We report the discovery of the closest known black hole candidate as a binary companion to V723 Mon. V723 Mon is a nearby (d=460 pc), bright evolved red giant in a high mass function nearly circular binary (𝑃 = 59.9 d, e approx. 0). Analyses of the stellar spectra and spectral energy distribution (SED) give 𝑇eff = 4440 K, 𝐿 = 173 𝐿s⊙ and 𝑅 = 22 𝑅⊙. Matching these parameters to MIST evolutionary models indicates a mass of the visible giant of 𝑀giant = 1.07 +/- 0.24 𝑀⊙. V723 Mon is a known variable star, previously classified as an eclipsing binary, but its All-Sky Automated Survey (ASAS), Kilodegree Extremely Little Telescope (KELT), and Transiting Exoplanet Survey Satellite (TESS) light curves are those of a nearly edge-on ellipsoidal variable. Detailed models of the light curves constrained by the period, radial velocities and stellar temperature give an inclination of 𝑖 = 87 deg, a mass ratio of 0.30 +/- 0.02, and a companion mass of 𝑀comp = 2.91 +/- 0.08 𝑀⊙, a stellar radius of the giant of 𝑅giant = 23.6 +/-1.0 𝑅⊙, and a giant mass of 𝑀giant = 0.87 +/-0.08 𝑀⊙ , consistent with our other estimates. We identify a likely non-stellar, diffuse veiling component with contributions in the 𝐵 and 𝑉-band of ~64% and ~23%, respectively, and a luminosity of ~20 𝐿⊙. The SED and the absence of continuum eclipses imply that the companion mass must be dominated by a compact object even if the companion is a binary. We do observe eclipses of the Balmer lines when the dark companion passes behind the giant, but their velocity spreads are low compared to observed accretion disks. The X-ray luminosity of the system is 𝐿X = 1 x 10^30 erg/s, corresponding to 𝐿/𝐿edd ~10^-9. The simplest explanation for the massive companion is a single compact object, most likely a black hole in the “mass gap”, although a double neutron star binary is possible.
NGC 1624-2 is an O7f?p star with a reported probable polar magnetic field strength ≥20 kG, which is the strongest magnetic field ever measured in an O-type star. We study the variability of the mean longitudinal magnetic field <Bz> and the mean field modulus to obtain constraints on its field geometry. Only one magnetic pole is observable over the rotation cycle. The approximately sinusoidal variation of <Bz> and the ratio of the values of the extrema of indicate that there is an important component of the field that is dipolar. The <Bz> values measured over the rotation cycle are in the range from -0.2 to 4.5 kG, whereas the values for vary between 9 and 12 kG. The <Bz> values obtained using the O III λ7455 emission line are in the range from 0.4 to 2.3 kG and show a variability pattern similar to that detected for the absorption lines. The fact that the phase of the <Bz> minimum coincides with the phase of the maximum, indicates that the field structure must significantly depart from a centred dipole. Further, we discuss the nature of the observed variable Stokes V profiles corresponding to a longitudinal field of negative polarity detected in the emission He I lines and present the first magnetohydrodynamical numerical simulations of the gas flow in the magnetosphere of this star.
A long sought after goal using chemical abundance patterns derived from metal-poor stars is to understand the chemical evolution of the Galaxy and to pin down the nature of the first stars (Pop III). Metal-poor, old, unevolved stars are excellent tracers as they preserve the abundance pattern of the gas from which they were born, and hence they are frequently targeted in chemical tagging studies. Here, we use a sample of 14 metal-poor stars observed with the high-resolution spectrograph called the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) to derive abundances of 32 elements (34 including upper limits). We present well-sampled abundance patterns for all stars obtained using local thermodynamic equilibrium (LTE) radiative transfer codes and one-dimensional (1D) hydrostatic model atmospheres. However, it is currently well-known that the assumptions of 1D and LTE may hide several issues, thereby introducing biases in our interpretation as to the nature of the first stars and the chemical evolution of the Galaxy. Hence, we use non-LTE (NLTE) and correct the abundances using three-dimensional (3D) model atmospheres to present a physically more reliable pattern. In order to infer the nature of the first stars, we compare unevolved, cool stars, which have been enriched by a single event (‘mono-enriched’), with a set of yield predictions to pin down the mass and energy of the Pop III progenitor. To date, only few bona fide second generation stars that are mono-enriched are known. A simple χ 2 -fit may bias our inferred mass and energy just as much as the simple 1D LTE abundance pattern, and we therefore carried out our study with an improved fitting technique considering dilution and mixing. Our sample presents Carbon Enhanced Metal-Poor (CEMP) stars, some of which are promising bona fide second generation (mono-enriched) stars. The unevolved, dwarf BD+09_2190 shows a mono-enriched signature which, combined with kinematical data, indicates that it moves in the outer halo and likely has been accreted onto the Milky Way early on. The Pop III progenitor was likely of 25.5 M and 0.6 foe (0.6 1051 erg) in LTE and 19.2 M and 1.5 foe in NLTE, respectively. Finally, we explore the predominant donor and formation site of the rapid and slow neutron-capture elements.
Comparing chemical abundances of a planet and the host star reveals the origin and formation pathway of the planet. Stellar abundance is measured with high-resolution spectroscopy. Planet abundance, on the other hand, is usually inferred from low-resolution data. For directly imaged exoplanets, the data are available from a slew of high-contrast imaging/spectroscopy instruments. Here, we study the chemical abundance of HR 8799 and its planet c. We measure stellar abundance using LBT/PEPSI (R=120,000) and archival HARPS data: stellar [C/H], [O/H], and C/O are 0.11±0.12, 0.12±0.14, and 0.54+0.09-0.12, all consistent with solar values. We conduct atmospheric retrieval using newly obtained Subaru/CHARIS data together with archival Gemini/GPI and Keck/OSIRIS data. We model the planet spectrum with petitRADTRANS and conduct retrieval using PyMultiNest. Retrieved planetary abundance can vary by ∼0.5 dex, from sub-stellar to stellar C and O abundances. The variation depends on whether strong priors are chosen to ensure a reasonable planet mass. Moreover, comparison with previous works also reveals inconsistency in abundance measurements. We discuss potential issues that can cause the inconsistency, e.g., systematics in individual data sets and different assumptions in the physics and chemistry in retrieval. We conclude that no robust retrieval can be obtained unless the issues are fully resolved.
Gaia benchmark stars are selected to be calibration stars for different spectroscopic surveys. Very high-quality and homogeneous spectroscopic data for these stars are therefore required. We collected ultrahigh-resolution ESPRESSO spectra for 30 of the 34 Gaia benchmark stars and made them public. We quantify the consistency of the results that are obtained with different high-, and ultrahigh-resolution spectrographs. We also comprehensively studied the effect of using different spectral reduction products of ESPRESSO on the final spectroscopic results. We used ultrahigh- and high-resolution spectra obtained with the ESPRESSO, PEPSI, and HARPS spectrographs to measure spectral line characteristics (line depth; line width; and EW) and determined stellar parameters and abundances for a subset of 11 Gaia benchmark stars. The EW spectral line measurements based on the ESPRESSO, PEPSI, and HARPS spectra agree to within a few percent. However, we note that the lines appear deeper in the ESPRESSO spectra than in PEPSI and HARPS. The stellar parameters derived from each spectrograph by combining the several available spectra agree well overall. We conclude that the ESPRESSO, PEPSI, and HARPS spectrographs can deliver spectroscopic results that are sufficiently consistent for most of the science cases in stellar spectroscopy.
A team around Engin Keles (AIP) compared previously observed high resolution Na I and K I absorption in the atmosphere of HD189733b with synthetic transmission spectra modeled for a variety of temperature and abundance values. The comparison showed that the observed Na I-D-line widths are much larger than the modeled ones. The Na I-D-lines had to be broadened by velocities in the order of 10 km/s to match the observations if only rotational broadening is taken into account. The K I line profile on the other hand showed only a few km/s broadening comparable with the synthetic line profiles. This hints that either the atmosphere of HD 189733b lacks a significant amount of K I or the alkali lines probe different atmospheric regions with different temperature, which could explain the differences in the resolved absorption lines.
T Coronae Borealis is a recurrent, symbiotic nova system currently in quiescence between its periodic ≍80 yr cycle of eruptions. Observations during inter-outburst epochs provide an opportunity to study properties of the accretion disk and the M red giant. Here we present new irradiated (blackbody veiling) models, incorporating modern molecular opacities and line lists, of spectra derived from high-resolution (22,000 ≲ R ≲ 120,000) optical echelle observations obtained at two epochs, one prior to and one post the 2015 rebrightening event at similar spectroscopic system phase. We find a lithium abundance in the secondary at both epochs to be comparable. The non-irradiated (classical) model atmospheres yield a lithium abundance, A(Li) = 1.3 ± 0.1. The irradiated model (veiled) atmospheres, which are likely a better representation of the system in which the white dwarf and accretion disk illuminate the red giant, give A(Li) = 2.4 ± 0.1.
We observed a partial transit of the ultra-hot Jupiter WASP-189 b with PEPSI on the LBT. We detect a highly variable transit signal in multiple atomic transitions, including H-alpha, Fe I, and Mg I. The signal is not consistent with a transiting planetary atmosphere. We suggest instead that the in-transit signal is due to an inhomogeneous stellar surface. Our observations demonstrate the lack of a highly extended atmosphere in common optical atomic tracers. Although WASP-189 is very bright, atmospheric characterization of the planet will be difficult due to the small transit depth and apparently compact atmosphere.
January 2019 featured a total lunar eclipse. The Moon dimmed by a factor of 20,000 (10.75 mag) during totality. Therefore, the light gathering capability of the 11.8 m Large Binocular Telescope (LBT) in Arizona was needed for the observations. Additionally, the high spectral resolution of the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) was necessary to separate the expected tiny spectral-line absorptions of the Earth’s atmosphere from the normal solar spectrum at unprecedented spectral resolution and in polarized light. The radial velocities trace a wavelength dependent Rossiter-McLaughlin effect of the Earth eclipsing the Sun as seen from the Tycho crater confirming earlier observations. No line polarization of any spectral-line feature is detected outside nor inside eclipse. This places an upper limit of ≈0.2% on the degree of line polarization during transmission through Earth’s atmosphere and magnetosphere.
Synoptic Sun-as-a-star observations are carried out with the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI), which receives light from the Solar Disk-Integration (SDI) telescope. Daily spectra are produced with a high signal-to-noise ratio, providing access to unprecedented quasi-continuous, long-term, disk-integrated spectra of the Sun with high spectral and temporal resolution. We developed tools to monitor and study solar activity on different time-scales ranging from daily changes, over periods related to solar rotation, to annual and decadal trends. Strong chromospheric absorption lines, such as the Ca II H & K λ3934 & 3968 Å lines, are powerful diagnostic tools for solar activity studies, since they trace the variations of the solar magnetic field. Other lines, such as Hα λ6563 Å line and the near-infrared (NIR) Ca II λ8542 Å line, provide additional information on the physical properties in this highly complex and dynamic atmospheric layer. Currently, we work on a data pipeline for extraction, calibration, and analysis of the PEPSI/SDI data. We compare the SDI data with daily spectra from the Integrated Sunlight Spectrometer (ISS), which is part of the Synoptic Long-Term Investigation of the Sun (SOLIS) facility operated by the U.S. National Solar Observatory (NSO). This facilitates cross-calibration and validation of the SDI data.