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Papers by Gianluca Li Causi

The Astrophysical Journal, 2015

V1118 Ori is an eruptive variable belonging to the EXor class of Pre-Main Sequence stars whose ep... more V1118 Ori is an eruptive variable belonging to the EXor class of Pre-Main Sequence stars whose episodic outbursts are attributed to disk accretion events. Since 2006, V1118 Ori is in the longest quiescence stage ever observed between two subsequent outbursts of its recent history. We present near-infrared photometry of V1118 Ori carried out during the last eight years, along with a complete spectroscopic coverage from 0.35 to 2.5 µm. A longterm sampling of V1118 Ori in quiescence has never been done, hence we can benefit from the current circumstance to determine the lowest values (i.e. the zeroes) of the parameters to be used as a reference for evaluating the physical changes typical of more active phases. A quiescence mass accretion rate between 1-3 × 10 −9 M yr −1 can be derived and the difference with previous determinations is discussed. From line emission and IR colors analysis a visual extinction of 1-2 mag is consistently derived, confirming that V1118 Ori (at least in quiescence) is a low-extinction T Tauri star with a bolometric luminosity of about 2.1 L . An anti-correlation -2exists between the equivalent width of the emission lines and the underlying continuum. We searched the literature for evaluating whether or not such a behaviour is a common feature of the whole class. The anti-correlation is clearly recognizable for all the available EXors in the optical range (Hβ and Hα lines), while it is not as much evident in the infrared (Paβ and Brγ lines). The observed anti-correlation supports the accretion-driven mechanism as the most likely to account for continuum variations.

Astrophysics and Space Science, 2014

We present the collection of all the mid-and far-IR observations (λ=3-170µm) of the young eruptiv... more We present the collection of all the mid-and far-IR observations (λ=3-170µm) of the young eruptive variable PV Cep available so far in the literature. These data allow us to confirm that flux variability is a prominent feature at mid-IR wavelength (λ=3-25µm). Color-magnitude plots clearly indicate that the observed variability is not extinction-driven, but mainly influenced by fluctuations of the mass accretion rate. We interpret such variability as due to a hot spot created onto the stellar surface by the column of accreting matter, which heats the inner parts of the disk and determines the observed increase of the near-mid-IR luminosity. A quantitative characterization is given for both the spot itself and the additional thermal component created by it. are consistent with the presence of a temperature stratification in a massive and quite un-evolved circumstellar disk.

Proceedings of SPIE - The International Society for Optical Engineering, 2008

The VLTI Spectro Imager project aims to perform imaging with a temporal resolution of 1 night and... more The VLTI Spectro Imager project aims to perform imaging with a temporal resolution of 1 night and with a maximum angular resolution of 1 milliarcsecond, making best use of the Very Large Telescope Interferometer capabilities. To fulfill the scientific goals (see Garcia et. al.), the system requirements are: a) combining 4 to 6 beams; b) working in spectral bands J, H and K; c) spectral resolution from R= 100 to 12000; and d) internal fringe tracking on-axis, or offaxis when associated to the PRIMA dual-beam facility.

Science With the Vlt in the Elt Era, 2009

Nowadays, compact sources like surfaces of nearby stars, circumstellar environments of stars from... more Nowadays, compact sources like surfaces of nearby stars, circumstellar environments of stars from early stages to the most evolved ones and surroundings of active galactic nuclei can be investigated at milli-arcsecond scales only with the VLT in its interferometric mode. We propose a spectro-imager, named VSI (VLTI

... The correlation in Figure II, together with the consideration that an increased PAH luminosit... more ... The correlation in Figure II, together with the consideration that an increased PAH luminosity is related to an increased VSG -1 0 Log[ (AFA)I,/(AFA)Q} STRUCTURES AROUND HAEBE STARS 191 j 0 FIGURE II H~ luminosity vs. ...

During the preliminary phases of our project we have decided to systematically observe the type I... more During the preliminary phases of our project we have decided to systematically observe the type IIn supernova SN1999el discovered in the spiral galaxy NGC 6951 by Cao et al. (IAUC 7288, 1999). This supernova has been chosen because well sampled near-IR light curves of a type IIn are not available in literature so far. During this follow-up we have discovered, in the same galaxy, a type Ia new supernova, named SN2000E (Valentini el al. 2000, IAUC 7351). We present here the preliminary near-IR/optical light curves of both supernovae.

Astronomy & Astrophysics, 2013

Context. Optical-infrared interferometry can provide direct geometrical measurements of the radii... more Context. Optical-infrared interferometry can provide direct geometrical measurements of the radii of Cepheids and/or reveal unknown binary companions of these stars. Such information is of great importance for a proper calibration of Period-Luminosity relations and for determining binary fraction among Cepheids. Aims. We observed the Cepheid X Sgr with VLTI/AMBER in order to confirm or disprove the presence of the hypothesized binary companion and to directly measure the mean stellar radius, possibly detecting its variation along the pulsation cycle. Methods. From AMBER observations in MR mode we performed a binary model fitting on the closure phase and a limb-darkened model fitting on the visibility. Results. Our analysis indicates the presence of a point-like companion at a separation of 10.7 mas and 5.6 mag K fainter than the primary, whose flux and position are sharply constrained by the data. The radius pulsation is not detected, whereas the average limb-darkened diameter results to be 1.48±0.08 mas, corresponding to 53±3 R ⊙ . at a distance of 333.3 pc.

Proceedings of SPIE - The International Society for Optical Engineering, 2012

MOONS is a new conceptual design for a Multi-Object Optical and Near-infrared Spectrograph for th... more MOONS is a new conceptual design for a Multi-Object Optical and Near-infrared Spectrograph for the Very Large Telescope (VLT), selected by ESO for a Phase A study. The baseline design consists of ~1000 fibers deployable over a field of view of ~500 square arcmin, the largest patrol field offered by the Nasmyth focus at the VLT. The total wavelength coverage is 0.8µm-1.8µm and two resolution modes: medium resolution and high resolution. In the medium resolution mode (R~4,000-6,000) the entire wavelength range 0.8µm-1.8µm is observed simultaneously, while the high resolution mode covers simultaneously three selected spectral regions: one around the CaII triplet (at R~8,000) to measure radial velocities, and two regions at R~20,000 one in the J-band and one in the H-band, for detailed measurements of chemical abundances. The grasp of the 8.2m Very Large Telescope (VLT) combined with the large multiplex and wavelength coverage of MOONS -extending into the near-IR -will provide the observational power necessary to study galaxy formation and evolution over the entire history of the Universe, from our Milky Way, through the redshift desert and up to the epoch of re-ionization at z>8-9. At the same time, the high spectral resolution mode will allow astronomers to study chemical abundances of stars in our Galaxy, in particular in the highly obscured regions of the Bulge, and provide the necessary follow-up of the Gaia mission. Such characteristics and versatility make MOONS the long-awaited workhorse near-IR MOS for the VLT, which will perfectly complement optical spectroscopy performed by FLAMES and VIMOS.

The Astrophysical Journal, 2015

V1118 Ori is an eruptive variable belonging to the EXor class of Pre-Main Sequence stars whose ep... more V1118 Ori is an eruptive variable belonging to the EXor class of Pre-Main Sequence stars whose episodic outbursts are attributed to disk accretion events. Since 2006, V1118 Ori is in the longest quiescence stage ever observed between two subsequent outbursts of its recent history. We present near-infrared photometry of V1118 Ori carried out during the last eight years, along with a complete spectroscopic coverage from 0.35 to 2.5 µm. A longterm sampling of V1118 Ori in quiescence has never been done, hence we can benefit from the current circumstance to determine the lowest values (i.e. the zeroes) of the parameters to be used as a reference for evaluating the physical changes typical of more active phases. A quiescence mass accretion rate between 1-3 × 10 −9 M yr −1 can be derived and the difference with previous determinations is discussed. From line emission and IR colors analysis a visual extinction of 1-2 mag is consistently derived, confirming that V1118 Ori (at least in quiescence) is a low-extinction T Tauri star with a bolometric luminosity of about 2.1 L . An anti-correlation -2exists between the equivalent width of the emission lines and the underlying continuum. We searched the literature for evaluating whether or not such a behaviour is a common feature of the whole class. The anti-correlation is clearly recognizable for all the available EXors in the optical range (Hβ and Hα lines), while it is not as much evident in the infrared (Paβ and Brγ lines). The observed anti-correlation supports the accretion-driven mechanism as the most likely to account for continuum variations.

Astrophysics and Space Science, 2014

We present the collection of all the mid-and far-IR observations (λ=3-170µm) of the young eruptiv... more We present the collection of all the mid-and far-IR observations (λ=3-170µm) of the young eruptive variable PV Cep available so far in the literature. These data allow us to confirm that flux variability is a prominent feature at mid-IR wavelength (λ=3-25µm). Color-magnitude plots clearly indicate that the observed variability is not extinction-driven, but mainly influenced by fluctuations of the mass accretion rate. We interpret such variability as due to a hot spot created onto the stellar surface by the column of accreting matter, which heats the inner parts of the disk and determines the observed increase of the near-mid-IR luminosity. A quantitative characterization is given for both the spot itself and the additional thermal component created by it. are consistent with the presence of a temperature stratification in a massive and quite un-evolved circumstellar disk.

Proceedings of SPIE - The International Society for Optical Engineering, 2008

The VLTI Spectro Imager project aims to perform imaging with a temporal resolution of 1 night and... more The VLTI Spectro Imager project aims to perform imaging with a temporal resolution of 1 night and with a maximum angular resolution of 1 milliarcsecond, making best use of the Very Large Telescope Interferometer capabilities. To fulfill the scientific goals (see Garcia et. al.), the system requirements are: a) combining 4 to 6 beams; b) working in spectral bands J, H and K; c) spectral resolution from R= 100 to 12000; and d) internal fringe tracking on-axis, or offaxis when associated to the PRIMA dual-beam facility.

Science With the Vlt in the Elt Era, 2009

Nowadays, compact sources like surfaces of nearby stars, circumstellar environments of stars from... more Nowadays, compact sources like surfaces of nearby stars, circumstellar environments of stars from early stages to the most evolved ones and surroundings of active galactic nuclei can be investigated at milli-arcsecond scales only with the VLT in its interferometric mode. We propose a spectro-imager, named VSI (VLTI

... The correlation in Figure II, together with the consideration that an increased PAH luminosit... more ... The correlation in Figure II, together with the consideration that an increased PAH luminosity is related to an increased VSG -1 0 Log[ (AFA)I,/(AFA)Q} STRUCTURES AROUND HAEBE STARS 191 j 0 FIGURE II H~ luminosity vs. ...

During the preliminary phases of our project we have decided to systematically observe the type I... more During the preliminary phases of our project we have decided to systematically observe the type IIn supernova SN1999el discovered in the spiral galaxy NGC 6951 by Cao et al. (IAUC 7288, 1999). This supernova has been chosen because well sampled near-IR light curves of a type IIn are not available in literature so far. During this follow-up we have discovered, in the same galaxy, a type Ia new supernova, named SN2000E (Valentini el al. 2000, IAUC 7351). We present here the preliminary near-IR/optical light curves of both supernovae.

Astronomy & Astrophysics, 2013

Context. Optical-infrared interferometry can provide direct geometrical measurements of the radii... more Context. Optical-infrared interferometry can provide direct geometrical measurements of the radii of Cepheids and/or reveal unknown binary companions of these stars. Such information is of great importance for a proper calibration of Period-Luminosity relations and for determining binary fraction among Cepheids. Aims. We observed the Cepheid X Sgr with VLTI/AMBER in order to confirm or disprove the presence of the hypothesized binary companion and to directly measure the mean stellar radius, possibly detecting its variation along the pulsation cycle. Methods. From AMBER observations in MR mode we performed a binary model fitting on the closure phase and a limb-darkened model fitting on the visibility. Results. Our analysis indicates the presence of a point-like companion at a separation of 10.7 mas and 5.6 mag K fainter than the primary, whose flux and position are sharply constrained by the data. The radius pulsation is not detected, whereas the average limb-darkened diameter results to be 1.48±0.08 mas, corresponding to 53±3 R ⊙ . at a distance of 333.3 pc.

Proceedings of SPIE - The International Society for Optical Engineering, 2012

MOONS is a new conceptual design for a Multi-Object Optical and Near-infrared Spectrograph for th... more MOONS is a new conceptual design for a Multi-Object Optical and Near-infrared Spectrograph for the Very Large Telescope (VLT), selected by ESO for a Phase A study. The baseline design consists of ~1000 fibers deployable over a field of view of ~500 square arcmin, the largest patrol field offered by the Nasmyth focus at the VLT. The total wavelength coverage is 0.8µm-1.8µm and two resolution modes: medium resolution and high resolution. In the medium resolution mode (R~4,000-6,000) the entire wavelength range 0.8µm-1.8µm is observed simultaneously, while the high resolution mode covers simultaneously three selected spectral regions: one around the CaII triplet (at R~8,000) to measure radial velocities, and two regions at R~20,000 one in the J-band and one in the H-band, for detailed measurements of chemical abundances. The grasp of the 8.2m Very Large Telescope (VLT) combined with the large multiplex and wavelength coverage of MOONS -extending into the near-IR -will provide the observational power necessary to study galaxy formation and evolution over the entire history of the Universe, from our Milky Way, through the redshift desert and up to the epoch of re-ionization at z>8-9. At the same time, the high spectral resolution mode will allow astronomers to study chemical abundances of stars in our Galaxy, in particular in the highly obscured regions of the Bulge, and provide the necessary follow-up of the Gaia mission. Such characteristics and versatility make MOONS the long-awaited workhorse near-IR MOS for the VLT, which will perfectly complement optical spectroscopy performed by FLAMES and VIMOS.