446494 research outputs found
Sort by
Infrared photometry and calcium triplet spectroscopy of the most metal-poor in situ globular cluster VVV-CL001
No full textContext. The characterization of globular clusters (GCs) in the Galactic bulge is a challenging task due to high extinction and severe stellar crowding. VVV-CL001 is a poorly studied GC located in the inner bulge, known for its extremely old age, extreme velocity, and low metallicity. Given its unique properties, a detailed study of this cluster can provide valuable insights into the early chemical and dynamical evolution of the Milky Way (MW).
Aims. The aim of this study was to derive the fundamental parameters of VVV-CL001 including metallicity, heliocentric radial velocity (RV), proper motions (PMs), structural properties, orbit, and age, in order to improve our understanding of its origin and role in the early evolution of the MW.
Methods. We combined spectroscopic, astrometric, and photometric data to characterize VVV-CL001. Metallicity and RV were determined from medium-resolution spectra obtained with FORS2 at the Very Large Telescope. PMs were derived using Gaia DR3 data. Near-infrared photometry from the FourStar instrument on Magellan was used to refine the cluster’s position, construct a radial density profile, and estimate its age, distance, and reddening.
Results. Our results confirm that VVV-CL001 is an old 12.1−1.2+1.0 Gyr), metal-poor ([Fe/H] = −2.25 ± 0.05 dex) globular cluster located at a heliocentric position of d⊙ = 7.1−1.1+1.3, with a reddening of E(J − Ks) = 1.40−0.02+0.01. Its mean PMs are μα* = −3.68 ± 0.09 mas yr−1 and µδ = −1.76 ± 0.10 mas yr−1, and it exhibits a RV of −334 ± 4 km s−1. The cluster follows a retrograde-prograde eccentric (e = 0.76−0.14+0.10) orbit, confined within the Galactic plane (|Z|max = 1.0−0.32+0.45 kpc) and inside the bar’s radius of influence (R < 5 kpc), with a pericenter of rperi = 0.6−0.2+0.3 kpc and an apocenter of rapo = 4.5−1.2+2.5 kpc.
Conclusions. These orbital properties, combined with its ancient age and low metallicity, strongly support an in situ origin for VVV-CL001 and likely membership of the disk GC system that was captured by the potential of the bar during its formation. Thus, VVV-CL001 emerges as a fossil remnant of the earliest phases of Galactic assembly and a valuable tracer of the population that contributed to the formation of the inner thick disk and bulge, which are likely part of the main progenitor of the MW. Our study highlights the relevance of detailed chemo-dynamical analyses in unveiling the origin of GCs in the inner Galaxy
A vertically orientated dark matter halo marks a flip of the Galactic disc
No full textUnveiling the 3D shape of the Milky Way’s dark-matter halo is critical to understanding its formation history. We created an innovative dynamical model that makes minimal assumptions about the internal dynamical structures and accommodates a highly flexible triaxial DM halo. By applying the method to 6D phase-space data of K-giant stars from LAMOST + Gaia, we robustly determined the 3D dark-matter distribution of the Milky Way out to approximately 50 kpc. We discovered a triaxial, nearly oblate dark-matter halo with qDM = Z/X = 0.92 ± 0.08, pDM = Y/X = 0.8 ± 0.2 on average within 50 kpc, where the Z-axis is defined perpendicular to the stellar disc. The axes ratio qDM > pDM is strongly preferred; the long-intermediate axis plane of the dark-matter halo is unexpectedly vertical to the Galactic disc, yet aligned with the ‘plane of satellites’. This striking configuration suggests that the Galactic disc (and the inner halo) has flipped, likely torqued by minor mergers, from an original alignment with the outer dark-matter halo and satellite plane, as is supported by Milky Way analogues from Auriga and TNG50. By allowing qDM(r) and pDM(r) to vary with radii, we find tentative evidence that the dark-matter halo is twisted. This agrees alignment with the disc in the inner regions and transitions to a vertical orientation at r > 20 kpc, supporting the disc flip scenario prediction. Such disc reorientation is non-trivial, yet its physical mechanism is straightforward to comprehend and naturally originates a vertical satellite plane. Our findings offer a unified framework that links dark-matter halo orientation, satellite alignment, and disc evolution, reinforcing the internal consistency of the Milky Way in the Λ cold dark matter model
The stellar activity-rotation-age relationship under the lens of asteroseismology
No full textContext. In low-mass stars, the connection between magnetic activity, rotation period, and age provides key insights into the functioning of dynamos. Fully understanding the activity-rotation-age relationship requires access to stars with precise fundamental parameters, measured rotation periods, and reliable magnetic activity indicators (e.g. X-ray luminosity). Thanks to space-based photometry, asteroseismology is now the leading method for determining stellar parameters with unprecedented precision and accuracy. The best-characterised solar-like stars compose the Kepler LEGACY sample, with the highest quality asteroseismic data for 66 stars, most of which have measured rotation periods. In the X-ray band, these stars were observed by the ROentgen Survey with an Imaging Telescope Array (eROSITA) telescope on the Russian Spektrum-Roentgen-Gamma (SRG) satellite in the course of its all-sky survey.
Aims. We reviewed different components of the stellar activity–rotation–age relationship using the largest sample of solar-like stars with highly accurate fundamental parameters from asteroseismology, along with their measured rotation periods and X-ray luminosities.
Methods. We cross-correlated the Kepler LEGACY sample with the SRG/eROSITA source catalogue, finding X-ray detections for 13 of them. We derived their fundamental parameters using the Forward and Inversion COmbination (FICO) procedure and revisited widely studied activity-age and activity-rotation relationships by consistently incorporating our subsample of 13 stars with literature samples.
Results. By implementing revised activity-rotation-age relationships in a star-planet interaction (SPI) code to compute the X-ray luminosity tracks and by comparing the results with observations, we found an improved agreement for seven stars of our subsample. We explored the effect of the revised relationships on the mass loss of planets in the radius valley, finding a modest impact on planet size distributions.
Conclusions. A larger and more varied sample of stars with asteroseismically characterised parameters, rotation period, and activity indicators is needed to accurately determine the multiple components of the activity-rotation-age relationship
A spectral-line survey of CIT 6 between 30 and 50 GHz with the eQ receiver at NRO 45 m
No full textContext. At the end of the long H-burning phase (main sequence), low-mass to intermediate-mass stars evolve into asymptotic giant branch (AGB) stars that can have carbon-rich envelopes depending on the initial C/O ratio. In their circumstellar envelopes (CSEs), dust particles and molecules are formed and shed back to the interstellar space. Therefore, these stars significantly contribute to the galactic astro-chemical evolution.
Aims. To shed light on the chemical properties of carbon-rich CSEs, especially carbon- and silicon-bearing molecules, we performed parallel spectral-line surveys of IRC+10216 and CIT 6, the brightest and second-brightest carbon-rich star envelopes on the sky.
Methods. We conducted 30−50 GHz observations towards both sources using a high-sensitivity-wide-band extended Q-band receiver (eQ) of the Nobeyama 45−m telescope. We then analysed data of CIT 6 and used data of IRC+10216 for comparison purposes. We applied the rotational-diagram method to derive their rotational temperatures and column densities for HC5N and HC7N. For other molecules, we assumed an excitation temperature to derive their column densities.
Results. Molecular column densities in CIT 6 are systematically lower than those of IRC+10216, typically by one order of magnitude. Silicon- and sulfur-bearing species such as SiS and CS show the strongest depletion, whereas carbon-chain molecules (HCnN, C6H) remain relatively prominent, indicating that carbon-chain formation is still efficient in CIT 6. Rotational temperatures are higher in CIT 6, which is consistent with the fact that emission arises from warmer and more compact regions of its envelope. Both sources show low 12C/13C ratios and mildly sub-solar 28Si/29Si values, which are non-solar isotopic ratios.
Conclusions. Both envelopes display canonical, carbon-rich AGB chemistry and comparable isotopic compositions. CIT 6, however, shows slightly higher excitation temperatures, stronger carbon-chain growth, and deeper depletion of Si- and S-bearing species. These signatures point to a more evolved circumstellar environment, where dust condensation and shock processing further modulated the molecular composition
A solar jet-induced perturbation propagating through coronal loops and in-loop electron beam transport as indicated by type II and type N radio bursts
No full textAims. Solar type II radio bursts are commonly attributed to coronal shocks driven by coronal mass ejections (CMEs). However, some metric type II bursts have occasionally been reported to occur in the absence of a CME and to be associated with weak solar activity. The aim of this study is to identify the driver of the coronal shock in this kind of type II event.
Methods. We investigated a high-frequency metric type II burst with clear band splitting, observed simultaneously by the Chashan Broadband Solar radio spectrograph and the Nançay Radioheliograph. It is associated with a C3.1-class flare and a small-scale jet, but without a detectable CME in the coronagraphs.
Results. The type II burst is preceded by multiple type III bursts, one of which exhibits characteristics of a type N burst. The type II burst source is associated with the jet-induced perturbation front propagating through nearby closed loops at a speed of ∼880 km s−1, rather than the much slower jet front. This suggests that the disturbance initiated by the jet can convert to a shock wave within low Alfvénic coronal loops, providing the necessary conditions for electron acceleration and subsequent radio emission. Our findings offer new insights into the formation mechanism of high-frequency type II bursts associated with weak flares and jets
A global view on star formation: The GLOSTAR Galactic plane survey
No full textContext. Extended radio continuum emission and its linear polarization play a key role in probing large-scale structures of synchrotron and free-free emission in the Milky Way. Despite the existence of many radio continuum surveys, sensitive, high-angular-resolution single-dish surveys of extended radio continuum emission remain scarce.
Aims. Our objective is to deliver a Galactic plane survey of extended radio continuum emission within the 4–8 GHz frequency range, achieving an unprecedented angular resolution of ≲3′. As part of the GLObal view of STAR formation (GLOSTAR) survey, we also crucially complement existing data from the Karl G. Jansky Very Large Array (VLA) by addressing the missing zero-spacing gap.
Methods. Within the framework of the GLOSTAR Galactic plane survey, we performed large-scale radio continuum imaging observations toward the Galactic plane in the range −2° < ℓ < 60° and |b| < 1.1°, as well as the Cygnus X region (76° < ℓ < 83° and −1° < b < 2°) with the Effelsberg 100-m Radio Telescope.
Results. We present the Effelsberg continuum survey at 4.89 GHz and 6.82 GHz, including linear polarization, with angular resolutions of 145′′ and 106′′, respectively. The survey has been corrected for missing large-scale emission using available low-angular-resolution surveys. Comparison with previous single-dish surveys indicates that our continuum survey represents the highest-quality single-dish data collected to date at this frequency. More than 90% of the flux density missed by the VLA D-array data is effectively recovered by the Effelsberg continuum survey. The improved sensitivity and angular resolution of our survey enable reliable mapping of Galactic magnetic field structures, with polarization data less affected by depolarization than in previous surveys. The GLOSTAR single-dish continuum data will be released publicly, offering a valuable resource for studying extended objects including HI
The SRG/eROSITA all-sky survey: Hard X-ray selected active galactic nuclei
No full textContext. The eROSITA instrument on board the Spectrum Roentgen Gamma (SRG) satellite performed its first all-sky survey between December 2019 and June 2020. This paper presents the resulting hard X-ray (2.3–5 keV) sample, the first created from an all-sky imaging survey in this energy range, for sources within the western galactic sky (eROSITA-DE).
Aims. We produced a large uniform sample of hard-X-ray selected active galactic nuclei (AGN), and characterised them with supporting multi-wavelength astrometry, photometry, and spectroscopy. For the 2863 sources within the sky coverage of the DESI imaging Legacy Survey Data Release 10 (LS10; >15 000 deg2), counterparts were identified and classified. We also performed comparisons with the Swift BAT sample and HEAO-1 AGN sample to attempt to better understand the effectiveness and sensitivity of eROSITA in the hard band.
Methods. The 5466 hard X-ray selected sources detected with eROSITA are presented and discussed here. The Bayesian statistics-based code NWA
ExoplaNeT accRetion mOnitoring sPectroscopic surveY (ENTROPY)
No full textContext. Accretion processes in the planetary-mass regime are still poorly constrained, yet they strongly impact the formation and evolution of planets and the composition of circumplanetary disks.
Aims. We investigate the resolved Balmer hydrogen emission-line profiles and their variability timescales in the ∼13 MJup, 30−45 Myr-old companion Delorme 1 (AB)b to derive constraints on the accretion mechanism at play.
Methods. With VLT/UVES, we collected 31 new epochs of high-resolution optical (330–680 nm) spectra of the companion at R = 50 000, probing variability on timescales of hours to years. We study the companion’s H
Photometric variability of nitrogen-rich Wolf-Rayet stars in Magellanic Clouds with OGLE
No full textAims. We present a comprehensive analysis of the photometric variability of (presumably single) nitrogen-rich Wolf-Rayet (WN) stars in the Magellanic Clouds, using long-term observations from the OGLE survey.
Methods. Our sample comprises 47 stars with no nearby Gaia counterparts. We characterize both overall and short-term variabilities, examining data dispersion and identifying periodicities. To validate our findings, we also compare the OGLE light curves with data from the MACHO and TESS missions.
Results. Variability is ubiquitous in our WR sample: about one third of stars display high variability, or four fifths if we include cases with moderate variations. The observed changes are found to be periodic in 11 cases, with timescales of 2–56 d. Such periodic variations originate in corotating wind structures, binary effects, or pulsations, thereby increasing the number of systems known to show these phenomena. Surprisingly, nine targets display (quasi-periodic) outbursts, making such changes a new type of WR variability. The variability shows a transient character, in about 30% of the sample, with changing amplitudes for periodic signals or for outbursts (they even sometimes completely disappear from view). Finally, we identified six long-period variables, four of which have been confirmed by at least two independent surveys