Joshua T Briegal; Edward Gillen; D. Queloz; S. T. Hodgkin; Jack S Acton; D. R. Anderson; D. J. Armstrong; Matthew P. Battley; Daniel Bayliss; M. R. Burleigh; Edward M. Bryant; S. L. Casewell; Jean C Costes; Philipp Eigmüller; Samuel Gill; M. R. Goad; Maximilian N. Günther; Beth A Henderson; James A. G. Jackman; J. S. Jenkins; Lars T. Kreutzer; Maximiliano Moyano; M. Lendl; Gareth Smith; Rosanna H Tilbrook; C. A. Watson; R. G. West; P. J. Wheatley
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT We analyse 829 481 stars from the Next Generation Transit Survey (NGTS) to extract variability periods. We utilize a generalization of the autocorrelation function (the G-ACF), which applies to irregularly sampled time series data. We extract variability periods for 16 880 stars from late-A through to mid-M spectral types and periods between ∼0.1 and 130 d with no assumed variability model. We find variable signals associated with a number of astrophysical phenomena, including stellar rotation, pulsations, and multiple-star systems. The extracted variability periods are compared with stellar parameters taken from Gaia DR2, which allows us to identify distinct regions of variability in the Hertzsprung–Russell Diagram. We explore a sample of rotational main-sequence objects in period-colour space, in which we observe a dearth of rotation periods between 15 and 25 d. This ‘bi-modality’ was previously only seen in space-based data. We demonstrate that stars in sub-samples above and below the period gap appear to arise from a stellar population not significantly contaminated by excess multiple systems. We also observe a small population of long-period variable M-dwarfs, which highlight a departure from the predictions made by rotational evolution models fitted to solar-type main-sequence objects. The NGTS data spans a period and spectral type range that links previous rotation studies such as those using data from Kepler, K2, and MEarth.
L. Galluccio; Marco Delbò; F. De Angeli; Thierry Pauwells; P. Tanga; François Mignard; A. Cellino; Anthony G.A. Brown; K. Muinonen; Antti Penttilä
<p><strong>Abstract</strong></p> <p>The Gaia mission of the European Space Agency (ESA) published its third release (DR3) on June 13, 2022, including for the first time a survey of 60 518 mean reflectance spectra of Solar System objects (SSOs). Each reflectance spectrum was derived from calibrated measurements obtained by the onboard Blue and Red low-resolution spectro-photometers (BP/RP) and consists of sixteen discrete wavelength bands, along with additional information about the data quality for each band.</p> <p>We will describe the processing of the Gaia spectral data of SSOs and the steps of our internal validation procedures. We present the adopted approach for external validation against SSO reflectance spectra available in the literature, obtained from ground-based and space-borne telescopes, to assess the quality of Gaia SSO reflectance spectra. This work summarizes a more detailed description by Galluccio et al. (2022) [1].</p> <ul> <li><strong>Introduction</strong></li> </ul> <p>Gaia DR3 contains information for a sample of more than 150,000 SSOs, including astrometry, photometry, osculating elements, and mean reflectance spectra [2]. The selection of these objects is described by Tanga et al. (2022) [2]. Based on the quality of the data and some criteria developed hereafter, DR3 contains 60518 mean reflectance spectra of Near-Earth Asteroids (NEAs), main-belt asteroids, Jupiter Trojans, transneptunian objects (TNOs), and other classes (Table 1) observed at relatively large phase angles (~20°).</p> <p>Table 1: No. of SSOs with Gaia DR3 spectra for each of the dynamical classes listed on the NASA JPL website. The classes are defined according to the criteria based on the orbital semi-major axis a, the perihelion distance q, and the aphelion distance Q.</p> <table> <tbody> <tr> <td> <p>Dynamical Class</p> </td> <td> <p>No. of SSO</p> </td> <td> <p>Criterion (values in au)</p> </td> </tr> <tr> <td> <p>NEA Aten</p> </td> <td> <p>6</p> </td> <td> <p>a < 1.0 & Q > 0.983</p> </td> </tr> <tr> <td> <p>NEA Apollo</p> </td> <td> <p>52</p> </td> <td> <p>a > 1.0 & q < 1.017</p> </td> </tr> <tr> <td> <p>NEA Amor</p> </td> <td> <p>47</p> </td> <td> <p>1.017 < q < 1.3</p> </td> </tr> <tr> <td> <p>Mars-Crosser</p> </td> <td> <p>729</p> </td> <td> <p>1.3 < q < 1.666</p> </td> </tr> <tr> <td> <p>Inner Main Belt</p> </td> <td> <p>1 221</p> </td> <td> <p>a < 2.0 & q > 1.666</p> </td> </tr> <tr> <td> <p>Main Belt</p> </td> <td> <p>55 976</p> </td> <td> <p>2.0 < a < 3.2 & q > 1.666</p> </td> </tr> <tr> <td> <p>Outer Main Belt</p> </td> <td> <p>1 995</p> </td> <td> <p>3.2 < a < 4.6</p> </td> </tr> <tr> <td> <p>Jupiter Trojan</p> </td> <td> <p>477</p> </td> <td> <p>4.6 < a < 5.5</p> </td> </tr> <tr> <td> <p>Centaur</p> </td> <td> <p>5</p> </td> <td> <p>4.6 < a < 5.5</p> </td> </tr> <tr> <td> <p>TNO</p> </td> <td> <p>7</p> </td> <td> <p>a > 30.1</p> </td> </tr> <tr> <td> <p>Other</p> </td> <td> <p>2</p> </td> <td> <p>none of the above</p> </td> </tr> </tbody> </table> <ul> <li><strong>Production of SSO reflectance spectra</strong></li> </ul> <p>The first step in computing the SSO mean reflectance spectra consisted of a calibration of the BP/RP spectra and removal of all instrumental and astrophysical effects to produce internally calibrated epoch spectra [3]. Each of them is an array of 60 internal flux measurements and corresponding uncertainties, computed for each one of the 60 pixel-long XP (BP/RP). The BP operates in the wavelength range λ between 330 and 680 nm, and RP between 640 and 1050 nm. Next, BP and RP epoch reflectance R(λi)<sub>t</sub> were determined by dividing the flux f<sub>t</sub>(λi) of each SSO spectrum at the epoch t by the reference solar analogue spectrum F(λ). The latter has been computed by averaging Gaia DR3 mean spectra of several known solar analogue stars widely used in asteroid ground-based spectroscopy because their spectra closely mimic the one of our Sun. Epoch reflectance was then normalized at λ = 550 nm. To compute the mean reflectance spectrum, we first defined a set of fixed wavelength bands, each one having a width of 44 nm, in the interval from 374 nm to 1034 nm. Inside each wavelength band, we computed a weighted average reflectance using all epoch reflectance present in each bin after applying a sigma-clipping procedure (see Figure 1).</p> <p><img src="" alt="" width="408" height="309" /></p> <p>Figure 1: Example of the mean computed reflectance R(λi) (black circles) for the asteroid (61) Danae. The grey points are the R(λi)<sub>t</sub> corresponding to each epoch reflectance. The R(λi)<sub> t</sub> values accepted by our filtering method are coloured in blue (BP) and red (RP).</p> <p>Some filters based on SNR and on quality criteria were finally applied to the sample of computed mean reflectance spectra. Along with the mean reflectance spectra, the Gaia DR3 catalogue also contains for each source a <em>reflectance_spectrum_flag</em> field, indicating the overall quality of the resulting reflectance spectrum.</p> <ul> <li><strong>Validation</strong></li> </ul> <p>The validation of the Gaia DR3 mean reflectance spectra was obtained by studying and comparing spectral parameters including the spectral slope and the absorption band depth around 900 nm (equivalent to SDSS z-i colour) with those available in the literature, including the SMASSII survey [4] (Figure 2), ground-based observations at large phase angle [5] or space-borne telescope spectra. In general, Gaia DR3 mean reflectance spectra are in good agreement with the literature data. No significant spectral reddening was detected during the validation step.</p> <p><img src="" alt="" width="577" height="436" /></p> <p> </p> <p>Figure 2: z colour vs. spectral slope of the asteroids of DR3 (grey dots). Over-plotted with circles of different colours are the same spectral parameters computed by us (see Section 4.2) for the asteroids of SMASSII [4]. The letters C, S, and X represent taxonomic complexes, the other letters spectral classes</p> <ul> <li><strong>Conclusions</strong></li> </ul> <p>Gaia DR3 includes the largest space-based survey of reflectance spectra of Solar System small bodies observed at visible wavelengths with excell
A. Panahi; S. Zucker; G. Clementini; M. Audard; A. Binnenfeld; F. Cusano; D. W. Evans; Roy Gomel; B. Holl; I. Ilyin; G. Jévardat de Fombelle; T. Mazeh; N. Mowlavï; K. Nienartowicz; L. Rimoldini; S. Shahaf; L. Eyer
Astronomy and Astrophysics · DOI ↗
Context. The space telescope Gaia is mainly dedicated to performing high-precision astrometry but is also used to perform spectroscopy and epoch photometry, which can be used to study various types of photometric variability. One such variability type is exoplanetary transits. The photometric data accumulated so far have finally matured enough to allow the detection of some exoplanets. Aims. In order to fully exploit the scientific potential of Gaia, we search its photometric data for the signatures of exoplanetary transits. Methods. The search relies on a version of the box-fitting least-squares method, applied to a set of stars prioritized by machine-learning classification methods. An independent photometric validation was obtained using the public full-frame images of TESS. In order to validate the first two candidates, radial-velocity follow-up observations were performed using the spectrograph PEPSI of the Large Binocular Telescope. Results. The radial-velocity measurements confirm that two of the candidates are indeed hot Jupiters. Thus, they are the first exoplanets detected by Gaia: Gaia -1b and Gaia -2b. Conclusions. Gaia- 1b and Gaia- 2b demonstrate that the approach presented in this paper is indeed effective. This approach will be used to assemble a set of additional exoplanet candidates, to be released in the third Gaia data release, ensuring better fulfillment of the exoplanet detection potential of Gaia.
A. Kawash; Laura Chomiuk; Jay Strader; K. V. Sokolovsky; E. Aydi; C. S. Kochanek; K. Z. Stanek; Z. Kostrzewa-Rutkowska; S. T. Hodgkin; K. Mukai; B. J. Shappee; T. Jayasinghe; Michael Rizzo Smith; T. W. S. Holoien; J. L. Prieto; T. A. Thompson
The Astrophysical Journal · DOI ↗
Abstract We present the first estimate of the Galactic nova rate based on optical transient surveys covering the entire sky. Using data from the All-Sky Automated Survey for Supernovae (ASAS-SN) and Gaia—the only two all-sky surveys to report classical nova candidates—we find 39 confirmed Galactic novae and 7 additional unconfirmed candidates discovered from 2019 to 2021, yielding a nova discovery rate of ≈14 yr −1 . Using accurate Galactic stellar mass models and three-dimensional dust maps and incorporating realistic nova light curves, we have built a sophisticated Galactic nova model to estimate the fraction of Galactic novae discovered by these surveys over this time period. The observing capabilities of each survey are distinct: the high cadence of ASAS-SN makes it sensitive to fast novae, while the broad observing filter and high spatial resolution of Gaia make it more sensitive to highly reddened novae across the entire Galactic plane and bulge. Despite these differences, we find that ASAS-SN and Gaia give consistent Galactic nova rates, with a final joint nova rate of 26 ± 5 yr −1 . This inferred nova rate is substantially lower than found by many other recent studies. Critically assessing the systematic uncertainties in the Galactic nova rate, we argue that the role of faint, fast-fading novae has likely been overestimated, but that subtle details in the operation of transient alert pipelines can have large, sometimes unappreciated effects on transient recovery efficiency. Our predicted nova rate can be directly tested with forthcoming red/near-infrared transient surveys in the southern hemisphere.
Hans‐Walter Rix; Vedant Chandra; R. Andrae; Adrian M. Price-Whelan; David H. Weinberg; Charlie Conroy; M. Fouesneau; David W. Hogg; F. De Angeli; Rohan P. Naidu; Maosheng Xiang; D. Ruz-Mieres
The Astrophysical Journal · DOI ↗
Abstract Our Milky Way should host an ancient, metal-poor, and centrally concentrated stellar population, which reflects the star formation and enrichment in the few most massive progenitors that coalesced at high redshift to form the proto-Galaxy. While metal-poor stars are known to reside in the inner few kiloparsecs of our Galaxy, current data do not yet provide a comprehensive picture of such a metal-poor “heart” of the Milky Way. We use information from Gaia Data Release 3, especially the XP spectra, to construct a sample of 2 million bright ( G BP &lt; 15.5 mag) giant stars within 30° of the Galactic center (GC) with robust [M/H] estimates, δ [M/H] ≲ 0.1. For ∼1.25 million stars we calculate orbits from Gaia Radial Velocity Spectrometer velocities and astrometry. This sample reveals an extensive, ancient, and metal-poor population that includes ∼18,000 stars with −2.7 &lt; [M/H] &lt; −1.5, representing a stellar mass of ≳5 × 10 7 M ⊙ . The spatial distribution of these [M/H] &lt; −1.5 stars has a Gaussian extent of only <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML&quot; overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>σ</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi mathvariant="italic">R</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">GC</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> <mml:mo>∼</mml:mo> <mml:mn>2.7</mml:mn> <mml:mspace width="0.25em"/> <mml:mi>kpc</mml:mi> </mml:math> around the GC, with most orbits confined to the inner Galaxy. At high orbital eccentricities, there is clear evidence for accreted halo stars in their pericentral orbit phase. Most stars show [ α /Fe] enhancement and [Al/Fe]–[Mn/Fe] abundances expected for an origin in the more massive portions of the proto-Galaxy. Stars with [M/H] &lt; −2 show no net rotation, whereas those with [M/H] ∼ −1 are rotation dominated. These central, metal-poor stars most likely predate the oldest disk population ( τ age ≈ 12.5 Gyr), which implies that they formed at z ≳ 5, forging the proto-Milky Way.
Federico Sestito; Kim A. Venn; Anke Arentsen; David S. Aguado
Proceedings of the International Astronomical Union · DOI ↗
Abstract The investigation of the metal-poor tail in the Galactic bulge provides unique information on the early Milky Way assembly and evolution. A chemo-dynamical analysis of 17 very metal-poor stars (VMP, [Fe/H &lt; – 2.0]) selected from the Pristine Inner Galaxy Survey was carried out based on Gemini/GRACES spectra. The chemistry suggests that the majority of our stars are very similar to metal-poor stars in the Galactic halo. Orbits calculated from Gaia EDR3 imply these stars are brought into the bulge during the earliest Galactic assembly. Most of our stars have large [Na,Ca/Mg] abundances, and thus show little evidence of enrichment by pair-instability supernovae. Two of our stars (P171457, P184700) have chemical abundances compatible with second-generation globular cluster stars, suggestive of the presence of ancient and now dissolved globular clusters in the inner Galaxy. One of them (P171457) is extremely metal-poor ([Fe/H &lt; – 3.0]) and well below the metallicity floor of globular clusters, which supports the growing evidence for the existence of lower-metallicity globular clusters in the early Universe. A third star (P180956, [Fe/H]∼ – 2) has low [Na,Ca/Mg] and very low [Ba/Fe] for its metallicity, which are consistent with formation in a system polluted by only one or a few low-mass supernovae. Interestingly, its orbit is confined to the Galactic plane, like other very metal-poor stars found in the literature, which have been associated with the earliest building blocks of the Milky Way.
Federico Sestito; Kim A. Venn; Anke Arentsen; David S. Aguado; Collin Kielty; C. Lardo; Nicolas F. Martin; Julio F. Navarro; Else Starkenburg; Fletcher Waller; R. G. Carlberg; P. François; J. I. Gónzalez Hernández; G. Kordopatis; Sara Vitali; Zhen Yuan
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT The investigation of the metal-poor tail in the Galactic bulge provides unique information on the early Milky Way assembly and evolution. A chemo-dynamical analysis of 17 very metal-poor stars (VMP, [Fe/H]&amp;lt;−2.0) selected from the Pristine Inner Galaxy Survey was carried out based on Gemini/GRACES spectra. The chemistry suggests that the majority of our stars are very similar to metal-poor stars in the Galactic halo. Orbits calculated from Gaia EDR3 imply these stars are brought into the bulge during the earliest Galactic assembly. Most of our stars have large [Na,Ca/Mg] abundances, and thus show little evidence of enrichment by pair-instability supernovae. Two of our stars (P171457 and P184700) have chemical abundances compatible with second-generation globular cluster stars, suggestive of the presence of ancient and now dissolved globular clusters in the inner Galaxy. One of them (P171457) is extremely metal-poor ([Fe/H]&amp;lt;−3.0) and well below the metallicity floor of globular clusters, which supports the growing evidence for the existence of lower-metallicity globular clusters in the early Universe. A third star (P180956, [Fe/H]∼−2) has low [Na,Ca/Mg] and very low [Ba/Fe] for its metallicity, which are consistent with formation in a system polluted by only one or a few low-mass supernovae. Interestingly, its orbit is confined to the Galactic plane, like other very metal-poor stars found in the literature, which have been associated with the earliest building blocks of the Milky Way.
H. Zhao; M. Schultheis; Anke Arentsen; G. Kordopatis; M. Fouesneau; Else Starkenburg; Federico Sestito; V. Hill; Nicolas F. Martin; S. Fabbro; A. B. A. Queiroz
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT Although diffuse interstellar bands (DIBs) were discovered over 100 yr ago, for most of them, their origins are still unknown. Investigation on the correlations between different DIBs is an important way to study the behaviour and distributions of their carriers. Based on stacking thousands of spectra from the Pristine Inner Galaxy Survey, we study the correlations between two DIBs at 442.8 nm (λ442.8) and 862.1 nm (λ862.1), as well as the dust grains, in a range of latitude spanning ∼22° ($4^{\circ }\, {\lt }\, |b|\, {\lt }\, 15^{\circ }$) toward the Galactic Centre ($|\ell |\, {\lt }\, 11^{\circ }$). Tight linear intensity correlations can be found between λ442.8, λ862.1, and dust grains for $|b|\, {\lt }\, 12^{\circ }$ or $E(B\, {-}\, V)\, {\gt }\, 0.3$ mag. For $|b|\, {\gt }\, 12^{\circ }$, λ442.8 and λ862.1 present larger relative strength with respect to the dust grains. A systematic variation of the relative strength between λ442.8 and λ862.1 with |b| and $E(B\, {-}\, V)$ concludes that the two DIBs do not share a common carrier. Furthermore, the carrier of λ862.1 is more abundant at high latitudes than that of λ442.8. This work can be treated as an example showing the significance and potentials to the DIB research covering a large latitude range.
S. T. Hodgkin; D. L. Harrison; E. Breedt; T. Wevers; G. Rixon; A. Delgado; A. Yoldas; Z. Kostrzewa-Rutkowska; Ł. Wyrzykowski; M. van Leeuwen; et al.
Astronomy and Astrophysics · DOI ↗
Context. Since July 2014, the Gaia mission has been engaged in a high-spatial-resolution, time-resolved, precise, accurate astrometric, and photometric survey of the entire sky. Aims. We present the Gaia Science Alerts project, which has been in operation since 1 June 2016. We describe the system which has been developed to enable the discovery and publication of transient photometric events as seen by Gaia . Methods. We outline the data handling, timings, and performances, and we describe the transient detection algorithms and filtering procedures needed to manage the high false alarm rate. We identify two classes of events: (1) sources which are new to Gaia and (2) Gaia sources which have undergone a significant brightening or fading. Validation of the Gaia transit astrometry and photometry was performed, followed by testing of the source environment to minimise contamination from Solar System objects, bright stars, and fainter near-neighbours. Results. We show that the Gaia Science Alerts project suffers from very low contamination, that is there are very few false-positives. We find that the external completeness for supernovae, C E = 0.46, is dominated by the Gaia scanning law and the requirement of detections from both fields-of-view. Where we have two or more scans the internal completeness is C I = 0.79 at 3 arcsec or larger from the centres of galaxies, but it drops closer in, especially within 1 arcsec. Conclusions. The per-transit photometry for Gaia transients is precise to 1% at G = 13, and 3% at G = 19. The per-transit astrometry is accurate to 55 mas when compared to Gaia DR2. The Gaia Science Alerts project is one of the most homogeneous and productive transient surveys in operation, and it is the only survey which covers the whole sky at high spatial resolution (subarcsecond), including the Galactic plane and bulge.
A. G. A. Brown; A. Vallenari; T. Prusti; J. H. J. de Bruijne; C. Babusiaux; M. Biermann; O. L. Creevey; D. W. Evans; L. Eyer; A. Hutton; et al.
Astronomy and Astrophysics · DOI ↗
&lt;p&gt;ERRATUM&lt;/p&gt;&lt;p&gt;This article is an erratum for:&lt;br&gt;&lt;a href="https://www.aanda.org/10.1051/0004-6361/202039657"&gt;[https://doi.org/…;&lt;/p&gt;
D. Hobbs; Anthony Brown; E. Høg; C. Jordi; Daisuke Kawata; P. Tanga; S. A. Klioner; A. Sozzetti; Ł. Wyrzykowski; N. A. Walton; A. Vallenari; В. В. Макаров; J. Rybizki; F. Jiménez-Esteban; J. A. Caballero; P. J. McMillan; Nathan J. Secrest; R. Mor; Jeff J. Andrews; T. Zwitter; C. Chiappini; J. P. U. Fynbo; Yuan-Sen Ting; Daniel Hestroffer; L. Lindegren; B. McArthur; Naoteru Gouda; Anna Moore; O. A. González; M. Vaccari
Experimental Astronomy · DOI ↗
Abstract The era of all-sky space astrometry began with the Hipparcos mission in 1989 and provided the first very accurate catalogue of apparent magnitudes, positions, parallaxes and proper motions of 120 000 bright stars at the milliarcsec (or milliarcsec per year) accuracy level. Hipparcos has now been superseded by the results of the Gaia mission. The second Gaia data release contained astrometric data for almost 1.7 billion sources with tens of microarcsec (or microarcsec per year) accuracy in a vast volume of the Milky Way and future data releases will further improve on this. Gaia has just completed its nominal 5-year mission (July 2019), but is expected to continue in operations for an extended period of an additional 5 years through to mid 2024. Its final catalogue to be released $\sim $ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"&gt; <mml:mo>∼</mml:mo> </mml:math> 2027, will provide astrometry for $\sim $ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"&gt; <mml:mo>∼</mml:mo> </mml:math> 2 billion sources, with astrometric precisions reaching 10 microarcsec. Why is accurate astrometry so important? The answer is that it provides fundamental data which underpin much of modern observational astronomy as will be detailed in this White Paper. All-sky visible and Near-InfraRed (NIR) astrometry with a wavelength cutoff in the K-band is not just focused on a single or small number of key science cases. Instead, it is extremely broad, answering key science questions in nearly every branch of astronomy while also providing a dense and accurate visible-NIR reference frame needed for future astronomy facilities.
Adam B. Langeveld; Nikku Madhusudhan; Samuel H. C. Cabot; S. T. Hodgkin
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT Using high-resolution ground-based transmission spectroscopy to probe exoplanetary atmospheres is difficult due to the inherent telluric contamination from absorption in Earth’s atmosphere. A variety of methods have previously been used to remove telluric features in the optical regime and calculate the planetary transmission spectrum. In this paper we present and compare two such methods, specifically focusing on Na detections using high-resolution optical transmission spectra: (1) calculating the telluric absorption empirically based on the airmass and (2) using a model of the Earth’s transmission spectrum. We test these methods on the transmission spectrum of the hot Jupiter HD 189733 b using archival data obtained with the HARPS spectrograph during three transits. Using models for Centre-to-Limb Variation and the Rossiter–McLaughlin effect, spurious signals which are imprinted within the transmission spectrum are reduced. We find that correcting tellurics with an atmospheric model of the Earth is more robust and produces consistent results when applied to data from different nights with changing atmospheric conditions. We confirm the detection of sodium in the atmosphere of HD 189733 b, with doublet line contrasts of $-0.64 \pm 0.07~{{\ \rm per\ cent}}$ (D2) and $-0.53 \pm 0.07~{{\ \rm per\ cent}}$ (D1). The average line contrast corresponds to an effective photosphere in the Na line located around 1.13 Rp. We also confirm an overall blueshift of the line centroids corresponding to net atmospheric eastward winds with a speed of 1.8 ± 1.2 km s−1. Our study highlights the importance of accurate telluric removal for consistent and reliable characterization of exoplanetary atmospheres using high-resolution transmission spectroscopy.
P. Gandhi; D. A. H. Buckley; P. A. Charles; S. T. Hodgkin; Simone Scaringi; C. Knigge; A. R. Rao; John A. Paice; Yue Zhao
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT Astrometric noise (ϵ) in excess of parallax and proper motion is a potential signature of orbital wobble (ω) of individual components in binary star systems. The combination of X-ray selection with astrometric noise could then be a powerful tool for robustly isolating accreting binaries in large surveys. Here, we mine the Gaia EDR3 catalogue for Galactic sources with significant values of astrometric noise over the parameter space expected for known and candidate X-ray binaries (XRBs). Cross-matching our sample with the Chandra Source Catalogue returns a primary sample of ≈6500 X-ray sources with significant ϵ. X-ray detection efficiency for objects with significant ϵ is a factor of ≈4.5 times higher than in a matched control sample exhibiting low ϵ. The primary sample branches off the main sequence much more than control objects in colour–mag space, and includes a higher fraction of known binaries, variables, and young stellar object class types. However, values of ϵ reported in the Gaia pipeline releases so far can exceed expectations for individual XRBs with known semimajor axis size and other system parameters. It is likely that other factors (possibly attitude and modelling uncertainties, as well as source variability) currently dominate the observed excess noise in such systems. Confirmation of their nature must therefore await future Gaia releases. The full X-ray matched catalogue is released here to enable legacy follow-up.
Pascal M Keller; E. Breedt; S. T. Hodgkin; Vasily Belokurov; J. F. Wild; Ignacio García-Soriano; J. Wise
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT Gaia provided the largest ever catalogue of white dwarf stars. We use this catalogue, along with the third public data release of the Zwicky Transient Facility (ZTF), to identify new eclipsing white dwarf binaries. Our method exploits light-curve statistics and the box least-squares algorithm to detect periodic light-curve variability. The search revealed 18 new binaries, of which 17 are eclipsing. We use the position in the Gaia H-R diagram to classify these binaries and find that the majority of these white dwarfs have MS companions. We identify one system as a candidate eclipsing white dwarf–brown dwarf binary and a further two as extremely low-mass white dwarf binaries. We also provide identification spectroscopy for 17 of our 18 binaries. Running our search method on mock light curves with real ZTF sampling, we estimate our efficiency of detecting objects with light curves similar to the ones of the newly discovered binaries. Many more binaries are to be found in the ZTF footprint as the data releases grow, so our survey is ongoing.
Marco Delbò; L. Galluccio; F. De Angeli; P. Tanga; A. Cellino; Thierry Pauwels; François Mignard
Asteroids reflectance spectra in the visible light will be one of the novel products of the Gaia Data Release 3 (DR3). These spectra are produced from Gaia observations obtained by means of the blue and red photometers &amp;#8212; the so-called BP and RP, respectively. We will review the strategy adopted to produce asteroid reflectance spectra from BP-RP data, focusing on the choice of spectro-photometric calibrations computed taking into account solar system object astrometry and suitable lists of solar-analog stars.&amp;#160;Our preliminary investigation shows that we will be able to obtain reflectance spectra for asteroids as small as some km in the main belt, by exploiting the fact that each object has been observed multiple times by Gaia. We will show the capability of Gaia to probe the detailed compositional gradient of the main belt down to small sizes and to study correlations between spectral classes and other asteroid physical parameters, such as albedo and size.&amp;#160;Concerning the brightest asteroids, we expect to have substantial signal at wavelengths shorter than 450 nm, allowing Gaia to examine this region of the spectrum that has been poorly investigated by ground-based asteroid spectroscopic surveys. This region is characterised by the presence of a reflectance downturn that is diagnostic for the composition of classes of primitive asteroids, for instance those including the parent bodies of carbonaceous chondrites. These asteroids may have played an important role for the delivery of prebiotic compounds to Earth during the early phases of solar system' s history and, as such, are at the center of attention of the planetary science community.&amp;#160;
Samuel Lai; Erik Dennihy; Siyi Xu; A. Nitta; S. J. Kleinman; S. K. Leggett; Amy Bonsor; S. T. Hodgkin; A. Rebassa–Mansergas; Laura K. Rogers
The Astrophysical Journal · DOI ↗
Abstract Infrared excesses around white dwarf stars indicate the presence of various astrophysical objects of interest, including companions and debris disks. In this second paper of a series, we present follow-up observations of infrared excess candidates from Gaia and unWISE discussed in the first paper, Paper I. We report space-based infrared photometry at 3.6 and 4.5 micron for 174 white dwarfs from the Spitzer Space Telescope and ground-based near-infrared J , H , and K photometry of 235 white dwarfs from Gemini Observatory with significant overlap between Spitzer and Gemini observations. These data are used to confirm or rule out the observed unWISE infrared excess. From the unWISE-selected candidate sample, the most promising infrared excess sample comes from both color and flux excess, which has a Spitzer confirmation rate of 95%. We also discuss a method to distinguish infrared excess caused by stellar or sub-stellar companions from potential dust disks. In total, we confirm the infrared excess around 62 white dwarfs, 10 of which are likely to be stellar companions. The remaining 52 bright white dwarfs with infrared excess beyond two microns has the potential to double the known sample of white dwarfs with dusty exoplanetary debris disks. Follow-up high-resolution spectroscopic studies of a fraction of confirmed excess white dwarfs in this sample have discovered emission from gaseous dust disks. Additional investigations will be able to expand the parameter space from which dust disks around white dwarfs are found.
J. M. Carrasco; M. Weiler; C. Jordi; C. Fabricius; F. De Angeli; D. W. Evans; F. van Leeuwen; M. Riello; P. Montegriffo
Astronomy and Astrophysics · DOI ↗
Context. The full third Gaia data release will provide, for the first time, the calibrated spectra obtained with the blue and red Gaia slitless spectrophotometers (BP and RP, respectively). Gaia is a very complex mission and cannot be considered as a single instrument, but rather as many instruments. The two lines of sight with wide fields of view introduce strong variations of the observations across the large focal plane with more than one hundred different detectors. The main challenge when facing Gaia spectral calibration is that no lamp spectra or flat fields are available during the mission. Also, the significant size of the line spread function with respect to the dispersion of the prisms produces alien photons contaminating neighbouring positions of the spectra. This makes the calibration special and different from standard approaches. Aims. This work gives a detailed description of the internal calibration model for the spectrophotometric data used to obtain the content of the Gaia catalogue. The main purpose of the internal calibration is to bring all the epoch spectra onto a common flux and pixel (pseudo-wavelength) scale, taking into account variations over the focal plane and with time, producing a mean spectrum from all the observations of the same source. Methods. In order to describe all observations on a common mean flux and pseudo-wavelength scale, we constructed a suitable representation of the internally calibrated mean spectra via basis functions, and we described the transformation between non-calibrated epoch spectra and calibrated mean spectra via a discrete convolution, parametrising the convolution kernel to recover the relevant coefficients. Results. The model proposed here for the internal calibration of the Gaia spectrophotometric observations is able to combine all observations into a mean instrument to allow the comparison of different sources and observations obtained with different instrumental conditions along the mission and the generation of mean spectra from a number of observations of the same source. We derived a calibration model that can handle the self-calibrating nature of the problem. The output of this model provides the internal mean spectra, not as a sampled function (flux and wavelength), but as a linear combination of basis functions, although sampled spectra can easily be derived from them.
N. Mowlavï; L. Rimoldini; D. W. Evans; M. Riello; F. De Angeli; L. Palaversa; M. Audard; L. Eyer; P. García-Lario; P. Gavras; B. Holl; G. Jévardat de Fombelle; I. Lecœur-Taı̈bi; K. Nienartowicz
Astronomy and Astrophysics · DOI ↗
Context. Photometric variability is an essential feature that sheds light on the intrinsic properties of celestial variable sources, the more so when photometry is available in various bands. In this respect, the all-sky Gaia mission is particularly attractive as it collects, among other quantities, epoch photometry measured quasi-simultaneously in three optical bands for sources ranging from a few magnitudes to fainter than magnitude 20. Aims. The second data release (DR2) of the mission provides mean G , G BP , and G RP photometry for ∼1.4 billion sources, but light curves and variability properties are available for only ∼0.5 million of them. Here, we provide a census of large-amplitude variables (LAVs) with amplitudes larger than ∼0.2 mag in the G band for objects with mean brightnesses between 5.5 and 19 mag. Methods. To achieve this, we rely on variability amplitude proxies in G , G BP , and G RP computed from the uncertainties on the magnitudes published in DR2. We then apply successive filters to identify two subsets containing sources with reliable mean G BP and G RP (for studies using colours) and sources having compatible amplitude proxies in G , G BP , and G RP (for multi-band variability studies). Results. The full catalogue gathers 23 315 874 LAV candidates, and the two subsets with increased levels of purity contain, respectively, 1 148 861 and 618 966 sources. A multi-band variability analysis of the catalogue shows that different types of variable stars can be categorized according to their colours and blue-to-red amplitude ratios as determined from the G , G BP , and G RP amplitude proxies. More specifically, four groups are globally identified. They include: long-period variables in a first group with amplitudes more than twice larger in the blue than in the red; hot compact variables in a second group with amplitudes smaller in the blue than in the red; classical instability strip pulsators in a third group with amplitudes larger in the blue than in the red by 50% to 80%; and other non-pulsating variables in a fourth group, mainly achromatic, but 10% of them still having 20% to 50% larger amplitudes in the blue than in the red. Conclusions. The catalogue constitutes the first census of Gaia LAV candidates extracted from the public DR2 archive. The overview presented here illustrates the added value of the mission for multi-band variability studies, even at this stage when epoch photometry is not yet available for all sources.
Rosanna H Tilbrook; M. R. Burleigh; Jean C Costes; Samuel Gill; Louise D. Nielsen; José I Vines; D. Queloz; S. T. Hodgkin; Hannah L. Worters; M. R. Goad; Jack S Acton; Beth A Henderson; D. J. Armstrong; D. R. Anderson; Daniel Bayliss; F. Bouchy; Joshua T Briegal; Edward M. Bryant; S. L. Casewell; Alexander Chaushev; Benjamin F Cooke; Philipp Eigmüller; Edward Gillen; Maximilian N. Günther; Aleisha Hogan; J. S. Jenkins; M. Lendl; J. McCormac; Maximiliano Moyano; Liam Raynard; A. M. S. Smith; S. Udry; C. A. Watson; R. G. West; P. J. Wheatley; H. Breytenbach; Ramotholo Sefako; Jessymol K Thomas; D. R. Alves
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT We report the discovery of four new hot Jupiters with the Next-Generation Transit Survey (NGTS). NGTS-15b, NGTS-16b, NGTS-17b, and NGTS-18b are short-period (P &amp;lt; 5 d) planets orbiting G-type main-sequence stars, with radii and masses between 1.10 and 1.30RJ and 0.41 and 0.76MJ, respectively. By considering the host star luminosities and the planets’ small orbital separations (0.039–0.052 au), we find that all four hot Jupiters are highly irradiated and therefore occupy a region of parameter space in which planetary inflation mechanisms become effective. Comparison with statistical studies and a consideration of the planets’ high incident fluxes reveal that NGTS-16b, NGTS-17b, and NGTS-18b are indeed likely inflated, although some disparities arise upon analysis with current Bayesian inflationary models. However, the underlying relationships that govern radius inflation remain poorly understood. We postulate that the inclusion of additional hyperparameters to describe latent factors such as heavy element fraction, as well as the addition of an updated catalogue of hot Jupiters, would refine inflationary models, thus furthering our understanding of the physical processes that give rise to inflated planets.
N. Chornay; N. A. Walton
Astronomy and Astrophysics · DOI ↗
Context. Planetary nebulae (PNe) are a brief but important phase of stellar evolution. The study of Galactic PNe has historically been hampered by uncertain distances, but the parallaxes of PN central stars (CSPNe) measured by Gaia are improving the situation. Aims. Gaia ’s Early Data Release 3 (EDR3) offers higher astrometric precision and greater completeness compared to previous releases. Taking advantage of these improvements requires that the CSPNe in the catalogue be accurately identified. Methods. We applied our automated technique based on the likelihood ratio method to cross-match known PNe with sources in Gaia EDR3, using an empirically derived position and colour distribution to score candidate matches. Results. We present a catalogue of over 2000 sources in Gaia EDR3 that our method has identified as likely CSPNe or compact nebula detections. We show how the more precise parallaxes of these sources compare to previous PN statistical distances and introduce an approach to combining them to produce tighter distance constraints. We also discuss Gaia ’s handling of close companions and bright nebulae. Conclusions. Gaia is unlocking new avenues for the study of PNe. The catalogue presented here will remain valid for the upcoming Gaia Data Release 3 (DR3) and thus provide a valuable resource for years to come.