- ID:
- ivo://CDS.VizieR/J/A+A/567/A15
- Title:
- Hen 2-260 emission line fluxes
- Short Name:
- J/A+A/567/A15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analysed the planetary nebula Hen 2-260 using optical spectroscopy and photometry. We compared our observations with the literature data in order to search for evolutionary changes. We also searched for photometric variability of the central star. Hen 2-260 was observed with the SAAO 1.0m telescope (photometry) and the SALT telescope (low resolution spectroscopy). We also used archive high resolution Very Large Telescope spectra and Hubble Space Telescope imaging. The nebular line fluxes were modelled with the Cloudy photoionization code in order to derive the stellar and nebular parameters. The planetary nebula shows a complex structure and possibly a bipolar outflow. The nebula is relatively dense and young. The central star is just starting O^+^ ionization (Teff~30000K). Comparison of our observations with literature data indicates a 50% increase of the [OIII] 5007{AA} line flux between 2001 and 2012. We interpret it as the result of the progression of the ionization of O^+^. The central star evolves to higher temperatures at a rate of 45+/-7K/yr. The heating rate is consistent with post-AGB evolutionary tracks for a final mass of 0.626^+0.003^_-0.005_M_{sun}_ or 0.645+/-0.008M_{sun}_ for two different sets of tracks from literature. The photometric monitoring of Hen 2-260 revealed non-periodic variations on a timescale of hours or days. There is no direct indication for central star binarity in the spectrum, nor for a strong stellar wind. The variability may be caused by pulsations of the star. The temperature evolution of the central star can be traced using spectroscopic observations of the surrounding planetary nebula spanning a timescale of roughly a decade. This allows us for precise determination of the stellar mass, since the pace of the temperature evolution depends critically on the core mass. The method is independent on the absolute age of the nebula. The kinematical age of the nebula is consistent with the age obtained from the evolutionary track. The final mass of the central star is close to the peak of the mass distribution for central stars of planetary nebulae found in other studies. The object belongs to a group of young central stars of planetary nebulae showing photometric variability.
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- ID:
- ivo://CDS.VizieR/J/MNRAS/453/976
- Title:
- Herbig Ae/Be X-shooter observations
- Short Name:
- J/MNRAS/453/976
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Herbig Ae/Be stars (HAeBes) span a key mass range that links low- and high-mass stars, and thus provide an ideal window from which to explore their formation. This paper presents Very Large Telescope/X-shooter spectra of 91 HAeBes, the largest spectroscopic study of HAeBe accretion to date. A homogeneous approach to determining stellar parameters is undertaken for the majority of the sample. Measurements of the ultraviolet are modelled within the context of magnetospheric accretion, allowing a direct determination of mass accretion rates. Multiple correlations are observed across the sample between accretion and stellar properties: the youngest and often most massive stars are the strongest accretors, and there is an almost 1:1 relationship between the accretion luminosity and stellar luminosity. Despite these overall trends of increased accretion rates in HAeBes when compared to classical T Tauri stars, we also find noticeable differences in correlations when considering the Herbig Ae and Herbig Be subsets. This, combined with the difficulty in applying a magnetospheric accretion model to some of the Herbig Be stars, could suggest that another form of accretion may be occurring within Herbig Be mass range.
- ID:
- ivo://CDS.VizieR/J/A+A/439/129
- Title:
- HERES II. Spectroscopic analysis
- Short Name:
- J/A+A/439/129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of analysis of "snapshot" spectra of 253 metal-poor halo stars -3.8<=[Fe/H]<=-1.5 obtained in the HERES survey. The snapshot spectra have been obtained with VLT/UVES and have typically S/N~54 per pixel (ranging from 17 to 308), R~20000, lambda=3760-4980{AA}. This sample represents the major part of the complete HERES sample of 373 stars; however, the CH strong content of the sample is not dealt with here.
- ID:
- ivo://CDS.VizieR/J/A+A/650/L17
- Title:
- HERMES spectra of Betelgeuse
- Short Name:
- J/A+A/650/L17
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Despite being the best studied red supergiant star in our Galaxy, the physics behind the photometric variability and mass loss of Betelgeuse is poorly understood. Moreover, recently the star has experienced an unusual fading with its visual magnitude reaching a historical minimum. The nature of this event was investigated by several studies where mechanisms like episodic mass loss and presence of dark spots in the photosphere were invoked. We aim at relating the atmospheric dynamics of Betelgeuse to its photometric variability, with the main focus on the dimming event. We use the tomographic method which allows us to probe different depths in the stellar atmosphere and to recover the corresponding disk-averaged velocity field. The method is applied to a series of high-resolution HERMES observations of Betelgeuse. Variations in the velocity field are then compared with photometric and spectroscopic variations. The tomographic method reveals that the succession of two shocks along our line-of-sight (in February 2018 and January 2019), the second one amplifying the effect of the first one, combined with underlying convection or/and outward motion present at this phase of the 400 d pulsation cycle, produced a rapid expansion of a portion of the atmosphere of Betelgeuse and an outflow between October 2019 and February 2020. This resulted in a sudden increase of molecular opacity in the cooler upper atmosphere of Betelgeuse and, thus, in the observed unusual decrease of the star's brightness.
1015. HERMES spectra of IP Eri
- ID:
- ivo://CDS.VizieR/J/A+A/567/A30
- Title:
- HERMES spectra of IP Eri
- Short Name:
- J/A+A/567/A30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We determine the orbital elements for the K0 IV + white dwarf (WD) system IP Eri, which appears to have a surprisingly long period of 1071d and a significant eccentricity of 0.25. Previous spectroscopic analyses of the WD, based on a distance of 101pc inferred from its Hipparcos parallax, yielded a mass of only 0.43M_{sun}_, implying it to be a helium-core WD. The orbital properties of IP~Eri are similar to those of the newly discovered long-period subdwarf B star (sdB) binaries, which involve stars with He-burning cores surrounded by extremely thin H envelopes, and are therefore close relatives to He WDs. We performed a spectroscopic analysis of high-resolution spectra from the HERMES/Mercator spectrograph and concluded that the atmospheric parameters of the K0 component are Teff=4960K, logg=3.3, [Fe/H]=0.09 and vt=1.5km/s. The detailed abundance analysis focuses on C, N, O abundances, carbon isotopic ratio, light (Na, Mg, Al, Si, Ca, Ti) and s-process (Sr, Y, Zr, Ba, La, Ce, Nd) elements. We conclude that IP~Eri abundances agree with those of normal field stars of the same metallicity. The long period and non-null eccentricity indicate that this system cannot be the end product of a common-envelope phase; it calls instead for another less catastrophic binary-evolution channel presented in detail in a companion paper.
- ID:
- ivo://CDS.VizieR/J/A+A/639/L6
- Title:
- HERMES spectra of LS V +22 25
- Short Name:
- J/A+A/639/L6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The intriguing binary LS V +22 25 (LB-1) has drawn much attention following claims of it being a single-lined spectroscopic binary with a 79-day orbit comprising a B-type star and a ~70M_{sun}_ black hole - the most massive stellar black hole reported to date. Subsequent studies demonstrated a lack of evidence for a companion of such great mass. Recent analyses have implied that the primary star is a stripped He-rich star with peculiar sub-solar abundances of heavy elements, such as Mg and Fe. However, the nature of the secondary, which was proposed to be a black hole, a neutron star, or a main sequence star, remains unknown. Based on 26 newly acquired spectroscopic observations secured with the HERMES and FEROS spectrographs covering the orbit of the system, we perform an orbital analysis and spectral disentangling of LB-1 to elucidate the nature of the system. To derive the radial velocity semi-amplitude K2 of the secondary and extract the spectra of the two components, we used two independent disentangling methods: the shift-and-add technique and Fourier disentangling with FDBinary. We used atmosphere models to constrain the surface properties and abundances. Our disentangling and spectral analysis shows that LB-1 contains two components of comparable brightness in the optical. The narrow-lined primary, which we estimate to contribute 55% in the optical, has spectral properties that suggest that it is a stripped star: it has a small spectroscopic mass (~1M_{sun}_) for a B-type star and it is He- and N-rich. Unlike previous reports, the abundances of heavy elements are found to be solar. The 'hidden' secondary, which contributes about 45% of the optical flux, is a rapidly rotating (vsini~300km/s) B3 V star with a decretion disk - a Be star. As a result of its rapid rotation and dilution, the photospheric absorption lines of the secondary are not readily apparent in the individual observations.We measure a semi-amplitude for this star of K2=11.2+/-1.0km/s and adopting a mass of M2=72M_{sun}_ typical for B3 V stars, we derive an orbital mass for the stripped primary of M1=1.5+/-0.4 M_{sun}_. The orbital inclination of 394 implies a near-critical rotation for the Be secondary (v_eq_~470km/s). LB-1 does not contain a compact object. Instead, it is a rare Be binary system consisting of a stripped star (the former mass donor) and a Be star rotating at near its critical velocity (the former mass accretor). This system is a clear example that binary interactions play a decisive role in the production of rapid stellar rotators and Be stars.
- ID:
- ivo://CDS.VizieR/J/A+A/626/A23
- Title:
- Herschel Dwarf Galaxy Survey PACS spectroscopy
- Short Name:
- J/A+A/626/A23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We employ a multiphase approach to model the ISM phases of the galaxies from the Herschel Dwarf Galaxy Survey with the spectral synthesis code Cloudy. We characterize the physical conditions (gas densities, radiation fields, porosity) in those galaxies and investigate correlations with metallicity or star-formation activity. We find that the lower-metallicity galaxies tend to have higher ionization parameters and galaxies with higher specific star-formation rates have higher gas densities. The [CII] emission arises mainly from PDRs and the contribution from the ionized gas phases is small, typically less than 30% of the observed emission. We also find a correlation, with scatter, between metallicity and both the PDR covering factor and the fraction of [CII] from the ionized gas. Overall, the low metal abundances appear to be driving most of the changes in the ISM structure and conditions of these galaxies, and not the high specific star-formation rates. These results demonstrate in a quantitative way the increase of ISM porosity at low metallicity.
- ID:
- ivo://CDS.VizieR/J/ApJ/846/32
- Title:
- Herschel FIR spectra of GOALS galaxies
- Short Name:
- J/ApJ/846/32
- Date:
- 13 Dec 2021 06:52:25
- Publisher:
- CDS
- Description:
- We present an analysis of [OI]_63_, [OIII]_88_, [NII]_122_, and [CII]_158_ far-infrared (FIR) fine-structure line observations obtained with Herschel/PACS, for ~240 local luminous infrared galaxies (LIRGs) in the Great Observatories All-sky LIRG Survey. We find pronounced declines ("deficits") of line-to-FIR continuum emission for [NII]_122_, [OI]_63_, and [CII]_158_ as a function of FIR color and infrared luminosity surface density, {Sigma}_IR_. The median electron density of the ionized gas in LIRGs, based on the [NII]_122_/[NII]_205_ ratio, is n_e_=41cm^-3^. We find that the dispersion in the [CII]_158_ deficit of LIRGs is attributed to a varying fractional contribution of photodissociation regions (PDRs) to the observed [CII]_158_ emission, f([CII]_158_^PDR^)=[CII]_158_^PDR^/[CII]_158_, which increases from ~60% to ~95% in the warmest LIRGs. The [OI]_63_/[CII]_158_^PDR^ ratio is tightly correlated with the PDR gas kinetic temperature in sources where [OI]_63_ is not optically thick or self-absorbed. For each galaxy, we derive the average PDR hydrogen density, n_H_, and intensity of the interstellar radiation field, G, in units of G_0_ and find G/n_H_ ratios of ~0.1-50G_0_.cm^3^, with ULIRGs populating the upper end of the distribution. There is a relation between G/n_H_ and {Sigma}_IR_, showing a critical break at {Sigma}_IR_^*^~5x10^10^L_{sun}_/kpc^2^. Below {Sigma}_IR_^*^, G/n_H_ remains constant, ~0.32G_0_.cm^3^, and variations in {Sigma}_IR_ are driven by the number density of star-forming regions within a galaxy, with no change in their PDR properties. Above {Sigma}_IR_^*^, G/n_H_ increases rapidly with {Sigma}_IR_, signaling a departure from the typical PDR conditions found in normal star-forming galaxies toward more intense/harder radiation fields and compact geometries typical of starbursting sources.
- ID:
- ivo://CDS.VizieR/J/ApJ/814/133
- Title:
- Herschel Galactic plane survey of [NII]
- Short Name:
- J/ApJ/814/133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first large-scale high angular resolution survey of ionized nitrogen in the Galactic Plane through emission of its two fine structure transitions ([N II]) at 122 and 205 {mu}m. The observations were largely obtained with the PACS instrument onboard the Herschel Space Observatory. The lines of sight were in the Galactic plane, following those of the Herschel OTKP project GOT C+. Both lines are reliably detected at the 10^-8^-10^-7^ W/m^2^/sr level over the range -60{deg}<=l<=60{deg}. The rms of the intensity among the 25 PACS spaxels of a given pointing is typically less than one third of the mean intensity, showing that the emission is extended. [N II] is produced in gas in which hydrogen is ionized, and collisional excitation is by electrons. The ratio of the two fine structure transitions provides a direct measurement of the electron density, yielding n(e) largely in the range 10-50 cm^-3^ with an average value of 29 cm^-3^ and N^+^ column densities 10^16^-10^17^ cm^-2^. [N II] emission is highly correlated with that of [C II], and we calculate that between 1/3 and 1/2 of the [C II] emission is associated with the ionized gas. The relatively high electron densities indicate that the source of the [N II] emission is not the warm ionized medium (WIM), which has electron densities more than 100 times smaller. Possible origins of the observed [N II] include the ionized surfaces of dense atomic and molecular clouds, the extended low-density envelopes of H II regions, and low-filling factor high-density fluctuations of the WIM.
- ID:
- ivo://CDS.VizieR/J/A+A/542/A76
- Title:
- Herschel-HIFI water spectra of W43-MM1
- Short Name:
- J/A+A/542/A76
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Herschel/HIFI observations of 14 water lines in W43-MM1, a massive protostellar object in the luminous star-cluster-forming region W43. We place our study in the more general context of high-mass star formation. The dynamics of these regions may be represented by either the monolithic collapse of a turbulent core, or competitive accretion. Water turns out to be a particularly good tracer of the structure and kinematics of the inner regions, allowing an improved description of the physical structure of the massive protostar W43-MM1 and an estimation of the amount of water around it. We analyze the gas dynamics from the line profiles using Herschel-HIFI observations acquired as part of the Water In Star-forming regions with Herschel project of 14 far-IR water lines (H_2_^16^O, H_2_^17^O, H_2_^18^O), CS(11-10), and C^18^O(9-8) lines, using our modeling of the continuum spectral energy distribution. The spectral modeling tools allow us to estimate outflow, infall, and turbulent velocities and molecular abundances. We compare our results to previous studies of low-, intermediate-, and other high-mass objects. As for lower-mass protostellar objects, the molecular line profiles are a mix of emission and absorption, and can be decomposed into 'medium' (full width at half maximum FWHM~=5-10km/s), and 'broad' velocity components (FWHM~=20-35km/s). The broad component is the outflow associated with protostars of all masses. Our modeling shows that the remainder of the water profiles can be well-fitted by an infalling and passively heated envelope, with highly supersonic turbulence varying from 2.2km/s in the inner region to 3.5km/s in the outer envelope. In addition, W43-MM1 has a high accretion rate of between 4.0x10^-4^ and 4.0x10^-2^M_{sun}_/yr, as derived from the fast (0.4-2.9km/s) infall observed. We estimate a lower mass limit for gaseous water of 0.11M_{sun}_ and total water luminosity of 1.5L_{sun}_ (in the 14 lines presented here). The central hot core is detected with a water abundance of 1.4x10^-4^, while the water abundance for the outer envelope is 8x10^-8^. The latter value is higher than in other sources, and most likely related to the high turbulence and the micro-shocks created by its dissipation. Examining the water lines of various energies, we find that the turbulent velocity increases with the distance from the center. While not in clear disagreement with the competitive accretion scenario, this behavior is predicted by the turbulent core model. Moreover, the estimated accretion rate is high enough to overcome the expected radiation pressure.
