Miroslaw Schmidt - Academia.edu (original) (raw)

Papers by Miroslaw Schmidt

Author Institution: Sackler Laboratory for Astrophysics, Leiden Observatory, University of Leiden... more Author Institution: Sackler Laboratory for Astrophysics, Leiden Observatory, University of Leiden, P.O. Box 9513, NL-2300 RA Leiden, the Netherlands; LaserLaB, VU University Amsterdam, De Boelelaan 1081, NL-1081 HV, Amsterdam, The Netherlands; Department of Astrophysics, N. Copernicus Astronomical Center; ul. Rabianska 8, 87-100 Torun, Poland; Centre for Astronomy, Nicolaus Copernicus University, Gagarina 11, 87-100 Torun, Poland; Instituto de Astronomia, Universidad Catolica del Norte, Av. Angamos 0610; Antofagasta, Chile

Monthly Notices of the Royal Astronomical Society, 2001

The paper presents a survey of profiles of reasonably strong diffuse interstellar bands (DIBs) ba... more The paper presents a survey of profiles of reasonably strong diffuse interstellar bands (DIBs) based on the extensive set of high-resolution spectra acquired with the aid of echelle spectrographs installed at the 2-m Terskol, 2-m Pic du Midi and 1-m SAO telescopes. The surveyed diffuse interstellar bands cover the spectral ranges of blue and near-infrared, i.e the DIBs not surveyed by Kreøowski & Schmidt. The possible modifications caused by stellar and telluric lines are discussed. The very broad features such as 4430 are not discussed because the shapes of their profiles, extracted from echelle spectra, are very uncertain. The signal-to-noise (S/N) ratios of the spectra are not high enough to enable discussion of the profiles of numerous weak interstellar features discovered recently.

Monthly Notices of the Royal Astronomical Society, 2013

We report observations of four weak absorption lines of the interstellar CN A 2 −X 2 + (3,0) band... more We report observations of four weak absorption lines of the interstellar CN A 2 −X 2 + (3,0) band: R 1 (0) 6951.8 Å, R Q 21 (0) 6927.3 Å, R 2 (1)+ R Q 1 (1) 6926.7 Å, Q R 12 (1)+Q 1 (1) 6953.6 Å, and show that they provide reasonable information on column densities in sightlines towards early-type stars. The (3,0) band is always very weak and thus the saturation effect is negligible, which is particularly useful for the sightlines where the near UV-range CN bands are very strong, i.e. saturated.

Astronomy & Astrophysics, 2013

Context. Observations of the circumstellar envelopes of post-asymptotic giant branch (post-AGB) s... more Context. Observations of the circumstellar envelopes of post-asymptotic giant branch (post-AGB) stars provide information about their mass-loss history during the AGB phase and about the chemistry inside envelopes after that phase. Aims. We analyze visual observations of C 2 molecule in absorption and millimeter and sub-millimeter observations of CO molecule in emission with the aim of determining the physical and chemical conditions in the circumstellar shell of the carbon-rich post-AGB star IRAS 22272+5435. Methods. We determined the column densities and excitation structure of C 2 from equivalent width analysis of the molecular absorptions. The thermal and density structure of post-AGB shell (AGB remnant) is constrained by multilevel radiative transfer modeling of CO emission lines. The chemical structure of the envelope was computed and then used in the multilevel radiative transfer in C 2 for comparison with observed column densities. Results. We estimate the column density of C 2 to be 3.2 × 10 15 cm −2. From the chemical model we estimate peak abundance of C 2 as 6.8 × 10 −6 relative to nucleon density. The absorption of molecular lines originate in the ring between 5 and 10 × 10 16 cm. The excitation temperature of the lowest levels of 58 K is consistent with the gas kinetic temperature derived from the CO modeling. The initial abundance of the parent molecule C 2 H 2 inferred from the analysis is found to be 1.27 × 10 −5 relative to nucleon density. Conclusions. C 2 molecule is a promising tool for probing the temperature structure of the envelopes of post-AGB objects and indirectly for determining the chemical abundance of acetylene.

The statistical investigations of a large sample of F, G and K field stars by Cayrel de Strobel &... more The statistical investigations of a large sample of F, G and K field stars by Cayrel de Strobel & Bentolila (1983, A&A, 119) indicate many apparent chemical anomalies among these stars, particularly those of low gravity. The physical properties, i.e. effective temperatures and surface gravities, as well as elemental abundances and microturbulent velocities of two K4-type giants, namely HD 14872 (65 And) and HD 209960 (20 Cep), are determined, both by a differential curve of growth method relative to α Boo and by synthetic spectrum analysis

Reports on Mathematical Physics, 1994

The concept'of bifurcation belongs to one of Poincart's pioneering studies. In 1885, Poincare int... more The concept'of bifurcation belongs to one of Poincart's pioneering studies. In 1885, Poincare introduced the notion of bifurcation, discussed the elements of the theory and described the phenomenon to an extremely detailed extent. The basic elements of the theory may be grouped into three areas: critical solutions, dynamic stability and structural stability. Our work concerns the area of structural stability, namely we use the topological degree theory methods to get local and global bifurcation results.

We report the results of a sensitive search for the minor isotopologues of water, H2-17O and H2-1... more We report the results of a sensitive search for the minor isotopologues of water, H2-17O and H2-18O, toward the carbon-rich AGB star IRC+10216 (a.k.a. CW Leonis) using the HIFI instrument on the Herschel Space Observatory. This search was motivated by the fact that any detection of isotopic enhancement in the H2-17O and H2-18O abundances would have strongly implicated CO photodissociation as the source of the atomic oxygen needed to produce water in a carbon-rich circumstellar envelope. Our observations place an upper limit of 1/470 on the H2-17O/H2-16O abundance ratio. Given the isotopic 17O/16O ratio of 1/840 inferred previously for the photosphere of IRC+10216, this result places an upper limit of a factor 1.8 on the extent of any isotope-selective enhancement of H2-17O in the circumstellar material, and provides an important constraint on any model that invokes CO photodissociation as the source of O for H2O production. In the context of the clumpy photodissociation model proposed previously for the origin of water in IRC+10216, our limit implies that 12C-16O (not 13C-16O or SiO) must be the dominant source of 16O for H2O production, and that the effects of self-shielding can only have reduced the 12C-16O photodissociation rate by at most a factor ~ 2.

The Astrophysical Journal Letters, Jan 3, 2011

We report the results of observations of ten rotational transitions of water vapor toward the car... more We report the results of observations of ten rotational transitions of water vapor toward the carbonrich AGB (asymptotic giant branch) star IRC+10216 (CW Leonis), carried out with Herschel's HIFI instrument. Each transition was securely detected by means of observations using the dual beam switch mode of HIFI. The measured line ratios imply that water vapor is present in the inner outflow at small distances (≤ few × 10 14 cm) from the star, confirming recent results reported by Decin et al. from observations with Herschel's PACS and SPIRE instruments. This finding definitively rules out the hypothesis that the observed water results from the vaporization of small icy objects in circular orbits. The origin of water within the dense C-rich envelope of IRC+10216 remains poorly understood. We derive upper limits on the H 17 2 O/H 16 2 O and H 18 2 O/H 16 2 O isotopic abundance ratios of ∼ 5 × 10 −3 (3 σ), providing additional constraints on models for the origin of the water vapor in IRC+10216.

We present optical and infrared spectroscopy of V1309 Sco, an object that erupted in 2008 in a st... more We present optical and infrared spectroscopy of V1309 Sco, an object that erupted in 2008 in a stellar-merger event. During the outburst, V1309 Sco displayed characteristics typical of red transients, a class of objects similar to V838 Mon. Our observations were obtained in 2009 and 2012, i.e. months and years after the eruption of V1309 Sco, and illustrate severe changes in the remnant, mainly in its circumstellar surroundings. In addition to atomic gas observed in earlier epochs, we identified molecular bands of TiO, VO, H 2 O, ScO, AlO, and CrO. The infrared bands of CrO we analyse are the first astronomical identification of the features. Over the whole period covered by our data, the remnant was associated with a cool ( 1000 K) outflow with a terminal velocity of about 200 km s −1 . Signatures of warmer atomic gas, likely to be still dissipating the energy of the 2008 outburst, dramatically decreased their brightness between 2009 and 2012. In addition, the source of optical continuum disappeared sometime before 2012, likely owing to the formation of new dust. The final stage of V1309 Sco's evolution captured by our spectra is an object remarkably similar to an older red transient, V4332 Sgr. In addition to providing a detailed view on the settling of the eruptive object, the observations presented here reinforce the conclusion that all the Galactic red transients are a manifestation of the same phenomenon, i.e. a stellar merger. The late spectra of V1309 Sco also suggest peculiarities in the chemical composition of the remnant, which still need to be explored.

Astronomy & Astrophysics, 2015

We present optical and infrared spectroscopy of V1309 Sco, an object which erupted in 2008 in a s... more We present optical and infrared spectroscopy of V1309 Sco, an object which erupted in 2008 in a stellar-merger event. During the outburst, V1309 Sco displayed characteristics typical for red transients, a class of objects similar to V838 Mon. Our observations were obtained in 2009 and 2012, i.e. months and years after the eruption of V1309 Sco, and illustrate severe changes in the remnant, mainly in its circumstellar surroundings. In addition to atomic gas observed in earlier epochs, we identified molecular bands of TiO, VO, H 2 O, ScO, AlO, and CrO. Infrared bands of CrO we analyze are first astronomical identification of those features. Over the whole period covered by our data, the remnant was associated with a cool ( 1000 K) outflow with a terminal velocity of about 200 km s −1 . Signatures of warmer atomic gas, likely to be still dissipating the energy of the 2008 outburst, dramatically decreased their brightness between 2009 and 2012. Also, sometime before 2012 the source of optical continuum disappeared, likely owing to formation of new dust. The final stage captured by our spectra show an object remarkably similar to an older red transient, V4332 Sgr. In addition to providing a detailed view on the settling of the eruptive object, the observations presented here reinforce the conclusion that all the Galactic red transients are a manifestation of the same phenomenon, i.e. a stellar merger. Also, the late spectra of V1309 Sco suggest pecularities in the chemical composition of the remnant, which yet need to be explored.

We report the results of observations of ten rotational transitions of water vapor toward the car... more We report the results of observations of ten rotational transitions of water vapor toward the carbon-rich AGB (asymptotic giant branch) star IRC+10216 (CW Leonis), carried out with Herschel's HIFI instrument. Each transition was securely detected by means of observations using the dual beam switch mode of HIFI. The measured line ratios imply that water vapor is present in the inner outflow at small distances (few x 1.E+14 cm) from the star, confirming recent results reported by Decin et al. from observations with Herschel's PACS and SPIRE instruments. This finding definitively rules out the hypothesis that the observed water results from the vaporization of small icy objects in circular orbits. The origin of water within the dense C-rich envelope of IRC+10216 remains poorly understood. We derive upper limits on the H2-17O/H2-16O and H2-18O/H2-16O isotopic abundance ratios of ~ 5.E-3 (3 sigma), providing additional constraints on models for the origin of the water vapor in IR...

ESO Astrophysics Symposia, 1998

ESO Astrophysics Symposia, 1998

ESO Astrophysics Symposia, 1998

Proceedings of the International Astronomical Union, 2008

We present high-resolution and high signal-to-noise spectroscopic observations of interstellar mo... more We present high-resolution and high signal-to-noise spectroscopic observations of interstellar molecular lines of C2 towards early-type stars. C2 is particularly interesting because it is the simplest multicarbon molecule and its abundances give information on the chemistry of interstellar clouds, especially on the pathway of formation of (hydro)carbon chains and PAHs which may be considered as possible carriers of diffuse interstellar bands (DIBs). Homonuclear diatomic molecules have negligible dipol moments and hence radiative cooling of excited rotational levels may go only trough the slow quadrupole transitions (van Dishoeck & Black 1982). In C2, pumped by galactic average interstellar field rotational levels are excited effectively much above the gas kinetic temperature and a rotational ladder of electronic transitions is usually observed from high rotational levels. Relations between abundances of the dicarbon and other simple interstellar molecules are considered as well.

The Astrophysical Journal, 2011

We report the results of observations of ten rotational transitions of water vapor toward the car... more We report the results of observations of ten rotational transitions of water vapor toward the carbonrich AGB (asymptotic giant branch) star IRC+10216 (CW Leonis), carried out with Herschel's HIFI instrument. Each transition was securely detected by means of observations using the dual beam switch mode of HIFI. The measured line ratios imply that water vapor is present in the inner outflow at small distances (≤ few × 10 14 cm) from the star, confirming recent results reported by Decin et al. from observations with Herschel's PACS and SPIRE instruments. This finding definitively rules out the hypothesis that the observed water results from the vaporization of small icy objects in circular orbits. The origin of water within the dense C-rich envelope of IRC+10216 remains poorly understood. We derive upper limits on the H 17 2 O/H 16 2 O and H 18 2 O/H 16 2 O isotopic abundance ratios of ∼ 5 × 10 −3 (3 σ), providing additional constraints on models for the origin of the water vapor in IRC+10216.

The Astrophysical Journal, 2013

We report the results of a sensitive search for the minor isotopologues of water, H 17 2 O and H ... more We report the results of a sensitive search for the minor isotopologues of water, H 17 2 O and H 18 2 O, toward the carbon-rich AGB star IRC+10216 (a.k.a. CW Leonis) using the HIFI instrument on the Herschel Space Observatory. This search was motivated by the fact that any detection of isotopic enhancement in the H 17 2 O and H 18 2 O abundances would have strongly implicated CO photodissociation as the source of the atomic oxygen needed to produce water in a carbon-rich circumstellar envelope. Our observations place an upper limit of 1/470 on the H 17 2 O/H 16 2 O abundance ratio. Given the isotopic 17 O/ 16 O ratio of 1/840 inferred previously for the photosphere of IRC+10216, this result places an upper limit * Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA

Author Institution: Sackler Laboratory for Astrophysics, Leiden Observatory, University of Leiden... more Author Institution: Sackler Laboratory for Astrophysics, Leiden Observatory, University of Leiden, P.O. Box 9513, NL-2300 RA Leiden, the Netherlands; LaserLaB, VU University Amsterdam, De Boelelaan 1081, NL-1081 HV, Amsterdam, The Netherlands; Department of Astrophysics, N. Copernicus Astronomical Center; ul. Rabianska 8, 87-100 Torun, Poland; Centre for Astronomy, Nicolaus Copernicus University, Gagarina 11, 87-100 Torun, Poland; Instituto de Astronomia, Universidad Catolica del Norte, Av. Angamos 0610; Antofagasta, Chile

Monthly Notices of the Royal Astronomical Society, 2001

The paper presents a survey of profiles of reasonably strong diffuse interstellar bands (DIBs) ba... more The paper presents a survey of profiles of reasonably strong diffuse interstellar bands (DIBs) based on the extensive set of high-resolution spectra acquired with the aid of echelle spectrographs installed at the 2-m Terskol, 2-m Pic du Midi and 1-m SAO telescopes. The surveyed diffuse interstellar bands cover the spectral ranges of blue and near-infrared, i.e the DIBs not surveyed by Kreøowski & Schmidt. The possible modifications caused by stellar and telluric lines are discussed. The very broad features such as 4430 are not discussed because the shapes of their profiles, extracted from echelle spectra, are very uncertain. The signal-to-noise (S/N) ratios of the spectra are not high enough to enable discussion of the profiles of numerous weak interstellar features discovered recently.

Monthly Notices of the Royal Astronomical Society, 2013

We report observations of four weak absorption lines of the interstellar CN A 2 −X 2 + (3,0) band... more We report observations of four weak absorption lines of the interstellar CN A 2 −X 2 + (3,0) band: R 1 (0) 6951.8 Å, R Q 21 (0) 6927.3 Å, R 2 (1)+ R Q 1 (1) 6926.7 Å, Q R 12 (1)+Q 1 (1) 6953.6 Å, and show that they provide reasonable information on column densities in sightlines towards early-type stars. The (3,0) band is always very weak and thus the saturation effect is negligible, which is particularly useful for the sightlines where the near UV-range CN bands are very strong, i.e. saturated.

Astronomy & Astrophysics, 2013

Context. Observations of the circumstellar envelopes of post-asymptotic giant branch (post-AGB) s... more Context. Observations of the circumstellar envelopes of post-asymptotic giant branch (post-AGB) stars provide information about their mass-loss history during the AGB phase and about the chemistry inside envelopes after that phase. Aims. We analyze visual observations of C 2 molecule in absorption and millimeter and sub-millimeter observations of CO molecule in emission with the aim of determining the physical and chemical conditions in the circumstellar shell of the carbon-rich post-AGB star IRAS 22272+5435. Methods. We determined the column densities and excitation structure of C 2 from equivalent width analysis of the molecular absorptions. The thermal and density structure of post-AGB shell (AGB remnant) is constrained by multilevel radiative transfer modeling of CO emission lines. The chemical structure of the envelope was computed and then used in the multilevel radiative transfer in C 2 for comparison with observed column densities. Results. We estimate the column density of C 2 to be 3.2 × 10 15 cm −2. From the chemical model we estimate peak abundance of C 2 as 6.8 × 10 −6 relative to nucleon density. The absorption of molecular lines originate in the ring between 5 and 10 × 10 16 cm. The excitation temperature of the lowest levels of 58 K is consistent with the gas kinetic temperature derived from the CO modeling. The initial abundance of the parent molecule C 2 H 2 inferred from the analysis is found to be 1.27 × 10 −5 relative to nucleon density. Conclusions. C 2 molecule is a promising tool for probing the temperature structure of the envelopes of post-AGB objects and indirectly for determining the chemical abundance of acetylene.

The statistical investigations of a large sample of F, G and K field stars by Cayrel de Strobel &... more The statistical investigations of a large sample of F, G and K field stars by Cayrel de Strobel & Bentolila (1983, A&A, 119) indicate many apparent chemical anomalies among these stars, particularly those of low gravity. The physical properties, i.e. effective temperatures and surface gravities, as well as elemental abundances and microturbulent velocities of two K4-type giants, namely HD 14872 (65 And) and HD 209960 (20 Cep), are determined, both by a differential curve of growth method relative to α Boo and by synthetic spectrum analysis

Reports on Mathematical Physics, 1994

The concept'of bifurcation belongs to one of Poincart's pioneering studies. In 1885, Poincare int... more The concept'of bifurcation belongs to one of Poincart's pioneering studies. In 1885, Poincare introduced the notion of bifurcation, discussed the elements of the theory and described the phenomenon to an extremely detailed extent. The basic elements of the theory may be grouped into three areas: critical solutions, dynamic stability and structural stability. Our work concerns the area of structural stability, namely we use the topological degree theory methods to get local and global bifurcation results.

We report the results of a sensitive search for the minor isotopologues of water, H2-17O and H2-1... more We report the results of a sensitive search for the minor isotopologues of water, H2-17O and H2-18O, toward the carbon-rich AGB star IRC+10216 (a.k.a. CW Leonis) using the HIFI instrument on the Herschel Space Observatory. This search was motivated by the fact that any detection of isotopic enhancement in the H2-17O and H2-18O abundances would have strongly implicated CO photodissociation as the source of the atomic oxygen needed to produce water in a carbon-rich circumstellar envelope. Our observations place an upper limit of 1/470 on the H2-17O/H2-16O abundance ratio. Given the isotopic 17O/16O ratio of 1/840 inferred previously for the photosphere of IRC+10216, this result places an upper limit of a factor 1.8 on the extent of any isotope-selective enhancement of H2-17O in the circumstellar material, and provides an important constraint on any model that invokes CO photodissociation as the source of O for H2O production. In the context of the clumpy photodissociation model proposed previously for the origin of water in IRC+10216, our limit implies that 12C-16O (not 13C-16O or SiO) must be the dominant source of 16O for H2O production, and that the effects of self-shielding can only have reduced the 12C-16O photodissociation rate by at most a factor ~ 2.

The Astrophysical Journal Letters, Jan 3, 2011

We report the results of observations of ten rotational transitions of water vapor toward the car... more We report the results of observations of ten rotational transitions of water vapor toward the carbonrich AGB (asymptotic giant branch) star IRC+10216 (CW Leonis), carried out with Herschel's HIFI instrument. Each transition was securely detected by means of observations using the dual beam switch mode of HIFI. The measured line ratios imply that water vapor is present in the inner outflow at small distances (≤ few × 10 14 cm) from the star, confirming recent results reported by Decin et al. from observations with Herschel's PACS and SPIRE instruments. This finding definitively rules out the hypothesis that the observed water results from the vaporization of small icy objects in circular orbits. The origin of water within the dense C-rich envelope of IRC+10216 remains poorly understood. We derive upper limits on the H 17 2 O/H 16 2 O and H 18 2 O/H 16 2 O isotopic abundance ratios of ∼ 5 × 10 −3 (3 σ), providing additional constraints on models for the origin of the water vapor in IRC+10216.

We present optical and infrared spectroscopy of V1309 Sco, an object that erupted in 2008 in a st... more We present optical and infrared spectroscopy of V1309 Sco, an object that erupted in 2008 in a stellar-merger event. During the outburst, V1309 Sco displayed characteristics typical of red transients, a class of objects similar to V838 Mon. Our observations were obtained in 2009 and 2012, i.e. months and years after the eruption of V1309 Sco, and illustrate severe changes in the remnant, mainly in its circumstellar surroundings. In addition to atomic gas observed in earlier epochs, we identified molecular bands of TiO, VO, H 2 O, ScO, AlO, and CrO. The infrared bands of CrO we analyse are the first astronomical identification of the features. Over the whole period covered by our data, the remnant was associated with a cool ( 1000 K) outflow with a terminal velocity of about 200 km s −1 . Signatures of warmer atomic gas, likely to be still dissipating the energy of the 2008 outburst, dramatically decreased their brightness between 2009 and 2012. In addition, the source of optical continuum disappeared sometime before 2012, likely owing to the formation of new dust. The final stage of V1309 Sco's evolution captured by our spectra is an object remarkably similar to an older red transient, V4332 Sgr. In addition to providing a detailed view on the settling of the eruptive object, the observations presented here reinforce the conclusion that all the Galactic red transients are a manifestation of the same phenomenon, i.e. a stellar merger. The late spectra of V1309 Sco also suggest peculiarities in the chemical composition of the remnant, which still need to be explored.

Astronomy & Astrophysics, 2015

We present optical and infrared spectroscopy of V1309 Sco, an object which erupted in 2008 in a s... more We present optical and infrared spectroscopy of V1309 Sco, an object which erupted in 2008 in a stellar-merger event. During the outburst, V1309 Sco displayed characteristics typical for red transients, a class of objects similar to V838 Mon. Our observations were obtained in 2009 and 2012, i.e. months and years after the eruption of V1309 Sco, and illustrate severe changes in the remnant, mainly in its circumstellar surroundings. In addition to atomic gas observed in earlier epochs, we identified molecular bands of TiO, VO, H 2 O, ScO, AlO, and CrO. Infrared bands of CrO we analyze are first astronomical identification of those features. Over the whole period covered by our data, the remnant was associated with a cool ( 1000 K) outflow with a terminal velocity of about 200 km s −1 . Signatures of warmer atomic gas, likely to be still dissipating the energy of the 2008 outburst, dramatically decreased their brightness between 2009 and 2012. Also, sometime before 2012 the source of optical continuum disappeared, likely owing to formation of new dust. The final stage captured by our spectra show an object remarkably similar to an older red transient, V4332 Sgr. In addition to providing a detailed view on the settling of the eruptive object, the observations presented here reinforce the conclusion that all the Galactic red transients are a manifestation of the same phenomenon, i.e. a stellar merger. Also, the late spectra of V1309 Sco suggest pecularities in the chemical composition of the remnant, which yet need to be explored.

We report the results of observations of ten rotational transitions of water vapor toward the car... more We report the results of observations of ten rotational transitions of water vapor toward the carbon-rich AGB (asymptotic giant branch) star IRC+10216 (CW Leonis), carried out with Herschel's HIFI instrument. Each transition was securely detected by means of observations using the dual beam switch mode of HIFI. The measured line ratios imply that water vapor is present in the inner outflow at small distances (few x 1.E+14 cm) from the star, confirming recent results reported by Decin et al. from observations with Herschel's PACS and SPIRE instruments. This finding definitively rules out the hypothesis that the observed water results from the vaporization of small icy objects in circular orbits. The origin of water within the dense C-rich envelope of IRC+10216 remains poorly understood. We derive upper limits on the H2-17O/H2-16O and H2-18O/H2-16O isotopic abundance ratios of ~ 5.E-3 (3 sigma), providing additional constraints on models for the origin of the water vapor in IR...

ESO Astrophysics Symposia, 1998

ESO Astrophysics Symposia, 1998

ESO Astrophysics Symposia, 1998

Proceedings of the International Astronomical Union, 2008

We present high-resolution and high signal-to-noise spectroscopic observations of interstellar mo... more We present high-resolution and high signal-to-noise spectroscopic observations of interstellar molecular lines of C2 towards early-type stars. C2 is particularly interesting because it is the simplest multicarbon molecule and its abundances give information on the chemistry of interstellar clouds, especially on the pathway of formation of (hydro)carbon chains and PAHs which may be considered as possible carriers of diffuse interstellar bands (DIBs). Homonuclear diatomic molecules have negligible dipol moments and hence radiative cooling of excited rotational levels may go only trough the slow quadrupole transitions (van Dishoeck & Black 1982). In C2, pumped by galactic average interstellar field rotational levels are excited effectively much above the gas kinetic temperature and a rotational ladder of electronic transitions is usually observed from high rotational levels. Relations between abundances of the dicarbon and other simple interstellar molecules are considered as well.

The Astrophysical Journal, 2011

We report the results of observations of ten rotational transitions of water vapor toward the car... more We report the results of observations of ten rotational transitions of water vapor toward the carbonrich AGB (asymptotic giant branch) star IRC+10216 (CW Leonis), carried out with Herschel's HIFI instrument. Each transition was securely detected by means of observations using the dual beam switch mode of HIFI. The measured line ratios imply that water vapor is present in the inner outflow at small distances (≤ few × 10 14 cm) from the star, confirming recent results reported by Decin et al. from observations with Herschel's PACS and SPIRE instruments. This finding definitively rules out the hypothesis that the observed water results from the vaporization of small icy objects in circular orbits. The origin of water within the dense C-rich envelope of IRC+10216 remains poorly understood. We derive upper limits on the H 17 2 O/H 16 2 O and H 18 2 O/H 16 2 O isotopic abundance ratios of ∼ 5 × 10 −3 (3 σ), providing additional constraints on models for the origin of the water vapor in IRC+10216.

The Astrophysical Journal, 2013

We report the results of a sensitive search for the minor isotopologues of water, H 17 2 O and H ... more We report the results of a sensitive search for the minor isotopologues of water, H 17 2 O and H 18 2 O, toward the carbon-rich AGB star IRC+10216 (a.k.a. CW Leonis) using the HIFI instrument on the Herschel Space Observatory. This search was motivated by the fact that any detection of isotopic enhancement in the H 17 2 O and H 18 2 O abundances would have strongly implicated CO photodissociation as the source of the atomic oxygen needed to produce water in a carbon-rich circumstellar envelope. Our observations place an upper limit of 1/470 on the H 17 2 O/H 16 2 O abundance ratio. Given the isotopic 17 O/ 16 O ratio of 1/840 inferred previously for the photosphere of IRC+10216, this result places an upper limit * Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA