-like transit signal observed by the Kepler mission is in fact a planet, prior to any ground-based follow-up efforts. We use Monte Carlo methods based on stellar population synthesis and Galactic structure models, and report a priori false positive probabilities for every Kepler Object of Interest in tabular form, assuming a 20% intrinsic occurrence rate of close-in planets in the radius range 0.5 Rearth < Rp < 20 Rearth. Almost every candidate has FPP <10%, and over half have FPP <5%. This probability …
(abridged) Observations of exoplanets indicate the existence of several correlations in the architecture of planetary systems. Exoplanets within a system tend to be of similar size and mass, evenly spaced, and are often ordered in size and mass. Small planets are frequently packed in tight configurations, while large planets often have wider orbital spacing. Together, these correlations are called the peas in a pod trends in the architecture of planetary systems. In this paper these trends are investigated in theoretically simulated planetary systems and compared with observations. Whether the…
The stellar initial mass function (IMF) is a fundamental astrophysical quantity that impacts a wide range of astrophysical problems from heavy element distribution to galactic evolution to planetary system formation. However, the origin and universality of the IMF are hotly debated both observationally and theoretically. I review recent observations of the IMF across a variety of environments. These suggest the IMF is surprisingly invariant between star-forming regions, star clusters, and spiral galaxies but that it may also vary under extreme conditions, including within the Galactic center a…
The common-envelope phase is one of the most poorly understood phases of (binary) stellar evolution, in spite of its importance in the formation of a wide-range of astrophysical phenomena ranging from cataclysmic variables to cosmologically important supernova type Ia, and even recently discovered gravitational wave producing black hole mergers. The central star of the planetary nebula NGC~2346 has long been held as one of the longest period post-common-envelope systems known with a published period of approximately 16 days, however the data presented were also consistent with much shorter per…
The extended Kepler mission, K2, is now providing photometry of new fields every three months in a search for transiting planets. In a recent study, Foreman-Mackey and collaborators presented a list of 36 planet candidates orbiting 31 stars in K2 Campaign 1. In this contribution, we present stellar and planetary properties for all systems. We combine ground-based seeing-limited survey data and adaptive optics imaging with an automated transit analysis scheme to validate 21 candidates as planets, 17 for the first time, and identify 6 candidates as likely false positives. Of particular interest …
We recently used near-infrared spectroscopy to improve the characterization of 76 low-mass stars around which K2 had detected 79 candidate transiting planets. Thirty of these worlds were new discoveries that have not previously been published. We calculate the false positive probabilities that the transit-like signals are actually caused by non-planetary astrophysical phenomena and reject five new transit-like events and three previously reported events as false positives. We also statistically validate 18 planets (eight of which were previously unpublished), confirm the earlier validation of …
Barnard's star is among the most studied stars given its proximity to the Sun. It is often considered $the$ Radial Velocity (RV) standard for fully convective stars due to its RV stability and equatorial declination. Recently, an $M \sin i = 3.3 M_{\oplus}$ super-Earth planet candidate with a 233 day orbital period was announced by Ribas et al. (2018). New observations from the near-infrared Habitable-zone Planet Finder (HPF) Doppler spectrometer do not show this planetary signal. We ran a suite of experiments on both the original data and a combined original + HPF data set. These experiments …
We analyzed the photometry of 20038 cool stars from campaigns 12, 13, 14 and 15 of the K2 mission in order to detect, characterize and validate new planetary candidates transiting low-mass stars. We present a catalogue of 25 new periodic transit-like signals in 22 stars, of which we computed the parameters of the stellar host for 19 stars and the planetary parameters for 21 signals. We acquired speckle and AO images, and also inspected archival Pan-STARRS1 images and Gaia DR2 to discard the presence of close stellar companions and to check possible transit dilutions due to nearby stars. False …
Context. The CoRoT satellite searches for planets by applying the transit method, monitoring up to 12 000 stars in the galactic plane for 150 days in each observation run. This search is contaminated by a large fraction of false positives, caused by different binary configurations that might be confused with a transiting planet. Aims. We evaluate the rates and nature of false positives in the CoRoT exoplanets search and compare our results with semiempirical predictions. Methods. We consider the detected binary and planet candidates in the first three extended CoRoT runs, and classify the resu…
The bright star 55 Cancri is known to host five planets, including a transiting super-Earth. The study presented here yields directly determined values for 55 Cnc's stellar astrophysical parameters based on improved interferometry: $R=0.943 \pm 0.010 R_{\odot}$, $T_{\rm EFF} = 5196 \pm 24$ K. We use isochrone fitting to determine 55 Cnc's age to be 10.2 $\pm$ 2.5 Gyr, implying a stellar mass of $0.905 \pm 0.015 M_{\odot}$. Our analysis of the location and extent of the system's habitable zone (0.67--1.32 AU) shows that planet f, with period $\sim$ 260 days and $M \sin i = 0.155 M_{Jupiter}$, s…
The Chandra X-ray Observatory has completed a remarkable twenty years in orbit. A large part of the science program of Chandra during this time has involved the study of stars and their planetary systems. This primer aims to give the reader a taste of the enormous range of stellar and planetary astrophysics that Chandra has enabled. Beginning with a tour of the X-ray solar system zoo, including the stunning pulsating X-ray aurorae of Jupiter, we then move on to the hot million-degree outer atmospheres of stars like our own Sun, whose X-ray emission is driven by an internal magnetic dynamo. The…
Kepler Mission's single-band photometry suffers from astrophysical false positives, the most common of background eclipsing binaries (BEBs) and companion transiting planets (CTPs). Multi-color photometry can reveal the color-dependent depth feature of false positives and thus exclude them. In this work, we aim to estimate the fraction of false positives that are unable to be classified by Kepler alone but can be identified with their color-dependent depth feature if a reference band (z, Ks and TESS) were adopted in follow-up observation. We build up physics-based blend models to simulate multi…
Two Potential Exoplanets around A-type Stars Selected from 18 Planetary Candidates
Yunnan Observatories, Chinese Academy of Sciences (CAS)（中国科学院云南天文台）；University of Chinese Academy of Sciences（中国科学院大学）；School of Physics and Astronomy, Yunnan University（云南大学物理与天文学院）
We present line lists for ammonia (NH$_{3}$) at high temperatures obtained by recording Fourier transform infrared emission spectra. Calibrated line lists are presented for twelve temperatures (300 -- 1300$^{\circ}$C in 100$^{\circ}$C intervals and 1370$^{\circ}$C) and each line list covers the 740 -- 2100 cm$^{-1}$ range, which includes the majority of the $ν_{2}$ umbrella bending mode region (11 $μ$m) and the $ν_{4}$ asymmetric bending mode region (6.2 $μ$m). We also demonstrate the useful technique of obtaining empirical lower state energies from a set of spectra recorded at different sampl…
