Alexandra L Gregory; Michelle Collins; Justin I. Read; M. J. Irwin; Rodrigo Ibata; Nicolas F. Martin; Alan W. McConnachie; Daniel R. Weisz
Monthly Notices of the Royal Astronomical Society · DOI
We present new FLAMES+GIRAFFE spectroscopy of 36 member stars in the isolated Local Group dwarf spheroidal galaxy Tucana. We measure a systemic velocity for the system of v Tuc = 216.7 +2.9
Laura K. Rogers; Siyi Xu; Amy Bonsor; S. T. Hodgkin; K. Y. L. Su; Ted von Hippel; Michael Jura
Proceedings of the International Astronomical Union · DOI
Abstarct Planetary material in the atmospheres of white dwarfs is thought to be scattered inwards from outer planetary systems. Dusty emission in the infrared traces the accretion. As the scattering of many small asteroids is a stochastic process, variability in the infrared emission is predicted. We report a 3 year near-infrared ( J , H and K ) monitoring campaign of 34 dusty, polluted white dwarfs which aims to search for dust emission variability. We find all white dwarfs have consistent near-infrared fluxes, implying the excess emission is stable. This suggests tidal disruption events which lead to large variabilities are rare and quick (<1 year) and become stable within a few years. For WD 0408–041, the system that shows both increases and decreases in dust emission over 11 years, our K band data suggest a potential colour change associated with the dust emission that needs further confirmation.
Edward Gillen; Joshua T Briegal; S. T. Hodgkin; Daniel Foreman-Mackey; Floor Van Leeuwen; James A. G. Jackman; J. McCormac; R. G. West; D. Queloz; Daniel Bayliss; M. R. Goad; C. A. Watson; P. J. Wheatley; Claudia Belardi; M. R. Burleigh; S. L. Casewell; J. S. Jenkins; Liam Raynard; A. M. S. Smith; Rosanna H Tilbrook; José I Vines
Monthly Notices of the Royal Astronomical Society · DOI
ABSTRACT We determine rotation periods for 127 stars in the ∼115-Myr-old Blanco 1 open cluster using ∼200 d of photometric monitoring with the Next Generation Transit Survey. These stars span F5–M3 spectral types (1.2 M⊙ ≳ M ≳ 0.3 M⊙) and increase the number of known rotation periods in Blanco 1 by a factor of four. We determine rotation periods using three methods: Gaussian process (GP) regression, generalized autocorrelation function (G-ACF), and Lomb–Scargle (LS) periodogram, and find that the GP and G-ACF methods are more applicable to evolving spot modulation patterns. Between mid-F and mid-K spectral types, single stars follow a well-defined rotation sequence from ∼2 to 10 d, whereas stars in photometric multiple systems typically rotate faster. This may suggest that the presence of a moderate-to-high mass ratio companion inhibits angular momentum loss mechanisms during the early pre-main sequence, and this signature has not been erased at ∼100 Myr. The majority of mid-F to mid-K stars display evolving modulation patterns, whereas most M stars show stable modulation signals. This morphological change coincides with the shift from a well-defined rotation sequence (mid-F to mid-K stars) to a broad rotation period distribution (late-K and M stars). Finally, we compare our rotation results for Blanco 1 to the similarly aged Pleiades: the single-star populations in both clusters possess consistent rotation period distributions, which suggests that the angular momentum evolution of stars follows a well-defined pathway that is, at least for mid-F to mid-K stars, strongly imprinted by ∼100 Myr.
R. G. West; Edward Gillen; Daniel Bayliss; M. R. Burleigh; L. Delrez; Maximilian N. Günther; S. T. Hodgkin; James A. G. Jackman; J. S. Jenkins; George W. King; J. McCormac; Louise D. Nielsen; Liam Raynard; A. M. S. Smith; M. G. Soto; Oliver Turner; P. J. Wheatley; Yaseen Almleaky; D. J. Armstrong; Claudia Belardi; F. Bouchy; Joshua T Briegal; Artem Burdanov; Juan Cabrera; S. L. Casewell; Alexander Chaushev; Bruno Chazelas; P. Chote; Benjamin F Cooke; Szilárd Csizmadia; Elsa Ducrot; Philipp Eigmüller; A. Erikson; Emma Foxell; B. T. Gänsicke; M. Gillon; M. R. Goad; Emmanuël Jehin; Gregory Lambert; Emma Longstaff; Tom Louden; Maximiliano Moyano; C. A. Murray; D. Pollacco; D. Queloz; H. Rauer; Sandrine Sohy; Samantha Thompson; S. Udry; S. R. Walker; C. A. Watson
Monthly Notices of the Royal Astronomical Society · DOI
We report the discovery of NGTS-4b, a sub-Neptune-sized planet transiting a 13th magnitude K-dwarf in a 1.34 d orbit. NGTS-4b has a mass M = 20.6 3.0 M and radius R = 3.18 0.26 R , which places it well within the so-called 'Neptunian Desert'. The mean density of the planet (3.45 0.95 g cm -3 ) is consistent with a composition of 100 per cent H 2 O or a rocky core with a volatile envelope. NGTS-4b is likely to suffer significant mass loss due to relatively strong EUV/X-ray irradiation. Its survival in the Neptunian desert may be due to an unusually high-core mass, or it may have avoided the most intense X-ray irradiation by migrating after the initial activity of its host star had subsided. With a transit depth of 0.13 0.02 per cent, NGTS-4b represents the shallowest transiting system ever discovered from the ground, and is the smallest planet discovered in a wide-field ground-based photometric survey.
James A. G. Jackman; P. J. Wheatley; Daniel Bayliss; Samuel Gill; S. T. Hodgkin; M. R. Burleigh; I. P. Braker; Maximilian N. Günther; Tom Louden; Oliver Turner; D. R. Anderson; Claudia Belardi; F. Bouchy; Joshua T Briegal; Edward M. Bryant; Juan Cabrera; S. L. Casewell; Alexander Chaushev; Jean C Costes; Szilárd Csizmadia; Philipp Eigmüller; A. Erikson; B. T. Gänsicke; Edward Gillen; M. R. Goad; J. S. Jenkins; J. McCormac; Maximiliano Moyano; Louise D. Nielsen; D. Pollacco; Katja Poppenhaeger; D. Queloz; H. Rauer; Liam Raynard; A. M. S. Smith; S. Udry; José I Vines; C. A. Watson; R. G. West
Monthly Notices of the Royal Astronomical Society · DOI
ABSTRACT We present the discovery of NGTS-7Ab, a high-mass brown dwarf transiting an M dwarf with a period of 16.2 h, discovered as part of the Next Generation Transit Survey (NGTS). This is the shortest period transiting brown dwarf around a main or pre-main sequence star to date. The M star host (NGTS-7A) has an age of roughly 55 Myr and is in a state of spin–orbit synchronization, which we attribute to tidal interaction with the brown dwarf acting to spin-up the star. The host star is magnetically active and shows multiple flares across the NGTS and follow-up light curves, which we use to probe the flare–star-spot phase relation. The host star also has an M star companion at a separation of 1.13 arcsec with very similar proper motion and systemic velocity, suggesting that the NGTS-7 system is a hierarchical triple. The combination of tidal synchronisation and magnetic braking is expected to drive on-going decay of the brown dwarf orbit, with a remaining lifetime of only 5–10 Myr.
Sakurako Okamoto; N. Arimoto; A. M. N. Ferguson; M. J. Irwin; Edouard J. Bernard; Yousuke Utsumi
The Astrophysical Journal · DOI
International audience
L. Galluccio; Marco Delbò; A. Cellino; P. Tanga; F. De Angeli
HAL (Le Centre pour la Communication Scientifique Directe)
International audience
Ian D. Howarth; F. van Leeuwen
Monthly Notices of the Royal Astronomical Society · DOI
We scrutinize the Hipparcos parallax for the bright O supergiant ζ Pup, and confirm that the implied distance of 332 ± 11 pc appears to be reliable. We then review the implications for the star’s physical parameters, and the consequences for the interpretation of Pphot, the 1.78-d photometric period. The equatorial rotation period is <3.7 d (with 95% confidence), ruling out a proposed ∼5.1-d value. If the photometric period is the rotation period then i, the inclination of the rotation axis to the line of sight, is 33.⁰2 ± 1.⁰8. The inferred mass, radius, and luminosity are securely established to be less than canonical values for the spectral type, and are not in agreement with single-star evolution models. The runaway status, rapid rotation, and anomalous physical properties are all indicative of an evolutionary history involving binary (or multiple-star) interaction. We perform simple starspot modelling to show that the low axial inclination required if Prot = 1.78 d has testable spectroscopic consequences, which have not been identified in existing time series. If Pphot is directly related to drivers of systematic, high-velocity stellar-wind variability (‘discrete absorption components’) in ζ Pup, antisolar differential rotation is required. Model line profiles calculated on that basis are at variance with observations.
Dougal Mackey; A. M. N. Ferguson; Avon Huxor; J. Veljanoski; Geraint F. Lewis; Alan W. McConnachie; Nicolas F. Martin; Rodrigo Ibata; M. J. Irwin; Patrick Côté; Michelle Collins; N. R. Tanvir; N. F. Bate
Monthly Notices of the Royal Astronomical Society · DOI
We utilize the final catalogue from the Pan-Andromeda Archaeological Survey to investigate the links between the globular cluster system and field halo in M31 at projected radii Rproj = 25–150 kpc. In this region the cluster radial density profile exhibits a power-law decline with index Γ = −2.37 ± 0.17, matching that for the stellar halo component with [Fe/H] < −1.1. Spatial density maps reveal a striking correspondence between the most luminous substructures in the metal-poor field halo and the positions of many globular clusters. By comparing the density of metal-poor halo stars local to each cluster with the azimuthal distribution at commensurate radius, we reject the possibility of no correlation between clusters and field overdensities at $99.95{{\ \rm per\ cent}}$ significance. We use our stellar density measurements and previous kinematic data to demonstrate that ${\approx }35\hbox{--}60{{\ \rm per\ cent}}$ of clusters exhibit properties consistent with having been accreted into the outskirts of M31 at late times with their parent dwarfs. Conversely, at least ${\sim }40{{\ \rm per\ cent}}$ of remote clusters show no evidence for a link with halo substructure. The radial density profile for this subgroup is featureless and closely mirrors that observed for the apparently smooth component of the metal-poor stellar halo. We speculate that these clusters are associated with the smooth halo; if so, their properties appear consistent with a scenario where the smooth halo was built up at early times via the destruction of primitive satellites. In this picture the entire M31 globular cluster system outside Rproj = 25 kpc comprises objects accumulated from external galaxies over a Hubble time of growth.
N. Chornay; N. A. Walton
Zenodo (CERN European Organization for Nuclear Research) · DOI
Slides presented at ESLAB 53: The Gaia Universe.
D. W. Evans; M. Riello; F. De Angeli; J. M. Carrasco; P. Montegriffo; C. Fabricius; C. Jordi; L. Palaversa; C. Diener; G. Busso; C. Cacciari; F. van Leeuwen; P. W. Burgess; M. Davidson; D. L. Harrison; S. T. Hodgkin; E. Pancino; P. J. Richards; G. Altavilla; L. Balaguer-Núñez; M. A. Barstow; M. Bellazzini; A. G. A. Brown; M. Castellani; G. Cocozza; F. De Luise; A. Delgado; C. Ducourant; S. Galleti; G. Gilmore; G. Giuffrida; B. Holl; A. Kewley; S. E. Koposov; S. Marinoni; P. M. Marrese; P. Osborne; A. M. Piersimoni; J. Portell; L. Pulone; S. Ragaini; N. Sanna; D. Terrett; N. A. Walton; T. Wevers; Ł. Wyrzykowski
Astronomy and Astrophysics · DOI
Aims. We describe the photometric content of the second data release of the Gaia project ( Gaia DR2) and its validation along with the quality of the data. Methods. The validation was mainly carried out using an internal analysis of the photometry. External comparisons were also made, but were limited by the precision and systematics that may be present in the external catalogues used. Results. In addition to the photometric quality assessment, we present the best estimates of the three photometric passbands. Various colour-colour transformations are also derived to enable the users to convert between the Gaia and commonly used passbands. Conclusions. The internal analysis of the data shows that the photometric calibrations can reach a precision as low as 2 mmag on individual CCD measurements. Other tests show that systematic effects are present in the data at the 10 mmag level.
A. G. A. Brown; A. Vallenari; T. Prusti; J. H. J. de Bruijne; C. Babusiaux; C. A. L. Bailer-Jones; M. Biermann; D. W. Evans; L. Eyer; F. Jansen; et al.
Astronomy and Astrophysics · DOI
Context. We present the second Gaia data release, Gaia DR2, consisting of astrometry, photometry, radial velocities, and information on astrophysical parameters and variability, for sources brighter than magnitude 21. In addition epoch astrometry and photometry are provided for a modest sample of minor planets in the solar system. Aims. A summary of the contents of Gaia DR2 is presented, accompanied by a discussion on the differences with respect to Gaia DR1 and an overview of the main limitations which are still present in the survey. Recommendations are made on the responsible use of Gaia DR2 results. Methods. The raw data collected with the Gaia instruments during the first 22 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into this second data release, which represents a major advance with respect to Gaia DR1 in terms of completeness, performance, and richness of the data products. Results. Gaia DR2 contains celestial positions and the apparent brightness in G for approximately 1.7 billion sources. For 1.3 billion of those sources, parallaxes and proper motions are in addition available. The sample of sources for which variability information is provided is expanded to 0.5 million stars. This data release contains four new elements: broad-band colour information in the form of the apparent brightness in the G BP (330–680 nm) and G RP (630–1050 nm) bands is available for 1.4 billion sources; median radial velocities for some 7 million sources are presented; for between 77 and 161 million sources estimates are provided of the stellar effective temperature, extinction, reddening, and radius and luminosity; and for a pre-selected list of 14 000 minor planets in the solar system epoch astrometry and photometry are presented. Finally, Gaia DR2 also represents a new materialisation of the celestial reference frame in the optical, the Gaia -CRF2, which is the first optical reference frame based solely on extragalactic sources. There are notable changes in the photometric system and the catalogue source list with respect to Gaia DR1, and we stress the need to consider the two data releases as independent. Conclusions. Gaia DR2 represents a major achievement for the Gaia mission, delivering on the long standing promise to provide parallaxes and proper motions for over 1 billion stars, and representing a first step in the availability of complementary radial velocity and source astrophysical information for a sample of stars in the Gaia survey which covers a very substantial fraction of the volume of our galaxy.
M. Riello; F. De Angeli; D. W. Evans; G. Busso; N. C. Hambly; M. Davidson; P. W. Burgess; P. Montegriffo; P. Osborne; A. Kewley; J. M. Carrasco; C. Fabricius; C. Jordi; C. Cacciari; F. van Leeuwen; G. Holland
Astronomy and Astrophysics · DOI
Context. The second Gaia data release is based on 22 months of mission data with an average of 0.9 billion individual CCD observations per day. A data volume of this size and granularity requires a robust and reliable but still flexible system to achieve the demanding accuracy and precision constraints that Gaia is capable of delivering. Aims. We aim to describe the input data, the treatment of blue photometer/red photometer (BP/RP) low-resolution spectra required to produce the integrated G BP and G RP fluxes, the process used to establish the internal Gaia photometric system, and finally, the generation of the mean source photometry from the calibrated epoch data for Gaia DR2. Methods. The internal Gaia photometric system was initialised using an iterative process that is solely based on Gaia data. A set of calibrations was derived for the entire Gaia DR2 baseline and then used to produce the final mean source photometry. The photometric catalogue contains 2.5 billion sources comprised of three different grades depending on the availability of colour information and the procedure used to calibrate them: 1.5 billion gold, 144 million silver, and 0.9 billion bronze. These figures reflect the results of the photometric processing; the content of the data release will be different due to the validation and data quality filters applied during the catalogue preparation. The photometric processing pipeline, PhotPipe, implements all the processing and calibration workflows in terms of Map/Reduce jobs based on the Hadoop platform. This is the first example of a processing system for a large astrophysical survey project to make use of these technologies. Results. The improvements in the generation of the integrated G –band fluxes, in the attitude modelling, in the cross-matching, and and in the identification of spurious detections led to a much cleaner input stream for the photometric processing. This, combined with the improvements in the definition of the internal photometric system and calibration flow, produced high-quality photometry. Hadoop proved to be an excellent platform choice for the implementation of PhotPipe in terms of overall performance, scalability, downtime, and manpower required for operations and maintenance.
T. Antoja; A. Helmi; M. Romero-Gómez; D. Katz; C. Babusiaux; R. Drimmel; D. W. Evans; F. Figueras; E. Poggio; C. Reylé; A. C. Robin; G. M. Seabroke; C. Soubiran
Nature · DOI
B. Letarte; V. Hill; Eline Tolstoy; P. Jablonka; Matthew Shetrone; Kim A. Venn; M. Spite; M. J. Irwin; G. Battaglia; A. Helmi; F. Primas; P. François; A. Kaufer; T. Szeifert; N. Arimoto; Kunihiko Sadakane
Astronomy and Astrophysics · DOI
International audience
L. Rimoldini; L. Eyer; N. Mowlavï; Dafydd Wyn Evans; K. Nienartowicz; B. Holl; M. Audard; L. P. Guy; G. Jévardat de Fombelle; Lecoeur-Taïbi, Isabelle; O. Marchal; G. Clementini; V. Ripepi; A. Garofalo; R. Molinaro; T. Muraveva; Ennio Poretti; Laszlo Molnar; E. Plachy; Áron L. Juhász; L. Szabados; J. De Ridder; S. Regibo; L. M. Sarro Baro; M. López del Fresno
arXiv (Cornell University) · DOI
The second Gaia data release is expected to contain data products from about 22 months of observation. Based on these data, we aim to provide an advance publication of a full-sky Gaia map of RR Lyrae stars. Although comprehensive, these data still contain a significant fraction of sources which are insufficiently sampled for Fourier series decomposition of the periodic light variations. The challenges in the identification of RR Lyrae candidates with (much) fewer than 20 field-of-view transits are described. General considerations of the results, their limitations, and interpretation are presented together with prospects for improvement in subsequent Gaia data releases.
Grant M. Kennedy; Gregory A. Hope; S. T. Hodgkin; M. C. Wyatt
Monthly Notices of the Royal Astronomical Society · DOI
This paper discusses an algorithm for detecting single transits in photometric time-series data. Specifically, we aim to identify asymmetric transits with ingress that is more rapid than egress, as expected for cometary bodies with a significant tail. The algorithm is automated, so can be applied to large samples and only a relatively small number of events need to be manually vetted. We applied this algorithm to all long-cadence light curves from the Kepler mission, finding 16 candidate transits with significant asymmetry, 11 of which were found to be artefacts or symmetric transits after manual inspection. Of the five remaining events, four are the 0.1 per cent depth events previously identified for KIC 3542116 and 11084727. We identify HD 182952 (KIC 8027456) as a third system showing a potential comet transit. All three stars showing these events have H–R diagram locations consistent with ∼100 Myr-old open cluster stars, as might be expected given that cometary source regions deplete with age, and giving credence to the comet hypothesis. If these events are part of the same population of events as seen for KIC 8462852, the small increase in detections at 0.1 per cent depth compared to 10 per cent depth suggests that future work should consider whether the distribution is naturally flat, or if comets with symmetric transits in this depth range remain undiscovered. Future searches relying on asymmetry should be more successful if they focus on larger samples and young stars, rather than digging further into the noise.
Christina Hedges; S. T. Hodgkin; Grant M. Kennedy
Monthly Notices of the Royal Astronomical Society · DOI
In recent years a new class of Young Stellar Object has been defined, referred to as dippers, where large transient drops in flux are observed. These dips are too large to be attributed to stellar variability, last from hours to days and can reduce the flux of a star by 10-50%. This variability has been attributed to occultations by warps or accretion columns near the inner edge of circumstellar disks. Here we present 95 dippers in the Upper Scorpius association and Ophiuchus cloud complex found in K2 Campaign 2 data using supervised machine learning with a Random Forest classifier. We also present 30 YSOs that exhibit brightening events on the order of days, known as bursters. Not all dippers and bursters are known members, but all exhibit infrared excesses and are consistent with belonging to either of the two young star forming regions. We find 21.0 5.5% of stars with disks are dippers for both regions combined. Our entire dipper sample consists only of late-type (KM) stars, but we show that biases limit dipper discovery for earlier spectral types. Using the dipper properties as a proxy, we find that the temperature at the inner disk edge is consistent with interferometric results for similar and earlier type stars.
B. Holl; M. Audard; K. Nienartowicz; G. Jevardat de Fombelle; O. Marchal; N. Mowlavï; G. Clementini; J. De Ridder; Dafydd Wyn Evans; L. P. Guy; A. C. Lanzafame; T. Lebzelter; L. Rimoldini; M. Roelens; S. Zucker; E. Distefano; A. Garofalo; I. Lecoeur-Taïbi; M. Lopez; R. Molinaro; T. Muraveva; A. Panahi; S. Regibo; V. Ripepi; Luis Manuel Sarro; Conny Aerts; R. I. Anderson; J. Charnas; F. Barblan; Sergi Blanco-Cuaresma; G. Busso; J. Cuypers; F. De Angeli; F. Glass; M. Grenon; Á. L. Juhász; A. Kochoska; P. Koubsky; Antonino Francesco Lanza; S. Leccia; D. Lorenz; Marcella Marconi; G. Marschalkó; T. Mazeh; S. Messina; F. Mignard; Andre Moitinho; Laszlo Molnar; S. Morgenthaler; I. Musella; Christophe Ordenovic; D. Ordóñez; I. Pagano; L. Palaversa; M. Pawlak; E. Plachy; A. Prša; M. Riello; M. Süveges; L. Szabados; E. Szegedi-Elek; V. Votruba; L. Eyer
Astronomy and Astrophysics · DOI
Context. The Gaia Data Release 2 (DR2) contains more than half a million sources that are identified as variable stars. Aims. We summarise the processing and results of the identification of variable source candidates of RR Lyrae stars, Cepheids, long-period variables (LPVs), rotation modulation (BY Dra-type) stars, δ Scuti and SX Phoenicis stars, and short-timescale variables. In this release we aim to provide useful but not necessarily complete samples of candidates. Methods. The processed Gaia data consist of the G, GBP, and GRP photometry during the first 22 months of operations as well as positions and parallaxes. Various methods from classical statistics, data mining, and time-series analysis were applied and tailored to the specific properties of Gaia data, as were various visualisation tools to interpret the data. Results. The DR2 variability release contains 228 904 RR Lyrae stars, 11 438 Cepheids, 151 761 LPVs, 147 535 stars with rotation modulation, 8882 δ Scuti and SX Phoenicis stars, and 3018 short-timescale variables. These results are distributed over a classification and various Specific Object Studies tables in the Gaia archive, along with the three-band time series and associated statistics for the underlying 550 737 unique sources. We estimate that about half of them are newly identified variables. The variability type completeness varies strongly as a function of sky position as a result of the non-uniform sky coverage and intermediate calibration level of these data. The probabilistic and automated nature of this work implies certain completeness and contamination rates that are quantified so that users can anticipate their effects. Thismeans that even well-known variable sources can be missed or misidentified in the published data. Conclusions. The DR2 variability release only represents a small subset of the processed data. Future releases will include more variable sources and data products; however, DR2 shows the (already) very high quality of the data and great promise for variability studies.
C. Babusiaux; Floor van Leeuwen; Martin Adrian Barstow; C. Jordi; Antonella Vallenari; D. Bossini; Alessandro Bressan; T. Cantat-Gaudin; M. van Leeuwen; A. G. A. Brown; et al.
Astronomy and Astrophysics · DOI
Context. Gaia Data Release 2 provides high-precision astrometry and three-band photometry for about 1.3 billion sources over the full sky. The precision, accuracy, and homogeneity of both astrometry and photometry are unprecedented. Aims. We highlight the power of the Gaia DR2 in studying many fine structures of the Hertzsprung-Russell diagram (HRD). Gaia allows us to present many different HRDs, depending in particular on stellar population selections. We do not aim here for completeness in terms of types of stars or stellar evolutionary aspects. Instead, we have chosen several illustrative examples. Methods. We describe some of the selections that can be made in Gaia DR2 to highlight the main structures of the Gaia HRDs. We select both field and cluster (open and globular) stars, compare the observations with previous classifications and with stellar evolutionary tracks, and we present variations of the Gaia HRD with age, metallicity, and kinematics. Late stages of stellar evolution such as hot subdwarfs, post-AGB stars, planetary nebulae, and white dwarfs are also analysed, as well as low-mass brown dwarf objects. Results. The Gaia HRDs are unprecedented in both precision and coverage of the various Milky Way stellar populations and stellar evolutionary phases. Many fine structures of the HRDs are presented. The clear split of the white dwarf sequence into hydrogen and helium white dwarfs is presented for the first time in an HRD. The relation between kinematics and the HRD is nicely illustrated. Two different populations in a classical kinematic selection of the halo are unambiguously identified in the HRD. Membership and mean parameters for a selected list of open clusters are provided. They allow drawing very detailed cluster sequences, highlighting fine structures, and providing extremely precise empirical isochrones that will lead to more insight in stellar physics. Conclusions. Gaia DR2 demonstrates the potential of combining precise astrometry and photometry for large samples for studies in stellar evolution and stellar population and opens an entire new area for HRD-based studies.