We study the stellar kinematic properties and spatial distribution of the association Cyg OB3 using precise astrometric data from Gaia DR2. All known O- and B-type stars in Cyg OB3 region with positions, parallaxes and proper motions available are included, comprising a total of 41 stars. The majority of stars are found to be concentrated at a heliocentric distance of 2.0 +/- 0.3 kpc. The mean peculiar velocity of the sample after removing Galactic rotation and solar motion is ~22 km/s, dominated by the velocity component towards the Galactic center. The relative position and velocity of the black hole X-ray binary Cyg X-1 with respect to the association suggest that Cyg OB3 is most likely its parent association. The peculiar kinematic properties of some of the stars are revealed and are suggestive of past stellar encounters. The sample includes a previously known runaway star HD 227018, and its high peculiar velocity of ~50 km/s is confirmed with Gaia. We estimated the velocities of stars relative to the association and the star HD 225577 exhibits peculiar velocity smaller than its velocity relative to the association. The star has lower value of proper motion than the rest of the sample. The results suggest a slowly expanding nature of the association, which is supported by the small relative speeds <20 km/s with respect to the association for a majority of the sample stars.
For the first time, we have explored the spatial substructure of the Cygnus OB2 association using parallaxes from the recent second Gaia data release. We find significant line-of-sight substructure within the association, which we quantify using a parameterised model that reproduces the observed parallax distribution. This inference approach is necessary due to the non-linearity of the parallax-distance transformation and the asymmetry of the resulting probability distribution. By using a Markov Chain Monte Carlo ensemble sampler and an unbinned maximum likelihood test we identify two differen…
The Cygnus OB2 Association is one of the nearest and largest collections of massive stars in the Galaxy. Situated at the heart of the "Cygnus X" complex of star-forming regions and molecular clouds, its distance has proven elusive owing to the ambiguous nature of kinematic distances along this $\ell\simeq80$ degree sightline and the heavy, patchy extinction. In an effort to refine the three-dimensional geometry of key Cygnus~X constituents, we have measured distances to four eclipsing double-lined OB-type spectroscopic binaries that are probable members of Cyg~OB2. We find distances of $1.33\p…
OB associations are the prime star forming sites in galaxies. However the detailed formation process of such stellar systems still remains a mystery. In this context, identifying the presence of substructures may help tracing the footprints of their formation process. Here, we present a kinematic study of the two massive OB associations Cygnus OB2 and Carina OB1 using the precise astrometry from the Gaia Data Release 2 and radial velocities. From the parallaxes of stars, these OB associations are confirmed to be genuine stellar systems. Both Cygnus OB2 and Carina OB1 are composed of a few dens…
The main objective of this study is the characterization of the velocity field in the Cygnus OB1 association using the radial velocity data currently available in the literature. This association is part of a larger star-forming complex located in the direction of the Cygnus region, but whose main subsystems may be distributed at different distances from the sun. We have collected radial velocity data for more than 300 stars in the area of 5 x 5 square degrees centred on the Cygnus OB1 association. We present the results of a kinematic clustering analysis in the subspace of the phase space for…
We present a high-precision proper motion study of 873 X-ray and spectroscopically selected stars in the massive OB association Cygnus OB2 as part of the DANCe project. These were calculated from images spanning a 15 year baseline and have typical precisions < 1 mas/yr. We calculate the velocity dispersion in the two axes to be $σ_α(c) = 13.0^{+0.8}_{-0.7}$ and $σ_δ(c) = 9.1^{+0.5}_{-0.5}$ km/s, using a 2-component, 2-dimensional model that takes into account the uncertainties on the measurements. This gives a 3-dimensional velocity dispersion of $σ_{3D} = 17.8 \pm 0.6$ km/s implying a virial …
Two star-forming regions are studied: the young embedded open cluster vdB 130 and the protocluster neighbourhood observed in the head and tail of the cometary molecular cloud located in the wall of the expanding supershell surrounding the Cyg OB1 association. The GAIA DR2 catalogue is employed to verify the stellar composition of the vdB 130 cluster whose members were earlier selected using the UCAC4 catalogue. The new sample of vdB 130 members contains 68 stars with close proper motions (within 1 mas yr$^{-1}$) and close trigonometric parallaxes (ranging from 0.50 to 0.70 mas). The relative p…
We examine substructure and mass segregation in the massive OB association Cygnus OB2 to better understand its initial conditions. Using a well understood Chandra X-ray selected sample of young stars we find that Cyg OB2 exhibits considerable physical substructure and has no evidence for mass segregation, both indications that the association is not dynamically evolved. Combined with previous kinematical studies we conclude that Cyg OB2 is dynamically very young, and what we observe now is very close to its initial conditions: Cyg OB2 formed as a highly substructured, unbound association with …
Aiming to explore weak spectral features of stellar and interstellar origin we used the NES echelle spectrograph of the 6-m telescope to obtain high-resolution spectra for 13 hot O3 - B4 stars in the Cyg OB2 association, including a high luminous star No. 12. Velocity fields in the atmospheres and interstellar medium, characteristics of optical spectra and line profiles are investigated. The cascade star formation scheme for the association is confirmed. Evidence is presented suggesting that the hypergiant Cyg OB2 No.12 is an LBV object and that its anomalous reddening has a circumstellar natu…
Three presumably young eclipsing binary systems in the direction of the Cygnus OB1, OB3 and OB9 associations are studied. Component spectra are reconstructed and their orbits are determined using light curves and spectra disentangling techniques. V443 Cyg and V456 Cyg have circular orbits, while the light curve of V2107\,Cyg imposes a slightly eccentric orbit ($e=0.045\pm0.03)$. V443 Cyg harbours F-type stars, and not young early-A stars as previously suggested in the literature based on photometry solely. It appears to be situated in the foreground (distance $0.6\pm0.2$ kpc) of the young stel…
Cyg OB2 is one of the most massive associations of O-type stars in our Galaxy. Despite the large interstellar reddening towards Cyg OB2, many studies, spanning a wide range of wavelengths, have been conducted to more clearly understand this association. X-ray observations provide a powerful tool to overcome the effect of interstellar absorption and study the most energetic processes associated with the stars in Cyg OB2. We analyse XMM-Newton data to investigate the X-ray and UV properties of massive O-type stars as well as low-mass pre-main sequence stars in Cyg OB2. We obtained six XMM-Newton…
In order to fully understand the gravitational collapse of molecular clouds, the star formation process and the evolution of circumstellar disks, these phenomena must be studied in different Galactic environments with a range of stellar contents and positions in the Galaxy. The young massive association Cygnus OB2, in the Cygnus-X region, is an unique target to study how star formation and the evolution of circumstellar disks proceed in the presence of a large number of massive stars. We present a catalog obtained with recent optical observations in r,i,z filters with OSIRIS, mounted on the $1…
The first Gaia Data Release presents an opportunity to characterise the low-mass population of OB associations, providing larger statistical samples and better constraints on the formation and evolution of clusters and associations. Using previously known low mass members in a small region of Vela OB2 we have designed selection criteria that combine Gaia and 2MASS photometry, independently of any astrometric information, to identify low-mass pre-main-sequence (PMS) stars over the wider association area. Our method picks out the known clusters of young stars around $γ^2$ Velorum and NGC-2547, b…
We present optical-infrared photometric and spectroscopic observations of Gaia18dvy, located in the Cygnus OB3 association at a distance of 1.88 kpc. The object was noted by the Gaia alerts system when its lightcurve exhibited a $\gtrsim$4 mag rise in 2018-2019. The brightening was also observable at mid-infared wavelengths. The infrared colors of Gaia18dvy became bluer as the outburst progressed. Its optical and near-infrared spectroscopic characteristics in the outburst phase are consistent with those of bona fide FU Orionis-type young eruptive stars. The progenitor of the outburst is probab…
Massive binary stars may constitute a substantial fraction of progenitors to supernovae and gamma-ray bursts, and the distribution of their orbital characteristics holds clues to the formation process of massive stars. As a contribution to securing statistics on OB-type binaries, we report the discovery and orbital parameters for five new systems as part of the Cygnus OB2 Radial Velocity Survey. Four of the new systems (MT070, MT174, MT267, and MT734 (a.k.a. VI Cygni #11) are single-lined spectroscopic binaries while one (MT103) is a double-lined system (B1V+B2V). MT070 is noteworthy as the lo…
In our Galaxy, star formation occurs in a variety of environments, with a large fraction of stars formed in clusters hosting massive stars. OB stars have an important feedback on the evolution of protoplanetary disks around nearby young stars and likely on the process of planet formation occurring in them. The nearby massive association Cygnus OB2 is an outstanding laboratory to study this feedback. It is the closest massive association to our Sun, and hosts hundreds of massive stars and thousands of low mass members. In this paper, we analyze the spatial variation of the disk fraction in Cygn…
We present the results of modeling of the spectrum of the brightest stars belonging to the Cyg OB2 association - #7 (O3If*) and #11 (O5Ifc). #7 is one of the hottest stars in our Galaxy, while #11 belongs to the spectral class Ofc, which was recently introduced and yet small in numbers (Walborn et al., 2010). We determine the physical properties and chemical composition of their atmosphere using CMFGEN code. The atmosphere of #7 reveals an excess of nitrogen X(N*)/X(Nsun) = 3.2 and the carbon and oxygen deficiency X(C*)/X(Csun) = 0.08, X(O*)/X(Osun) = 0.09, while the atmosphere of #11 is enric…
We present a catalog of photometrically variable stars discovered within two 21'.3 X 21'.3 fields centered on the Cygnus OB2 association. There have hitherto been no deep optical variability studies of Cyg OB2 despite it being replete with early-type massive stars, perhaps due to the high and variable extinction (up to A_V ~ 20) that permeates much of the region. Here we provide results of the first variability study with this combination of spatial coverage (~ 0.5 deg) and photometric depth (R ~ 21 mag). We find 121 stars to be variable in both R- and I-band, 116 of them newly discovered. Of …
We use Gaia DR2 data to survey the classic Monoceros OB1 region and look for the existence of a dispersed young population, co-moving with the cloud complex. An analysis of the distribution of proper motions reveals a 20-30 Myr association of young stars, about 300-400 pc away from the far side of the Mon OB1 complex, along the same general line-of-sight. We characterize the new association, Monoceros OB4, and estimate it contains between 1400 and 2500 stars, assuming a standard IMF, putting it on par in size with NGC\,2264. We find from the internal proper motions that Mon OB4 is unbound and …
We present the results of investigation of five stars, originally classified as dwarfs, belonging to Cyg OB2 association, their stellar and wind properties. Using both TLUSTY and CMFGEN codes we derived effective temperatures, surface gravities, chemical abundances, mass-loss rates and projected rotation velocities. Due to the fact that distance to the stars is well known, we were able to estimate their luminosities. Using evolutionary models we estimated the ages of these sample stars and find that lower mass ones - MT282 and MT343 - belong to older population of the association. Their ages a…
Historically, it has often been asserted that most stars form in compact clusters. In this scenario, present-day gravitationally-unbound OB associations are the result of the expansion of initially gravitationally-bound star clusters. However, this paradigm is inconsistent with recent results, both theoretical and observational, that instead favour a hierarchical picture of star formation in which stars are formed across a continuous distribution of gas densities and most OB associations never were bound clusters. Instead they are formed in-situ as the low-density side of this distribution, ra…
OB associations, birthplaces of the most luminous stars, are key objects for understanding the formation of high-mass stars and their effects on their environments. The aim of this work is to explore the structure and kinematics of the Cepheus OB2 association and characterize the history of star formation in the region -- in particular, the role of the Cepheus Bubble, surrounding Cepheus OB2. Based on \gaia\ DR3 data we study the spatial and age distribution and kinematics of young stars in the region. We select candidate pre-main-sequence stars in the $M_\mathrm{G}$ vs. \gbp$-$\grp\ colour-ma…
We present a search for stellar members of young associations within 150 pc of the Sun based on Gaia-Tycho and an updated version of the BANYAN $Σ$ software to determine Bayesian membership probabilities that includes Gaia-2MASS color-magnitude diagrams. We identify 32 new F0-M3-type bona fide members of the 10-200 Myr-old Sco-Cen, Carina, Tucana-Horologium, Columba and Octans associations and the AB Doradus, $β$ Pictoris and Carina-Near moving groups. These new bona fide members have measurements of their full kinematics and literature data consistent with a young age. We also confirm the mem…
Context. Establishing the multiplicity of O-type stars is the first step towards accurately determining their stellar parameters. Moreover, the distribution of the orbital parameters provides observational clues to the way that O-type stars form and to the interactions during their evolution. Aims. Our objective is to constrain the multiplicity of a sample of O-type stars belonging to poorly investigated OB associations in the Cygnus complex and for the first time to provide orbital parameters for binaries identified in our sample. Such information is relevant to addressing the issue of the bi…
We present a kinematic study of the Scorpius-Centaurus (Sco-Cen) OB association (Sco OB2) using Gaia DR1 parallaxes and proper motions. Our goal is to test the classical theory that OB associations are the expanded remnants of dense and compact star clusters disrupted by processes such as residual gas expulsion. Gaia astrometry is available for 258 out of 433 members of the association, with revised Hipparcos astrometry used for the remainder. We use this data to confirm that the three subgroups of Sco-Cen are gravitationally unbound and have non-isotropic velocity dispersions, suggesting they…
High-resolution spectra of the LBV candidate Schulte 12 in the Cyg OB2 association were obtained at the 6-meter BTA telescope with the NES echelle spectrograph on the arbitrary dates in 2001-2022. Variability of the emission profile of H$α$ and absorptions of HeI, SiII with time was found. Based on the radial velocity measurements at 10 observation dates, radial velocity variability with an amplitude of $Δ$Vr$\approx$8 km/s relative to the average value of the heliocentric velocity Vr=$-15.6\pm2.6$ km/s was revealed. This indicates the presence of a companion in the system. Based on the reliab…
We use new data from Gaia DR2 to confirm that the young L1 $γ$ candidate member of the TW Hya association (TWA) is now a bona fide member with a model-dependent mass estimate of ~15 $M_{Jup}$. The ambiguous M9 $γ$ candidate member 2MASS J12474428---3816464 also gets a higher Bayesian membership probability for TWA membership as a result of Gaia DR2 data and a new radial velocity measurement, but it remains unclear whether it is a true member of TWA or if it is an unrelated young interloper, because it is separated by 4.6 km/s from the locus of TWA members in UVW space.
Galactic Wolf-Rayet (WR) star membership of star forming regions can be used to constrain the formation environments of massive stars. Here, we utilise $\textit{Gaia}$ DR2 parallaxes and proper motions to reconsider WR star membership of clusters and associations in the Galactic disk, supplemented by recent near-IR studies of young massive clusters. We find that only 18$-$36% of 553 WR stars external to the Galactic Centre region are located in clusters, OB associations or obscured star-forming regions, such that at least 64% of the known disk WR population are isolated, in contrast with only …
In this paper we examine the nearest 100 pc entries in the data release 2 of Gaia to identify previously unrecognized candidate members in young associations. We analyze 695 952 stars with the BANYAN Σ Bayesian classification software and discover 898 new high-likelihood candidate members that span a wide range in properties, from spectral types B9 to L2, including 104 co-moving systems, 111 brown dwarfs and 31 new bona fide members. Our sample is mostly composed of highly active M dwarfs and will be crucial to examine the low-mass end of the initial mass function of young associations. Our sa…
Open clusters and associations are groups of young stars, respectively bound and unbound, that share the same origin and disperse over time into the galactic field. As such, their formation and evolution are the key to understand the origin and properties of galactic stellar populations. Moreover, since their members have about the same age, they are ideal laboratories to study the properties of young stars and constrain stellar evolution theories. In this contribution, I present our current knowledge on open clusters and associations. I focus on the methods used to derive the statistical prop…
I have used high-precision photometry and astrometry from the third data release of Gaia (DR3) to perform a survey for members of the Taurus star-forming region and young associations in its vicinity. This work has produced a new catalog of 532 adopted members of Taurus, which has only minor changes relative to the previous catalog from Esplin & Luhman 2019. I have used the Gaia astrometry to divide the Taurus members into 13 groups that have distinct kinematics. Meanwhile, I have identified 1378 candidate members of seven associations near Taurus. All of these associations have histograms of …
Stellar ages are key to improving our understanding of different astrophysical phenomena. However, many techniques to estimate stellar ages are highly model-dependent. The lithium depletion boundary (LDB), based on the presence or absence of lithium in low-mass stars, can be used to derive ages in stellar associations of between 20 and 500~Ma. The purpose of this work is to revise former LDB ages in stellar associations in a consistent way, taking advantage of the homogeneous \textit{Gaia} parallaxes as well as bolometric luminosity estimations that do not rely on monochromatic bolometric corr…
We have compiled a significantly updated and comprehensive census of massive stars in the nearby Cygnus OB2 association by gathering and homogenising data from across the literature. The census contains 169 primary OB stars, including 52 O-type stars and 3 Wolf-Rayet stars. Spectral types and photometry are used to place the stars in a Hertzprung-Russell diagram, which is compared to both non-rotating and rotating stellar evolution models, from which stellar masses and ages are calculated. The star formation history and mass function of the association are assessed, and both are found to be he…
It is often stated that star clusters are the fundamental units of star formation and that most (if not all) stars form in dense stellar clusters. In this monolithic formation scenario, low density OB associations are formed from the expansion of gravitationally bound clusters following gas expulsion due to stellar feedback. $N$-body simulations of this process show that OB associations formed this way retain signs of expansion and elevated radial anisotropy over tens of Myr. However, recent theoretical and observational studies suggest that star formation is a hierarchical process, following …
Using new proper motion data from recently published catalogs, we revisit the membership of previously identified members of the Upper Scorpius association. We confirmed 750 of them as cluster members based on the convergent point method, compute their kinematic parallaxes and combined them with Gaia parallaxes to investigate the 3D structure and geometry of the association using a robust covariance method. We find a mean distance of $146\pm 3\pm 6$~pc and show that the morphology of the association defined by the brightest (and most massive) stars yields a prolate ellipsoid with dimensions of…
Aims. Having established the binary status of nineteen O-type stars located in four Cygnus OB associations, we now determine their fundamental parameters to constrain their properties and their evolutionary status. We also investigate their surface nitrogen abundances, which we compare with other results from the literature obtained for galactic O-type stars. Methods. Using optical spectra collected for each object in our sample and some UV data from the archives, we apply the CMFGEN atmosphere code to determine their main properties. For the binary systems, we have disentangled the components…
We present results from a catalogue of 1696 X-ray point sources detected in the massive star forming region (SFR) Cygnus OB2, the majority of which have optical or near-IR associations. We derive ages of 3.5 and 5.25 Myrs for the stellar populations in our two fields, in agreement with recent studies that suggest that the central 1-3 Myr OB association is surrounded and contaminated by an older population with an age of 5-10 Myrs. The fraction of sources with proto-planetary disks, as traced by K-band excesses, are unusually low. Though this has previously been interpreted as due to the influe…
We have refined the census of stars and brown dwarfs in the Upper Sco association (~10 Myr, ~145 pc) by 1) updating the selection of candidate members from our previous survey to include the high-precision astrometry from the second data release of Gaia, 2) obtaining spectra of a few hundred candidate members to measure their spectral types and verify their youth, and 3) assessing the membership (largely with Gaia astrometry) of 2020 stars toward Upper Sco that show evidence of youth in this work and previous studies. We arrive at a catalog of 1761 objects that are adopted as members of Upper …
In the last decades, the early pre main sequence stellar rotational evolution picture has been constrained by studies targeting different young regions at a variety of ages. Observational studies suggest a mass-rotation dependence, and for some mass ranges a connection between rotation and the presence of a circumstellar disk. Not still fully explored, though, is the role of environmental conditions on the rotational regulation. We investigate the rotational properties of candidate members of the young massive association Cygnus OB2. The Stetson variability index, Lomb-Scargle periodogram, Sau…
Stellar kinematics provides the key to understanding star formation process. In this respect, we present a kinematic study of the Monoceros OB1 (Mon OB1) and R1 (Mon R1) associations using the recent Gaia data and radial velocities of stars derived from high-resolution spectroscopy and the literature. A total of 728 members are selected using the criteria based on the intrinsic properties of young stars, parallaxes, and proper motions. The spatial distribution and kinematic properties of members show that these associations have distinct substructures. In Mon OB1, we find one northern group an…
The Gaia mission has opened a new window into the internal kinematics of young star clusters at the sub-km/s level, with implications for our understanding of how star clusters form and evolve. We use a sample of 28 clusters and associations with ages from 1-5 Myr, where lists of members are available from previous X-ray, optical, and infrared studies. Proper motions from Gaia DR2 reveals that at least 75% of these systems are expanding; however, rotation is only detected in one system. Typical expansion velocities are on the order of ~0.5 km/s, and, in several systems, there is a positive rad…
In this research note we identify 130 new M-type candidate members of young associations with the BANYAN $Σ$ tool and recently published trigonometric distances from RECONS and URAT-South. We identify a white dwarf candidate in the AB Doradus moving group, but determine that its cooling age is too large and reject it as a member. Three stars (G 13-39, LHS 2935 and G 152-1) now have complete kinematics and are strong candidate members in the AB Doradus and Carina-Near moving groups, but still lack a confirmation of their young age independent of their kinematics.
We present the results of a J, H, and K photometric variability survey of the central 0.78 square degrees of the young OB association Cygnus OB2. We used data observed with the Wide-Field CAMera at the United Kingdom Infrared Telescope in 2007 (spanning 217 days) to investigate the light curves of 5083 low mass candidate members in the association and explore the occurrence and main characteristics of their near-infrared variability. We identified 2529 stars ($\sim$50$\%$ of the sample) with significant variability with time-scales ranging from days to months. We classified the variable stars …
I have used high-precision photometry and astrometry from the third data release of Gaia (DR3) to identify candidate members of the 32 Ori association. Spectral types and radial velocities have been measured for subsets of the candidates using new and archival spectra. For the candidates that have radial velocity measurements, I have used UVW velocities to further constrain their membership, arriving at a final catalog of 169 candidates. I estimate that the completeness of the survey is ~90% for spectral types of <=M7 (>=0.06 Msun). The histogram of spectral types for the 32 Ori candidates exh…
The proper motions (PMs) of OB stars in Cygnus have recently been found to exhibit two large-scale kinematic patterns suggestive of expansion. We perform a 3D traceback on these OB stars, the newly-identified OB associations and related open clusters in the region. We find that there are two groups of stars, associations and clusters and that they were each more compact in the past, reaching their closest approach $7.9^{+3.0}_{-1.8}$ and $8.5^{+0.8}_{-2.8}$ Myr ago. We consider two main scenarios for the driver of these large-scale expansion patterns: feedback-driven expansion from a previous …
We discuss the properties of H$α$ emission stars across the sample of 22035 spectra from the Gaia-ESO Survey internal data release, observed with the GIRAFFE instrument and largely belonging to stars in young open clusters. Automated fits using two independent Gaussian profiles and a third component that accounts for the nebular emission allow us to discern distinct morphological types of H$α$ line profiles with the introduction of a simplified classification scheme. All in all we find 3765 stars with intrinsic emission and sort their spectra into eight distinct morphological categories: singl…
Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS（巴黎天文台，巴黎文理研究大学，索邦大学，巴黎西岱大学，塞吉-蓬图瓦兹大学，法国国家科学研究中心）；Keele University（基尔大学）；University of Vienna, Department of Astrophysics（维也纳大学天体物理学系）；Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona（巴塞罗那大学宇宙科学研究所）；Kavli IPMU (WPI), UTIAS（开普勒行星系统物质宇宙学前沿中心（世界顶尖研究中心），东京大学宇宙线研究所）
利用盖亚卫星数据，通过 HDBSCAN 聚类算法在太阳附近 1 kpc 内识别出 56 个 OB 星协，数量翻倍，并对其物理和运动学特性进行了表征。
The evolutionary status of 24 post-AGB stars is presented based on Gaia DR3 data. All 24 stars have parallaxes accurate to better than 3 X sigma and have RUWE values less than 1.4. Based on the Gaia DR3 distances the absolute luminosities are derived. For 14 of the stars, the luminosities confirm their post-AGB evolutionary stage. However, V1027 Cyg, which was previously classified as a post-AGB star, is found to have a higher luminosity; thus it may be an evolved, massive, pulsating semi-regular variable star of type G7Ia. For 9 of the stars, the luminosities are lower than 1000 L (sun), indi…
Fundamental parameters and physical processes leading to the formation of white dwarfs (WDs) may be constrained and refined by discovering WDs in open clusters (OCs). Cluster membership can be utilized to establish the precise distances, luminosities, ages, and progenitor masses of such WDs. We compile a list of probable WDs that are OC members in order to facilitate WD studies that are impractical or difficult to conduct for Galactic field WDs. We use recent catalogs of WDs and OCs that are based on the second data release of the \textit{Gaia} satellite mission (GDR2) to identify WDs that are…
We present a catalogue of 1696 X-ray sources detected in the massive star forming region (SFR) Cygnus OB2 and extracted from two archival Chandra observations of the center of the region. A deep source extraction routine, exploiting the low background rates of Chandra observations was employed to maximize the number of sources extracted. Observations at other wavelengths were used to identify low count-rate sources and remove likely spurious sources. Monte Carlo simulations were also used to assess the authenticity of these sources. We used a Bayesian technique to identify optical or near-IR c…
The kinematic structure of the Cygnus OB2 association is investigated. No evidence of expansion or contraction is found at any scale within the region. Stars that are within $\sim$ 0.5 parsecs of one another are found to have more similar velocities than would be expected by random chance, and so it is concluded that velocity substructure exists on these scales. At larger scales velocity substructure is not found. We suggest that bound substructures exist on scales of $\sim$ 0.5 parsecs, despite the region as a whole being unbound. We further suggest that any velocity substructure that existed…
We search for runaway former companions of the progenitors of nearby Galactic core-collapse supernova remnants (SNRs) in the Tycho-Gaia astrometric solution (TGAS). We look for candidates for a sample of ten SNRs with distances less than $2\;\mathrm{kpc}$, taking astrometry and $G$ magnitude from TGAS and $B,V$ magnitudes from the AAVSO Photometric All-Sky Survey (APASS). A simple method of tracking back stars and finding the closest point to the SNR centre is shown to have several failings when ranking candidates. In particular, it neglects our expectation that massive stars preferentially ha…
The precise parallax, proper motion, and photometric measurements contained in Gaia Data Release 2 (DR2) offer the opportunity to re-examine the membership and ages of Nearby Young Moving Groups (NYMGs), i.e., loose groups of stars of age $\lesssim100$ Myr in the solar vicinity. Here, we analyze the available DR2 data for members and candidate members of the $ε$ Cha Association ($ε$CA) which, at an estimated age of $\sim$3--5 Myr, has previously been identified as among the youngest NYMGs. The several dozen confirmed members of $ε$CA include MP Mus and T Cha, two of the nearest stars of roughl…
This work provides a statistical analysis of the massive star binary characteristics in the Cygnus OB2 Association using radial velocity information of 114 B3-O3 primary stars and orbital properties for the 24 known binaries. We compare these data to a series of Monte Carlo simulations to infer the intrinsic binary fraction and distributions of mass ratios, periods, and eccentricities. We model the distribution of mass ratio, log-period, and eccentricity as power-laws and find best fitting indices of alpha=0.1+/-0.5, beta=0.2+/-0.4, and gamma=-0.6+/-0.3 respectively. These distributions indica…
High-contrast imaging studies of debris disks have revealed a significant diversity in their morphologies, including large-scale asymmetries. Theories involving stellar flybys, an external source of gravitational disturbance, have offered a plausible explanation for the origin of these morphological variations. Our study is an experiment to gain empirical evidence that has been lacking from such theories. We explore this paradigm by using astrometric and radial velocity measurements from the Gaia DR2 and ground-based observations to trace the trajectories of 625 stars in the Sco-Cen OB Associa…
This white paper proposes leveraging high-quality Gaia data available to the worldwide scientific community and complement it with support from Canadian-related facilities to place Canada as a leader in the fields of stellar associations and exoplanet science, and to train Canadian highly qualified personnel through graduate and post-graduate research grants. Gaia has sparked a new era in the study of stellar kinematics by measuring precise distances and proper motions for 1.3 billion stars. These data have already generated more than 1700 scientific papers and are guaranteed to remain the sou…
We investigate the spatial properties of sources from the GAIA catalogue previously identified as being members of the Taurus star forming region and which appear in the Spitzer catalogue. We study an area of sky of 10x15 deg, centred on Right Ascension (2000.0) = 68.5 deg and Declination (2000.0)= 27.0 deg, this being an area surrounding the Taurus molecular cloud. We use data obtained from the GAIA DR2 release. By using an inversion of GAIA parallax measurements to obtain distance values and by defining limits to the proper motions of the Taurus moving group, we are able to show that there a…
