- 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.
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- 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.
- ID:
- ivo://CDS.VizieR/J/AJ/151/75
- Title:
- Herschel-PACS and -SPIRE spectroscopy of 70 objects
- Short Name:
- J/AJ/151/75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the COPS-DIGIT-FOOSH (CDF) Herschel spectroscopy data product archive, and related ancillary data products, along with data fidelity assessments, and a user-created archive in collaboration with the Herschel-PACS and SPIRE ICC groups. Our products include datacubes, contour maps, automated line fitting results, and best 1D spectra products for all protostellar and disk sources observed with PACS in RangeScan mode for two observing programs: the DIGIT Open Time Key Program (KPOT\_nevans\_1 and SDP\_nevans\_1; PI: N. Evans), and the FOOSH Open Time Program (OT1\_jgreen02\_2; PI: J. Green). In addition, we provide our best SPIRE-FTS spectroscopic products for the COPS Open Time Program (OT2\_jgreen02\_6; PI: J. Green) and FOOSH sources. We include details of data processing, descriptions of output products, and tests of their reliability for user applications. We identify the parts of the data set to be used with caution. The resulting absolute flux calibration has improved in almost all cases. Compared to previous reductions, the resulting rotational temperatures and numbers of CO molecules have changed substantially in some sources. On average, however, the rotational temperatures have not changed substantially (<2%), but the number of warm (T_rot_~300K) CO molecules has increased by about 18%.
- ID:
- ivo://CDS.VizieR/J/A+A/565/A109
- Title:
- Herschel/PACS spectra of 48 evolved stars
- Short Name:
- J/A+A/565/A109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 48 Herschel/PACS spectra of evolved stars in the wavelength range of 67-72um. This wavelength range covers the 69mu band of crystalline olivine (Mg_2-2x_Fe_(2x)_SiO_4_). The width and wavelength position of this band are sensitive to the temperature and composition of the crystalline olivine. Our sample covers a wide range of objects: from high mass-loss rate AGB stars (OH/IR stars, dM/dt>=10^-5^M_{sun}_/yr), through post-AGB stars with and without circumbinary disks, to planetary nebulae and even a few massive evolved stars. The goal of this study is to exploit the spectral properties of the 69um band to determine the composition and temperature of the crystalline olivine. Since the objects cover a range of evolutionary phases, we study the physical and chemical properties in this range of physical environments. We fit the 69um band and use its width and position to probe the composition and temperature of the crystalline olivine. For 27 sources in the sample, we detected the 69um band of crystalline olivine (Mg_2-2x_Fe_(2x)_SiO_4_). The 69um band shows that all the sources produce pure forsterite grains containing no iron in their lattice structure. The temperature of the crystalline olivine as indicated by the 69um band, shows that on average the temperature of the crystalline olivine is highest in the group of OH/IR stars and the post-AGB stars with confirmed Keplerian disks. The temperature is lower for the other post-AGB stars and lowest for the planetary nebulae. A couple of the detected 69um bands are broader than those of pure magnesium-rich crystalline olivine, which we show can be due to a temperature gradient in the circumstellar environment of these stars. The disk sources in our sample with crystalline olivine are very diverse. They show either no 69um band, a moderately strong band, or a very strong band, together with a temperature for the crystalline olivine in their disk that is either very warm (~600K), moderately warm (~200K), or cold (~120K), respectively.
- ID:
- ivo://CDS.VizieR/J/ApJ/841/116
- Title:
- Herschel spectra of 11 very low mass stars
- Short Name:
- J/ApJ/841/116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The properties of disks around brown dwarfs and very low mass stars (hereafter VLMOs) provide important boundary conditions on the process of planet formation and inform us about the numbers and masses of planets than can form in this regime. We use the Herschel Space Observatory PACS spectrometer to measure the continuum and [OI]63{mu}m line emission toward 11 VLMOs with known disks in the Taurus and Chamaeleon I star-forming regions. We fit radiative transfer models to the spectral energy distributions of these sources. Additionally, we carry out a grid of radiative transfer models run in a regime that connects the luminosity of our sources with brighter T Tauri stars. We find that VLMO disks with sizes 1.3-78au, smaller than typical T Tauri disks, fit well the spectral energy distributions assuming that disk geometry and dust properties are stellar mass independent. Reducing the disk size increases the disk temperature, and we show that VLMOs do not follow previously derived disk temperature-stellar luminosity relationships if the disk outer radius scales with stellar mass. Only 2 out of 11 sources are detected in [OI] despite a better sensitivity than was achieved for T Tauri stars, suggesting that VLMO disks are underluminous. Using thermochemical models, we show that smaller disks can lead to the unexpected [OI]63{mu}m nondetections in our sample. The disk outer radius is an important factor in determining the gas and dust observables.
