scholarly journals Revisiting the case of R Monocerotis: Is CO removed at R < 20 au?

2018 ◽  
Vol 617 ◽  
pp. A31 ◽  
Author(s):  
T. Alonso-Albi ◽  
P. Riviere-Marichalar ◽  
A. Fuente ◽  
S. Pacheco-Vázquez ◽  
B. Montesinos ◽  
...  
Keyword(s):  
Spectral Type ◽  
Protoplanetary Disk ◽  
Emission Lines ◽  
Disk Model ◽  
Dispersal Mechanism ◽  
Disk Structure ◽  
Upper Limits ◽  
Intense Emission ◽  
Uv Photons ◽  
Continuum Data

Context. To our knowledge, R Mon is the only B0 star in which a gaseous Keplerian disk has been detected. However, there is some controversy about the spectral type of R Mon. Some authors propose that it could be a later B8e star, where disks are more common. Aims. Our goal is to re-evaluate the R Mon spectral type and characterize its protoplanetary disk. Methods. The spectral type of R Mon has been re-evaluated using the available continuum data and UVES emission lines. We used a power-law disk model to fit previous 12CO 1 →0 and 2 →1 interferometric observations and the PACS CO data to investigate the disk structure. Interferometric detections of 13CO J = 1 →0, HCO+ 1 →0, and CN 1 →0 lines using the IRAM Plateau de Bure Interferometer (PdBI) are presented. The HCN 1 →0 line was not detected. Results. Our analysis confirms that R Mon is a B0 star. The disk model compatible with the 12CO 1 →0 and 2 →1 interferometric observations falls short of predicting the observed fluxes of the 14 < Ju < 31 PACS lines; this is consistent with the scenario in which some contribution to these lines is coming from a warm envelope and/or UV-illuminated outflow walls. More interestingly, the upper limits to the fluxes of the Ju > 31 CO lines suggest the existence of a region empty of CO at R ≲ 20 au in the protoplanetary disk. The intense emission of the HCO+ and CN lines shows the strong influence of UV photons on gas chemistry. Conclusions. The observations gathered in this paper are consistent with the presence of a transition disk with a cavity of Rin ≳ 20 au around R Mon. This size is similar to the photoevaporation radius that supports the interpretation that UV photoevaporation is main disk dispersal mechanism in massive stars

scholarly journals Upper limits on CH3OH in the HD 163296 protoplanetary disk

2019 ◽  
Vol 623 ◽  
pp. A124 ◽  
Author(s):  
M. T. Carney ◽  
M. R. Hogerheijde ◽  
V. V. Guzmán ◽  
C. Walsh ◽  
K. I. Öberg ◽  
...  
Keyword(s):  
Gas Phase ◽  
Column Density ◽  
Matched Filter ◽  
Image Plane ◽  
Protoplanetary Disk ◽  
Chemical Complexity ◽  
Disk Structure ◽  
T Tauri ◽  
Upper Limits ◽  
Integrated Intensity

Context. Methanol (CH3OH) is at the root of organic ice chemistry in protoplanetary disks. Its connection to prebiotic chemistry and its role in the chemical environment of the disk midplane make it an important target for disk chemistry studies. However, its weak emission has made detections difficult. To date, gas-phase CH3OH is detected in only one Class II disk, TW Hya. Aims. We aim to constrain the methanol content of the HD 163296 protoplanetary disk. Methods. We used the Atacama Large Millimeter/submillimeter Array (ALMA) to search for a total of four CH3OH emission lines in bands six and seven toward the disk around the young Herbig Ae star HD 163296. The disk-averaged column density of methanol and its related species formaldehyde (H2CO) were estimated assuming optically thin emission in local thermodynamic equilibrium. We compared these results to the gas-phase column densities of the TW Hya disk. Results. No targeted methanol lines were detected with Keplerian masking in the image plane nor with matched filter analysis in the uv plane individually nor after line stacking. The 3σ disk-integrated intensity upper limits are <51 mJy km s−1 for the band six lines and <26 mJy km s−1 for the band seven lines. The band seven lines provide the strictest 3σ upper limit on disk-averaged column density with Navg < 5.0 × 1011 cm−2. The methanol-to-formaldehyde ratio is CH3OH∕H2CO<0.24 in the HD 163296 disk compared to a ratio of 1.27 in the TW Hya disk. Conclusions. The HD 163296 protoplanetary disk is less abundant in methanol with respect to formaldehyde compared to the disk around TW Hya. Differences in the stellar irradiation in this Herbig Ae disk as compared to that of a disk around a T Tauri star likely influence the gaseous methanol and formaldehyde content. Possible reasons for the lower HD 163296 methanol-to-formaldehyde ratio include: a higher than expected gas-phase formation of H2CO in the HD 163296 disk, uncertainties in the grain surface formation efficiency of CH3OH and H2CO, and differences in the disk structure and/or CH3OH and H2CO desorption processes that drive the release of the molecules from ice mantles back into the gas phase. These results provide observational evidence that the gas-phase chemical complexity found in disks may be strongly influenced by the spectral type of the host star.

scholarly journals Using HCO+ isotopologues as tracers of gas depletion in protoplanetary disk gaps

2020 ◽  
Vol 644 ◽  
pp. A4
Author(s):  
Grigorii V. Smirnov-Pinchukov ◽  
Dmitry A. Semenov ◽  
Vitaly V. Akimkin ◽  
Thomas Henning
Keyword(s):  
Line Emission ◽  
Physical Structure ◽  
Protoplanetary Disk ◽  
Line Ratio ◽  
X Rays ◽  
Disk Model ◽  
Moment Maps ◽  
Disk Structure ◽  
Molecular Abundances ◽  
Far Ultraviolet

Context. The widespread rings and gaps seen in the dust continuum in protoplanetary disks are sometimes accompanied by similar substructures seen in molecular line emission. One example is the outer gap at ~100 au in AS 209, which shows that the H13CO+ and C18O emission intensities decrease along with the continuum in the gap, while the DCO+ emission increases inside the gap. Aims. We aim to study the behavior of DCO+/H13CO+ and DCO+/HCO+ ratios in protoplanetary disk gaps assuming the two scenarios: (A) the gas depletion follows the dust depletion and (B) only the dust is depleted. Methods. We first modeled the physical disk structure using the thermo-chemical model ANDES. This 1+1D steady-state disk model calculates the thermal balance of gas and dust and includes the far ultraviolet, X-rays, cosmic rays, and other ionization sources together with the reduced chemical network for molecular coolants. Afterward, this physical structure was adopted for calculations of molecular abundances with the extended gas-grain chemical network with deuterium fractionation. Ideal synthetic spectra and 0th-moment maps were produced with the LIne Modeling Engine. Results. We are able to qualitatively reproduce the increase in the DCO+ intensity and the decrease in the H13CO+ and C18O intensities inside the disk gap, which is qualitatively similar to what is observed in the outer AS 209 gap. The corresponding disk model (A) assumes that both the gas and dust are depleted in the gap. The model (B) with the gas-rich gap, where only the dust is depleted, produces emission that is too bright in all HCO+ isotopologues and C18O. Conclusions. The DCO+/H13CO+ line ratio can be used to probe gas depletion in dust continuum gaps outside of the CO snow line. The DCO+/C18O line ratio shows a similar, albeit weaker, effect; however, these species can be observed simultaneously with a single (sub)mm interferometer setup.

scholarly journals Interacting Binaries as Be Stars

1987 ◽  
Vol 92 ◽  
pp. 451-455
Author(s):  
Mirek J. Plavec
Keyword(s):  
Spectral Type ◽  
Binary Stars ◽  
Emission Lines ◽  
Close Binary ◽  
High Electron ◽  
Be Stars ◽  
Close Binary Stars ◽  
High Ionization ◽  
Mass Outflow ◽  
Balmer Lines

AbstractSemidetached close binary stars of the Algol type often have primary components of spectral type A0 or earlier and display emission at Hα (sometimes also at higher Balmer lines). They are therefore Be stars. Many binaries of this type are not eclipsing and must look like “ordinary” Be stars. We have discovered high-ionization emission lines of N V, C IV, Si IV, Fe III, etc. in the ultraviolet spectra of totally eclipsing Algols. They probably originate in circumstellar turbulent regions at fairly high electron temperatures, of the order of 100 000 K. They are not detectable in most non-eclipsing systems, but may be there and may play an important role in the dynamics of accretion and mass outflow from the systems.

scholarly journals A new possible accretion scenario for ultra-luminous X-ray sources

2019 ◽  
Vol 489 (1) ◽  
pp. 366-384 ◽  
Author(s):  
Shogo B Kobayashi ◽  
K Nakazawa ◽  
K Makishima
Keyword(s):  
Emission Lines ◽  
Emission Model ◽  
Massive Black Holes ◽  
X Ray ◽  
Local Structures ◽  
Upper Limits ◽  
Nearby Galaxies ◽  
Model Independent ◽  
Spectral States ◽  
Spectral State

ABSTRACT Using archival data from Suzaku, XMM–Newton, and NuSTAR, nine representative ultra-luminous X-ray sources (ULXs) in nearby galaxies were studied. Their X-ray spectra were all reproduced with a multicolour disc emission model plus its Comptonization. However, the spectral shapes of individual sources changed systematically depending on the luminosity, and defined three typical spectral states. These states differ either in the ratio between the Comptonizing electron temperature and the innermost disc temperature, or in the product of Compton y-parameter and fraction of the Comptonized disc photons. The luminosity range at which a particular state emerges was found to scatter by a factor of up to 16 among the eight ULXs. By further assuming that the spectral state is uniquely determined by the Eddington ratio, the sample ULXs are inferred to exhibit a similar scatter in their masses. This gives a model-independent support to the interpretation of ULXs in terms of relatively massive black holes. None of the spectra showed noticeable local structures. Especially, no Fe K-shell absorption/emission lines were detected, with upper limits of 30–40 eV in equivalent width from the brightest three among the sample: NGC 1313 X-1, Holmberg IX X-1, and IC 342 X-1. These properties disfavour ordinary mass accretion from a massive companion star, and suggest direct Bondi–Hoyle accretion from dense parts of the interstellar medium.

scholarly journals MWC 314 – A new galactic B[e] supergiant

1994 ◽  
Vol 162 ◽  
pp. 396-397
Author(s):  
Anatoly S. Miroshnichenko
Keyword(s):  
Radio Source ◽  
Spectral Type ◽  
Emission Lines ◽  
Spectral Features ◽  
Late Type ◽  
Symbiotic System ◽  
Strong Emission ◽  
Normal Star ◽  
Late Type Star ◽  
Gaseous Envelope

We present a new study of MWC 314 = BD +14°3887 – a poorly investigated object with strong emission lines and IR excesses. Merrill (1927) payed attention to it because of the presence of hydrogen and Fe II emissions in its spectrum. Swensson (1942) also detected interstellar lines H and K CaII and 4430 Å band, Balmer emissions from Hα to H8, NaI 5890 and 5896 Å emissions and estimated its spectral type as gG2-3 or dG4-5 from the SED in continuum, and B2 from the excitation degree. Photospheric lines and spectral features of late-type stars were not observed. Allen (1973) noted that the object's SED corresponds to that of a late-type star but it might be a symbiotic system or a reddened normal star. The IRAS fluxes were obtained only at 12 and 25 μm. The object is unknown as a radio source. From this we can conclude that this system consists of, at least, a hot star surrounded by a gaseous envelope.

A step further on the physical, kinematic and excitation properties of PNe

2018 ◽  
Vol 14 (S343) ◽  
pp. 409-410
Author(s):  
Denise Rocha Gonçalves ◽  
Stavros Akras
Keyword(s):  
Central Star ◽  
The Other ◽  
Emission Lines ◽  
Formation Processes ◽  
Excitation Mechanism ◽  
Electron Densities ◽  
Chemical Abundances ◽  
Shock Models ◽  
Intense Emission

AbstractPNe are known to be photoionized objects. However they also have low-ionization structures (LIS) with different excitation behavior. We are only now starting to answer why most LIS have lower electron densities than the PN shells hosting them, and whether or not their intense emission in low-ionization lines is the key to their main excitation mechanism. Can LIS line ratios, chemical abundances and kinematics enlight the interplay between the different excitation and formation processes in PNe? Based on the spectra of five PNe with LIS and using new diagnostic diagrams from shock models, we demonstrate that LIS’s main excitation is due to shocks, whereas the other components are mainly photoionized. We propose new diagnostic diagrams involving a few emission lines ([N II], [O III], [S II]) and fshocks/f*, where fshocks and f* are the ionization photon fluxes due to the shocks and to the central star ionizing continuum, respectively.

scholarly journals Eruptive Phenomena as a Source of the Observed Variations of Intrinsic Polarization in Long Period and T Tau Variables

1983 ◽  
Vol 71 ◽  
pp. 515-518
Author(s):  
M. Sole ◽  
G. Strazzulla
Keyword(s):  
Temperature Dependence ◽  
Equivalent Width ◽  
Emission Lines ◽  
Rapid Rise ◽  
Intrinsic Polarization ◽  
Colour Centres ◽  
Long Period ◽  
Uv Photons ◽  
T Tau

ABSTRACTThe correlation between the rapid rise of intrinsic polarization, increasing U-B and enhanced equivalent width of Balmer, H and K emission lines is interpreted as a consequence of the activation of colour centres in circumstellar silicate dust by X/UV photons from flares. The temperature dependence of bleaching is discussed and the number of centres producing polarization changes is estimated.

Chromospheric activity in red giants, and related phenomena

1970 ◽  
Vol 36 ◽  
pp. 199-208
Author(s):  
Armin J. Deutsch
Keyword(s):  
Emission Line ◽  
Spectral Type ◽  
Time Scale ◽  
Vacuum Ultraviolet ◽  
Time Variable ◽  
Emission Lines ◽  
Absorption Lines ◽  
Red Giants ◽  
Chromospheric Activity ◽  
Near Ultraviolet

Normal red giants of a given spectral type are shown to be heterogeneous with respect to the following chromospheric features: the Balmer absorption lines, the emission line at H∊, and the double-reversed emission lines at Caii H and K. These chromospheric lines are also shown to be strongly time variable, in at least some red giants, on a time scale of a few months or years. Other chromospheric features that require study lie in the infrared (Hei 10830), the near ultraviolet (Feii emission lines), and the vacuum ultraviolet.

scholarly journals NLTE-Analysis of Three Extremely Helium-Rich O-Type Subdwarfs

1985 ◽  
Vol 87 ◽  
pp. 353-357
Author(s):  
C. Husfeld ◽  
U. Heber ◽  
J.S. Drilling
Keyword(s):  
Spectral Type ◽  
White Dwarf ◽  
Asymptotic Giant Branch ◽  
Evolutionary Status ◽  
Type B ◽  
Hot Stars ◽  
Upper Limits ◽  
Helium Stars ◽  
Effective Temperatures

AbstractThree extremely helium-rich sdO stars (LSE 153, LSE 259 and LSE 263) were analyzed spectroscopically by means of detailed NLTE model atmospheres. These stars are very hot, with effective temperatures ranging from 70000 to 75000 K and gravities between log g = 4.4 and 4.9. Upper limits for the hydrogen abundance were also derived. The evolutionary status of the sdO stars is discussed and it is concluded that they evolve from the asymptotic giant branch towards the white dwarf stage. A possible evolutionary link between these hot stars and the extreme helium stars of spectral type B is discussed.

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