State-of-the-art radial-velocity (RV) exoplanet searches are currently limited by RV signals arising from stellar magnetic activity. We analyze solar observations acquired over a 3 yr period during ...the decline of Carrington Cycle 24 to test models of RV variation of Sun-like stars. A purpose-built solar telescope at the High Accuracy Radial-velocity Planet Searcher for the Northern hemisphere (HARPS-N) provides disk-integrated solar spectra, from which we extract RVs and log R HK ′ . The Solar Dynamics Observatory (SDO) provides disk-resolved images of magnetic activity. The Solar Radiation and Climate Experiment (SORCE) provides near-continuous solar photometry, analogous to a Kepler light curve. We verify that the SORCE photometry and HARPS-N log R HK ′ correlate strongly with the SDO-derived magnetic filling factor, while the HARPS-N RV variations do not. To explain this discrepancy, we test existing models of RV variations. We estimate the contributions of the suppression of convective blueshift and the rotational imbalance due to brightness inhomogeneities to the observed HARPS-N RVs. We investigate the time variation of these contributions over several rotation periods, and how these contributions depend on the area of active regions. We find that magnetic active regions smaller than 60 Mm2 do not significantly suppress convective blueshift. Our area-dependent model reduces the amplitude of activity-induced RV variations by a factor of two. The present study highlights the need to identify a proxy that correlates specifically with large, bright magnetic regions on the surfaces of exoplanet-hosting stars.
The early afterglow of GRB 190829A Dichiara, S; Troja, E; Lipunov, V ...
Monthly notices of the Royal Astronomical Society,
03/2022, Letnik:
512, Številka:
2
Journal Article
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ABSTRACT
GRB 190829A at z = 0.0785 is the fourth closest long GRB ever detected by the Neil Gehrels Swift observatory, and the third confirmed case with a very high-energy component. We present our ...multiwavelength analysis of this rare event, focusing on its early stages of evolution, and including data from Swift, the MASTER global network of optical telescopes, ALMA, and ATCA. We report sensitive limits on the linear polarization of the optical emission, disfavouring models of off-axis jets to explain the delayed afterglow peak. The study of the multiwavelength light curves and broad-band spectra supports a model with at least two emission components: a bright reverse shock emission, visible at early times in the optical and X-rays and, later, in the radio band; and a forward shock component dominating at later times and lower radio frequencies. A combined study of the prompt and afterglow properties shows many similarities with cosmological long GRBs, suggesting that GRB 190829A is an example of classical GRBs in the nearby universe.
Context.
The solar telescope connected to HARPS-N has been observing the Sun since the summer of 2015. Such a high-cadence, long-baseline data set is crucial for understanding spurious ...radial-velocity signals induced by our Sun and by the instrument. On the instrumental side, this data set allowed us to detect sub- m s
−1
systematics that needed to be corrected for.
Aims.
The goals of this manuscript are to (i) present a new data reduction software for HARPS-N, (ii) demonstrate the improvement brought by this new software during the first three years of the HARPS-N solar data set, and (iii) release all the obtained solar products, from extracted spectra to precise radial velocities.
Methods.
To correct for the instrumental systematics observed in the data reduced with the current version of the HARPS-N data reduction software (DRS version 3.7), we adapted the newly available ESPRESSO DRS (version 2.2.3) to HARPS-N and developed new optimised recipes for the spectrograph. We then compared the first three years of HARPS-N solar data reduced with the current and new DRS.
Results.
The most significant improvement brought by the new DRS is a strong decrease in the day-to-day radial-velocity scatter, from 1.27 to 1.07 m s
−1
; this is thanks to a more robust method to derive wavelength solutions, but also to the use of calibrations closer in time. The newly derived solar radial-velocities are also better correlated with the chromospheric activity level of the Sun in the long term, with a Pearson correlation coefficient of 0.93 compared to 0.77 before, which is expected from our understanding of stellar signals. Finally, we also discuss how HARPS-N spectral ghosts contaminate the measurement of the calcium activity index, and we present an efficient technique to derive an index free of instrumental systematics.
Conclusions.
This paper presents a new data reduction software for HARPS-N and demonstrates its improvements, mainly in terms of radial-velocity precision, when applied to the first three years of the HARPS-N solar data set. Those newly reduced solar data, representing an unprecedented time series of 34 550 high-resolution spectra and precise radial velocities, are released alongside this paper. Those data are crucial to understand stellar activity signals in solar-type stars further and develop the mitigating techniques that will allow us to detect other Earths.
Abstract
The time-variable velocity fields of solar-type stars limit the precision of radial-velocity determinations of their planets’ masses, obstructing detection of Earth twins. Since 2015 July, ...we have been monitoring disc-integrated sunlight in daytime using a purpose-built solar telescope and fibre feed to the HARPS-N stellar radial-velocity spectrometer. We present and analyse the solar radial-velocity measurements and cross-correlation function (CCF) parameters obtained in the first 3 yr of observation, interpreting them in the context of spatially resolved solar observations. We describe a Bayesian mixture-model approach to automated data-quality monitoring. We provide dynamical and daily differential-extinction corrections to place the radial velocities in the heliocentric reference frame, and the CCF shape parameters in the sidereal frame. We achieve a photon-noise-limited radial-velocity precision better than 0.43 m s−1 per 5-min observation. The day-to-day precision is limited by zero-point calibration uncertainty with an RMS scatter of about 0.4 m s−1. We find significant signals from granulation and solar activity. Within a day, granulation noise dominates, with an amplitude of about 0.4 m s−1 and an autocorrelation half-life of 15 min. On longer time-scales, activity dominates. Sunspot groups broaden the CCF as they cross the solar disc. Facular regions temporarily reduce the intrinsic asymmetry of the CCF. The radial-velocity increase that accompanies an active-region passage has a typical amplitude of 5 m s−1 and is correlated with the line asymmetry, but leads it by 3 d. Spectral line-shape variability thus shows promise as a proxy for recovering the true radial velocity.
ABSTRACT
To push the radial velocity (RV) exoplanet detection threshold, it is crucial to find more reliable RV extraction methods. The least-squares deconvolution (LSD) technique has been used to ...infer the stellar magnetic flux from spectropolarimetric data for the past two decades. It relies on the assumption that stellar absorption lines are similar in shape. Although this assumption is simplistic, LSD provides a good model for intensity spectra and likewise an estimate for their Doppler shift. We present the multi-mask least-squares deconvolution (MM-LSD) RV extraction pipeline that extracts the RV from two-dimensional echelle-order spectra using LSD with multiple tailored masks after continuum normalization and telluric absorption line correction. The flexibility of LSD allows to exclude spectral lines or pixels at will, providing a means to exclude variable lines or pixels affected by instrumental problems. The MM-LSD pipeline was tested on HARPS-N data for the Sun and selected well-observed stars with 5.7 < Vmag < 12.6. For FGK-type stars with median signal-to-noise ratio above 100, the pipeline delivered RV time series with on average 12 per cent lower scatter as compared to the HARPS-N RV extraction pipeline based on the cross-correlation function technique. The MM-LSD pipeline may be used as a standalone RV code, or modified and extended to extract a proxy for the magnetic field strength.
ABSTRACT
Magnetic chemically peculiar stars of the main sequence can present rotational periods as long as many decades. Here we report the results of an observational campaign started in 2001 aimed ...at establishing these very long periods from the variability of the integrated magnetic field modulus, the so-called surface magnetic field Bs, as measured from the Zeeman splitting of the Fe ii 6149.258 Å spectral line. 36 stars have been monitored with various high-resolution spectrographs at different telescopes, totalling 412 newly collected spectra. To improve the phase coverage, we have also exploited all public archives containing high-resolution spectra, many not yet published. On the basis of these new Bs variability curves, we (1) confirm or revisit the periods of 24 stars, (2) extend the lower limits to the periods of HD 55719 (P > 38 yr), HD 165474 (P > 27 yr), and HD 177765 (P > 37 yr), (3) establish for the first time the periods of HD 29578 (P = 10.95 yr), HD 47103 (P = 17.683 d), HD 150562 (P = 5.7 yr), and HD 216018 (P = 34.044 d), and (4) set lower limits to the periods of HD 75445 (P »14 yr), HD 110066 (P » 29 yr), HD 116114 (P > 48 yr), and HD 137949 (P > 27 yr). As to γ Equ, whose period must exceed 90 yr, we point out a clear decrease in the field modulus, the maximum of which coincides within the uncertainties with the minimum of the variation in the integrated longitudinal field.
Abstract Background There are limited data comparing ultrafiltration with standard medical therapy as first-line treatment in patients with severe congestive heart failure (HF). We compared ...ultrafiltration and conventional therapy in patients hospitalized for HF and overt fluid overload. Methods and Results Fifty-six patients with congestive HF were randomized to receive standard medical therapy (control group; n = 29) or ultrafiltration (ultrafiltration group; n = 27). The primary end point of the study was rehospitalizations for congestive HF during a 1-year follow-up. Despite similar body weight reduction at hospital discharge in the 2 groups (7.5 ± 5.5 and 7.9 ± 9.0 kg, respectively; P = .75), a lower incidence of rehospitalizations for HF was observed in the ultrafiltration-treated patients during the following year (hazard ratio 0.14, 95% confidence interval 0.04–0.48; P = .002). Ultrafiltration-induced benefit was associated with a more stable renal function, unchanged furosemide dose, and lower B-type natriuretic peptide levels. At 1 year, 7 deaths (30%) occurred in the ultrafiltration group and 11 (44%) in the control group ( P = .33). Conclusions In HF patients with severe fluid overload, first-line treatment with ultrafiltration is associated with a prolonged clinical stabilization and a greater freedom from rehospitalization for congestive HF.
In an attempt to understand the findings presented in the Comment by Greaves et al. (2023, https://doi.org/10.1029/2023GL103539), we followed their data analysis methodology, omitting the hot and ...cold‐load calibrations that are an important part of the standard SOFIA GREAT instrument calibration procedure. This process requires scaling of the Venus off‐source spectra by an arbitrary factor, which in turn introduces residuals of the intrinsic receiver bandpass shape as spurious components in the resulting line/continuum spectra. Although these additional artifacts can be reduced via Fourier‐domain spectral filtering, their removal depends on an ill‐constrained interpolation of the Venus continuum across the PH3 spectral line positions, resulting in an unreliable final spectrum. We therefore conclude that the PH3 lines claimed to be detected in the Comment by Greaves et al. (2023, https://doi.org/10.1029/2023GL103539) originate from data/analysis artifacts, and confirm our original result that there is no evidence for phosphine in the SOFIA Venus data.
Plain Language Summary
We performed observations using a unique, flying telescope—the Stratospheric Observatory for Infrared Astronomy (SOFIA)—to search for a gas called phosphine in the atmosphere of Venus, which has been suggested to be an indicator for life. The observations, published by Cordiner et al. (2022, https://doi.org/10.1029/2022gl101055), were analyzed carefully but showed no evidence of phosphine. Our findings were called into question in the Comment by Greaves et al. (2023, https://doi.org/10.1029/2023GL103539), who claimed to find phosphine lines in the SOFIA observations after following an unconventional data analysis method. We have investigated their method, and conclude that it is likely to introduce spurious signals into the data, so the claimed phosphine detection is therefore not significant.
Key Points
The revised calibration procedure adopted by Greaves et al. (2023, https://doi.org/10.1029/2023GL103539) introduces additional receiver artifacts into the SOFIA 4G2 Venus spectra
The claimed PH3 detection is likely a result of this, combined with interpolation artifacts that occur during subsequent Fourier filtering
We confirm our original conclusion that there is no evidence for phosphine in the SOFIA GREAT Venus data
ABSTRACT
Stellar magnetic activity produces time-varying distortions in the photospheric line profiles of solar-type stars. These lead to systematic errors in high-precision radial-velocity ...measurements, which limit efforts to discover and measure the masses of low-mass exoplanets with orbital periods of more than a few tens of days. We present a new data-driven method for separating Doppler shifts of dynamical origin from apparent velocity variations arising from variability-induced changes in the stellar spectrum. We show that the autocorrelation function (ACF) of the cross-correlation function used to measure radial velocities is effectively invariant to translation. By projecting the radial velocities on to a subspace labelled by the observation identifiers and spanned by the amplitude coefficients of the ACF’s principal components, we can isolate and subtract velocity perturbations caused by stellar magnetic activity. We test the method on a 5-yr time sequence of 853 daily 15-min observations of the solar spectrum from the HARPS-N instrument and solar-telescope feed on the 3.58-m Telescopio Nazionale Galileo. After removal of the activity signals, the heliocentric solar velocity residuals are found to be Gaussian and nearly uncorrelated. We inject synthetic low-mass planet signals with amplitude K = 40 cm s−1 into the solar observations at a wide range of orbital periods. Projection into the orthogonal complement of the ACF subspace isolates these signals effectively from solar activity signals. Their semi-amplitudes are recovered with a precision of ∼ 6.6 cm s−1, opening the door to Doppler detection and characterization of terrestrial-mass planets around well-observed, bright main-sequence stars across a wide range of orbital periods.
ABSTRACT
Based on HARPS-N radial velocities (RVs) and TESS photometry, we present a full characterization of the planetary system orbiting the late G dwarf TOI-561. After the identification of three ...transiting candidates by TESS, we discovered two additional external planets from RV analysis. RVs cannot confirm the outer TESS transiting candidate, which would also make the system dynamically unstable. We demonstrate that the two transits initially associated with this candidate are instead due to single transits of the two planets discovered using RVs. The four planets orbiting TOI-561 include an ultra-short period (USP) super-Earth (TOI-561 b) with period Pb = 0.45 d, mass Mb = 1.59 ± 0.36 M⊕ and radius Rb = 1.42 ± 0.07 R⊕, and three mini-Neptunes: TOI-561 c, with Pc = 10.78 d, Mc = 5.40 ± 0.98 M⊕, Rc = 2.88 ± 0.09 R⊕; TOI-561 d, with Pd = 25.6 d, Md = 11.9 ± 1.3 M⊕, Rd = 2.53 ± 0.13 R⊕; and TOI-561 e, with Pe = 77.2 d, Me = 16.0 ± 2.3 M⊕, Re = 2.67 ± 0.11 R⊕. Having a density of 3.0 ± 0.8 g cm−3, TOI-561 b is the lowest density USP planet known to date. Our N-body simulations confirm the stability of the system and predict a strong, anti-correlated, long-term transit time variation signal between planets d and e. The unusual density of the inner super-Earth and the dynamical interactions between the outer planets make TOI-561 an interesting follow-up target.
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