Proceedings of the International Astronomical Union, 2006
We report on new results of our multiplicity study and present our follow-up observations of the ... more We report on new results of our multiplicity study and present our follow-up observations of the recently detected faint companion HD 3651 B, the first directly imaged T dwarf companion of an exoplanet host star.
Ground-based and Airborne Instrumentation for Astronomy III, 2010
METIS is a mid-infrared instrument proposed for the European Extremely Large Telescope (E-ELT). I... more METIS is a mid-infrared instrument proposed for the European Extremely Large Telescope (E-ELT). It is designed to provide imaging and spectroscopic capabilities in the 3 -14 μm region up to a spectral resolution of 10 5 . One of the novel concepts of METIS is that of a high-resolution integral field spectrograph (IFS) for a diffraction-limited mid-IR instrument. While this concept has many scientific and operational advantages over a long-slit spectrograph, one drawback is that the spectral resolution changes over the field of view. This has an impact on the procedures to correct for telluric absorption lines imprinted on the science spectra. They are a major obstacle in the quest to maximize spectral fidelity, the ability to distinguish a weak spectral feature from the continuum. The classical technique of division by a standard star spectrum, observed in a single IFS spaxel, cannot simply be applied to all spaxels, because the spectral resolution changes from spaxel to spaxel. Here we present and discuss possible techniques of telluric line correction of METIS IFS spectra, including the application of synthetic model spectra of telluric transmission, to maximize spectral fidelity.
We present high-precision relative radial velocities of the very low-mass star VB 10 that were ob... more We present high-precision relative radial velocities of the very low-mass star VB 10 that were obtained over a time span of 0.61 yr as part of an ongoing search for planets around stars at the end of the main sequence. The radial velocities were measured from high-resolution near-infrared spectra obtained using the CRIRES instrument on the VLT with an ammonia gas cell. The typical internal precision of the measurements is 10 m s −1 . These data do not exhibit significant variability and are essentially constant at a level consistent with the measurement uncertainties. Therefore, we do not detect the radial velocity variations of VB 10 expected due to the presence of an orbiting giant planet similar to that recently proposed by Pravdo and Shaklan based on apparent astrometric perturbations. In addition, we do not confirm the ∼ 1 km s −1 radial velocity variability of the star tentatively detected by Zapatero Osorio and colleagues with lower precision measurements. Our measurements rule out planets with M p > 3 M Jup and the orbital period and inclination suggested by Pravdo and Shaklan at better than 5 σ confidence. We conclude that the planet detection claimed by Pravdo and Shaklan is spurious on the basis of this result. Although the outcome of this work is a non-detection, it illustrates the potential of using ammonia cell radial velocities to detect planets around very low-mass stars.
We present high-precision relative radial velocities of the very low mass star VB 10 that were ob... more We present high-precision relative radial velocities of the very low mass star VB 10 that were obtained over a time span of 0.61 years as part of an ongoing search for planets around stars at the end of the main sequence. The radial velocities were measured from high-resolution near-infrared spectra obtained using the CRIRES instrument on the Very Large Telescope with an ammonia gas cell. The typical internal precision of the measurements is 10 m s −1 . These data do not exhibit significant variability and are essentially constant at a level consistent with the measurement uncertainties. Therefore, we do not detect the radial velocity variations of VB 10 expected due to the presence of an orbiting giant planet similar to that recently proposed by Pravdo & Shaklan based on apparent astrometric perturbations. In addition, we do not confirm the ∼1 km s −1 radial velocity variability of the star tentatively detected by Zapatero Osorio and colleagues with lower precision measurements. Our measurements rule out planets with M p > 3 M Jup and the orbital period and inclination suggested by Pravdo & Shaklan at better than 5σ confidence. We conclude that the planet detection claimed by Pravdo & Shaklan is spurious on the basis of this result. Although the outcome of this work is a non-detection, it illustrates the potential of using ammonia cell radial velocities to detect planets around very low mass stars.
Aims. We present first quantitative results of the surface magnetic field measurements in selecte... more Aims. We present first quantitative results of the surface magnetic field measurements in selected M-dwarfs based on detailed spectra synthesis conducted simultaneously in atomic and molecular lines of the FeH Wing-Ford F 4 ∆ − X 4 ∆ transitions. Methods. A modified version of the Molecular Zeeman Library (MZL) was used to compute Landé g-factors for FeH lines in different Hund's cases. Magnetic spectra synthesis was performed with the Synmast code. Results. We show that the implementation of different Hund's case for FeH states depending on their quantum numbers allows us to achieve a good fit to the majority of lines in a sunspot spectrum in an automatic regime. Strong magnetic fields are confirmed via the modelling of atomic and FeH lines for three M-dwarfs YZ CMi, EV Lac, and AD Leo, but their mean intensities are found to be systematically lower than previously reported. A much weaker field (1.7 − 2 kG against 2.7 kG) is required to fit FeH lines in the spectra of GJ 1224. Conclusions. Our method allows us to measure average magnetic fields in very low-mass stars from polarized radiative transfer. The obtained results indicate that the fields reported in earlier works were probably overestimated by about 15 − 30%. Higher quality observations are needed for more definite results.
In our ongoing survey for wide (sub)stellar companions of exoplanet host stars we have found 4 ne... more In our ongoing survey for wide (sub)stellar companions of exoplanet host stars we have found 4 new co-moving stellar companions of the stars HD 114729, HD 16141, HD 196050 and HD 213240 with projected separations from 223 up to 3898 AU. The companionship of HD 114729 B, HD 196050 B and HD 213240 C is confirmed by photometry and spectroscopy, all being early M dwarfs. The masses of the detected companions are derived from their infrared JHK magnitudes and range between 0.146 and 0.363 M ⊙ . Our first and second epoch observations can rule out additional stellar companions around the primaries from ∼ 200 up to ∼ 2400 AU (S/N=10).
We search for stellar and substellar companions of young nearby stars to investigate stellar mult... more We search for stellar and substellar companions of young nearby stars to investigate stellar multiplicity and formation of stellar and substellar companions. We detect common proper-motion companions of stars via multi-epoch imaging. Their companionship is finally confirmed with photometry and spectroscopy. Here we report the discovery of a new co-moving (13 σ) stellar companion ∼ 17.8 arcsec (350 AU in projected separation) north of the nearby star HD 141272 (21 pc). With EMMI/NTT optical spectroscopy we determined the spectral type of the companion to be M3±0.5V. The derived spectral type as well as the near infrared photometry of the companion are both fully consistent with a 0.26 +0.07 −0.06 M⊙ dwarf located at the distance of HD 141272 (21 pc). Furthermore the photometry data rules out the pre-main sequence status, since the system is consistent with the ZAMS of the Pleiades.
Strong surface magnetic fields are ubiquitously found in M-dwarfs with mean intensities on the or... more Strong surface magnetic fields are ubiquitously found in M-dwarfs with mean intensities on the order of few thousand Gauss -three orders of magnitude higher than the mean surface magnetic field of the Sun. These fields and their interaction with photospheric convection are the main source of stellar activity, which is of big interest to study links between parent stars and their planets. Moreover, the understanding of stellar magnetism, as well as the role of different dynamo-actions in particular, is impossible without explaining magnetic fields in M-dwarfs. Measuring magnetic field intensities and geometries in such cool objects, however, is strongly limited to our ability to simulate the Zeeman effect in molecular lines. In this work, we present quantitative results of modelling and analysis of the magnetic fields in selected M-dwarfs in FeH Wing-Ford lines and strong atomic lines. Some particular FeH lines are found to be the excellent probes of the magnetic field.
Proceedings of the International Astronomical Union, 2006
We report on new results of our multiplicity study and present our follow-up observations of the ... more We report on new results of our multiplicity study and present our follow-up observations of the recently detected faint companion HD 3651 B, the first directly imaged T dwarf companion of an exoplanet host star.
Ground-based and Airborne Instrumentation for Astronomy III, 2010
METIS is a mid-infrared instrument proposed for the European Extremely Large Telescope (E-ELT). I... more METIS is a mid-infrared instrument proposed for the European Extremely Large Telescope (E-ELT). It is designed to provide imaging and spectroscopic capabilities in the 3 -14 μm region up to a spectral resolution of 10 5 . One of the novel concepts of METIS is that of a high-resolution integral field spectrograph (IFS) for a diffraction-limited mid-IR instrument. While this concept has many scientific and operational advantages over a long-slit spectrograph, one drawback is that the spectral resolution changes over the field of view. This has an impact on the procedures to correct for telluric absorption lines imprinted on the science spectra. They are a major obstacle in the quest to maximize spectral fidelity, the ability to distinguish a weak spectral feature from the continuum. The classical technique of division by a standard star spectrum, observed in a single IFS spaxel, cannot simply be applied to all spaxels, because the spectral resolution changes from spaxel to spaxel. Here we present and discuss possible techniques of telluric line correction of METIS IFS spectra, including the application of synthetic model spectra of telluric transmission, to maximize spectral fidelity.
We present high-precision relative radial velocities of the very low-mass star VB 10 that were ob... more We present high-precision relative radial velocities of the very low-mass star VB 10 that were obtained over a time span of 0.61 yr as part of an ongoing search for planets around stars at the end of the main sequence. The radial velocities were measured from high-resolution near-infrared spectra obtained using the CRIRES instrument on the VLT with an ammonia gas cell. The typical internal precision of the measurements is 10 m s −1 . These data do not exhibit significant variability and are essentially constant at a level consistent with the measurement uncertainties. Therefore, we do not detect the radial velocity variations of VB 10 expected due to the presence of an orbiting giant planet similar to that recently proposed by Pravdo and Shaklan based on apparent astrometric perturbations. In addition, we do not confirm the ∼ 1 km s −1 radial velocity variability of the star tentatively detected by Zapatero Osorio and colleagues with lower precision measurements. Our measurements rule out planets with M p > 3 M Jup and the orbital period and inclination suggested by Pravdo and Shaklan at better than 5 σ confidence. We conclude that the planet detection claimed by Pravdo and Shaklan is spurious on the basis of this result. Although the outcome of this work is a non-detection, it illustrates the potential of using ammonia cell radial velocities to detect planets around very low-mass stars.
We present high-precision relative radial velocities of the very low mass star VB 10 that were ob... more We present high-precision relative radial velocities of the very low mass star VB 10 that were obtained over a time span of 0.61 years as part of an ongoing search for planets around stars at the end of the main sequence. The radial velocities were measured from high-resolution near-infrared spectra obtained using the CRIRES instrument on the Very Large Telescope with an ammonia gas cell. The typical internal precision of the measurements is 10 m s −1 . These data do not exhibit significant variability and are essentially constant at a level consistent with the measurement uncertainties. Therefore, we do not detect the radial velocity variations of VB 10 expected due to the presence of an orbiting giant planet similar to that recently proposed by Pravdo & Shaklan based on apparent astrometric perturbations. In addition, we do not confirm the ∼1 km s −1 radial velocity variability of the star tentatively detected by Zapatero Osorio and colleagues with lower precision measurements. Our measurements rule out planets with M p > 3 M Jup and the orbital period and inclination suggested by Pravdo & Shaklan at better than 5σ confidence. We conclude that the planet detection claimed by Pravdo & Shaklan is spurious on the basis of this result. Although the outcome of this work is a non-detection, it illustrates the potential of using ammonia cell radial velocities to detect planets around very low mass stars.
Aims. We present first quantitative results of the surface magnetic field measurements in selecte... more Aims. We present first quantitative results of the surface magnetic field measurements in selected M-dwarfs based on detailed spectra synthesis conducted simultaneously in atomic and molecular lines of the FeH Wing-Ford F 4 ∆ − X 4 ∆ transitions. Methods. A modified version of the Molecular Zeeman Library (MZL) was used to compute Landé g-factors for FeH lines in different Hund's cases. Magnetic spectra synthesis was performed with the Synmast code. Results. We show that the implementation of different Hund's case for FeH states depending on their quantum numbers allows us to achieve a good fit to the majority of lines in a sunspot spectrum in an automatic regime. Strong magnetic fields are confirmed via the modelling of atomic and FeH lines for three M-dwarfs YZ CMi, EV Lac, and AD Leo, but their mean intensities are found to be systematically lower than previously reported. A much weaker field (1.7 − 2 kG against 2.7 kG) is required to fit FeH lines in the spectra of GJ 1224. Conclusions. Our method allows us to measure average magnetic fields in very low-mass stars from polarized radiative transfer. The obtained results indicate that the fields reported in earlier works were probably overestimated by about 15 − 30%. Higher quality observations are needed for more definite results.
In our ongoing survey for wide (sub)stellar companions of exoplanet host stars we have found 4 ne... more In our ongoing survey for wide (sub)stellar companions of exoplanet host stars we have found 4 new co-moving stellar companions of the stars HD 114729, HD 16141, HD 196050 and HD 213240 with projected separations from 223 up to 3898 AU. The companionship of HD 114729 B, HD 196050 B and HD 213240 C is confirmed by photometry and spectroscopy, all being early M dwarfs. The masses of the detected companions are derived from their infrared JHK magnitudes and range between 0.146 and 0.363 M ⊙ . Our first and second epoch observations can rule out additional stellar companions around the primaries from ∼ 200 up to ∼ 2400 AU (S/N=10).
We search for stellar and substellar companions of young nearby stars to investigate stellar mult... more We search for stellar and substellar companions of young nearby stars to investigate stellar multiplicity and formation of stellar and substellar companions. We detect common proper-motion companions of stars via multi-epoch imaging. Their companionship is finally confirmed with photometry and spectroscopy. Here we report the discovery of a new co-moving (13 σ) stellar companion ∼ 17.8 arcsec (350 AU in projected separation) north of the nearby star HD 141272 (21 pc). With EMMI/NTT optical spectroscopy we determined the spectral type of the companion to be M3±0.5V. The derived spectral type as well as the near infrared photometry of the companion are both fully consistent with a 0.26 +0.07 −0.06 M⊙ dwarf located at the distance of HD 141272 (21 pc). Furthermore the photometry data rules out the pre-main sequence status, since the system is consistent with the ZAMS of the Pleiades.
Strong surface magnetic fields are ubiquitously found in M-dwarfs with mean intensities on the or... more Strong surface magnetic fields are ubiquitously found in M-dwarfs with mean intensities on the order of few thousand Gauss -three orders of magnitude higher than the mean surface magnetic field of the Sun. These fields and their interaction with photospheric convection are the main source of stellar activity, which is of big interest to study links between parent stars and their planets. Moreover, the understanding of stellar magnetism, as well as the role of different dynamo-actions in particular, is impossible without explaining magnetic fields in M-dwarfs. Measuring magnetic field intensities and geometries in such cool objects, however, is strongly limited to our ability to simulate the Zeeman effect in molecular lines. In this work, we present quantitative results of modelling and analysis of the magnetic fields in selected M-dwarfs in FeH Wing-Ford lines and strong atomic lines. Some particular FeH lines are found to be the excellent probes of the magnetic field.
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