The supernova SN1986j resembles the prototypical Type V supernova SN1961v in the relatively slow ... more The supernova SN1986j resembles the prototypical Type V supernova SN1961v in the relatively slow ∼1000km/s expansion velocity, the slow light curve, and also in the Hα dominated spectrum. The optical spectrum is similar to the spectra of some novae, and some OB stars with massive winds, being characteristic of a nebular plasma at about 1010cm−3 and 104K. What makes SN1986j exceptional is its tremendous radio luminosity, the brightest radio supernova observed to date. The radio emission indicates the presence of a massive circumstellar wind, with which the SN ejecta are now colliding. Since the cooling time of the optically emitting gas is about an hour, a heat source is required to power the light curve. Shocks moving back into the ejecta offer a natural heat source, and account quantitatively for the observed luminosity and spectral character of SN1986j. The large Hα/Hβ ratio is attributed to trapping of Ly α, which pumps the n = 2 level of hydrogen, causing a finite optical depth ...
As part of an ongoing program to better understand the early stages of massive star cluster evolu... more As part of an ongoing program to better understand the early stages of massive star cluster evolution and the physical conditions required for their formation, we have obtained 10 μm (N-band) images with Gemini North of the nuclear region of the starburst galaxy He 2-10. Five massive star clusters still enshrouded in their natal cocoons with no optical counterparts were previously discovered by Kobulnicky & Johnson (1999) as optically thick thermal radio sources. Three of these five radio sources have strong 10 μm detections in only 10 minutes of integration time with Gemini. The blackbody temperatures of the dust cocoons are estimated to range from ∼ 40 — 150 K at their outer and inner edges, and the mass of these dust shells is ∼ 107 M⊙. The ages of the embedded stellar clusters must be < 106 years. The bolometric luminosities of the exciting clusters can be constrained to ∼ 108–9 L⊙, and the implied masses are > 106 M⊙. These three embedded clusters are responsible for at l...
The field-imaging far-infrared line spectrometer (FIFI-LS) is a science instrument for the Strato... more The field-imaging far-infrared line spectrometer (FIFI-LS) is a science instrument for the Stratospheric Observatory for Infrared Astronomy (SOFIA). FIFI-LS allows simultaneous observations in two spectral channels. The “blue” channel is sensitive from 51[Formula: see text][Formula: see text]m to 125[Formula: see text][Formula: see text]m and the “red” channel from 115[Formula: see text][Formula: see text]m to 203[Formula: see text][Formula: see text]m. The instantaneous spectral coverage is 1000–3000[Formula: see text]km/s in the blue and 800–2500[Formula: see text]km/s in the red channel with a spectral resolution between 150[Formula: see text]km/s and 600[Formula: see text]km/s. Each spectral channel observes a field of five by five spatial pixels on the sky. The pixel size in the blue channel is 6.14 by 6.25 square arc seconds and it is 12.2 by 12.5 square arc seconds in the red channel. FIFI-LS has been operating on SOFIA since 2014. It is available to the astronomical communit...
Symposium - International Astronomical Union, 1999
Using the latest stellar evolution models, theoretical stellar spectra, and a compilation of obse... more Using the latest stellar evolution models, theoretical stellar spectra, and a compilation of observed emission line strengths from Wolf-Rayet (WR) stars, we have constructed evolutionary synthesis models for young starbursts (Schaerer…
Based on new spectra spanning wavelengths from 0.8 to 2.4μm, we study the properties of bright ne... more Based on new spectra spanning wavelengths from 0.8 to 2.4μm, we study the properties of bright near-IR clusters in M82. We focus on age and extinction, which are critical parameters when one uses dynamical masses to constrain the stellar IMF. The modelling of red supergiant evolution by various authors leads to very significant differences in synthetic cluster spectra. Near-IR fluxes alone therefore do not rule out a normal IMF for cluster F, previously found to be deficient in low mass stars. Combined optical and near-IR studies are being undertaken.
Symposium - International Astronomical Union, 2003
We present the initial results of a medium resolution, 0.8 to 4.2 μm spectroscopic survey of M, L... more We present the initial results of a medium resolution, 0.8 to 4.2 μm spectroscopic survey of M, L, and T dwarfs. We have identified the most prominent molecular and atomic absorption features found in the spectra of these late-type dwarfs. We have also compared the spectra to a laboratory FeH emission spectrum and identified nearly 100 features common to the FeH spectrum and the dwarf spectra from 0.99 to 1.8 μm.
The nuclear starburst in M82 is host to over 20 infrared-bright, dense, young super star clusters... more The nuclear starburst in M82 is host to over 20 infrared-bright, dense, young super star clusters (SSCs). We use high-resolution near-infrared Keck/NIRSPEC echelle spectroscopy to measure the stellar velocity dispersions. The SSCs are resolved in Hubble Space Telescope images, from which we measure half-light radii and integrated luminosities. We calculate virial masses for the SSCs, and compare the observed light-to-mass
Symposium - International Astronomical Union, 2003
N-band (10.8 μm) imaging of the blue compact starburst galaxy He 2-10 reveals the presence of fou... more N-band (10.8 μm) imaging of the blue compact starburst galaxy He 2-10 reveals the presence of four emission regions, which have no optical or near-IR counterparts. These sources correspond to the ‘ultradense H ii’ regions recently identified in 2cm and 6cm radio maps of this galaxy. We have used the N-band data to place constraints on the properties of the stellar clusters, that are deeply embedded within these dust-emitting regions.
Bulletin of the American Astronomical Society, 1993
We present a study of the massive star content of 30 Dor using a population synthesis model in th... more We present a study of the massive star content of 30 Dor using a population synthesis model in the ultraviolet. The relatively small distance to the LMC allows one to spatially resolve the individual components in 30 Dor. This property offers an important test for theoretical models. UV spectra of the central region of 30 Dor have been collected with IUE by trailing the entrance aperture across the central 1' times 1' and 3' times 3' region. Using our model, we synthesize as a function of time the monochromatic luminosity from 912 to 10000 Angstroms, the number of ionizing photons emitted shortward of 912 Angstroms (NLy), the UV lines of SiIV, CIV and HeII, the spectral type following from the stellar parameters and the evolutionary status. We generated a series of starburst models for the two limiting cases of a continuous and an instantaneous burst. A Salpeter-type IMF with alpha = 2.35 is adopted and two metallicities, Z_sun and 0.25Z_sun, are considered. The modeling of the UV spectrum provides a stringent limit on the age and the IMF upper cut-off mass for the central regions of 30 Dor. The flux level depends on the age and the upper cut-off mass. Combining the results for the instantaneous and the continuous scenarios, we find that the age of the observed region is less than 5 Myr. The observations cannot be matched for an upper cut-off mass less then 50 M_sun. The conclusions reached from the synthesis of the UV lines are very consistent considering the fact that we are here limited by a spectral library at solar metallicity. The SiIV, CIV and HeII lines offer characteristics which are very sensitive to the massive star content. For example, evolved massive stars display a strong P Cygni profile of SiIV with a large velocity shift to the blue due to Doppler effect in their fast and dense stellar winds. Based on the synthesis of the lines alone (at Z_sun), an age of 3 Myr is found for the central regions of 30 Dor, again with an upper cut-off mass larger than 50 M_sun. The number of O and Wolf-Rayet stars observed and classified in the central region of 30 Dor are well reproduced.
The supernova SN1986j resembles the prototypical Type V supernova SN1961v in the relatively slow ... more The supernova SN1986j resembles the prototypical Type V supernova SN1961v in the relatively slow ∼1000km/s expansion velocity, the slow light curve, and also in the Hα dominated spectrum. The optical spectrum is similar to the spectra of some novae, and some OB stars with massive winds, being characteristic of a nebular plasma at about 1010cm−3 and 104K. What makes SN1986j exceptional is its tremendous radio luminosity, the brightest radio supernova observed to date. The radio emission indicates the presence of a massive circumstellar wind, with which the SN ejecta are now colliding. Since the cooling time of the optically emitting gas is about an hour, a heat source is required to power the light curve. Shocks moving back into the ejecta offer a natural heat source, and account quantitatively for the observed luminosity and spectral character of SN1986j. The large Hα/Hβ ratio is attributed to trapping of Ly α, which pumps the n = 2 level of hydrogen, causing a finite optical depth ...
As part of an ongoing program to better understand the early stages of massive star cluster evolu... more As part of an ongoing program to better understand the early stages of massive star cluster evolution and the physical conditions required for their formation, we have obtained 10 μm (N-band) images with Gemini North of the nuclear region of the starburst galaxy He 2-10. Five massive star clusters still enshrouded in their natal cocoons with no optical counterparts were previously discovered by Kobulnicky & Johnson (1999) as optically thick thermal radio sources. Three of these five radio sources have strong 10 μm detections in only 10 minutes of integration time with Gemini. The blackbody temperatures of the dust cocoons are estimated to range from ∼ 40 — 150 K at their outer and inner edges, and the mass of these dust shells is ∼ 107 M⊙. The ages of the embedded stellar clusters must be < 106 years. The bolometric luminosities of the exciting clusters can be constrained to ∼ 108–9 L⊙, and the implied masses are > 106 M⊙. These three embedded clusters are responsible for at l...
The field-imaging far-infrared line spectrometer (FIFI-LS) is a science instrument for the Strato... more The field-imaging far-infrared line spectrometer (FIFI-LS) is a science instrument for the Stratospheric Observatory for Infrared Astronomy (SOFIA). FIFI-LS allows simultaneous observations in two spectral channels. The “blue” channel is sensitive from 51[Formula: see text][Formula: see text]m to 125[Formula: see text][Formula: see text]m and the “red” channel from 115[Formula: see text][Formula: see text]m to 203[Formula: see text][Formula: see text]m. The instantaneous spectral coverage is 1000–3000[Formula: see text]km/s in the blue and 800–2500[Formula: see text]km/s in the red channel with a spectral resolution between 150[Formula: see text]km/s and 600[Formula: see text]km/s. Each spectral channel observes a field of five by five spatial pixels on the sky. The pixel size in the blue channel is 6.14 by 6.25 square arc seconds and it is 12.2 by 12.5 square arc seconds in the red channel. FIFI-LS has been operating on SOFIA since 2014. It is available to the astronomical communit...
Symposium - International Astronomical Union, 1999
Using the latest stellar evolution models, theoretical stellar spectra, and a compilation of obse... more Using the latest stellar evolution models, theoretical stellar spectra, and a compilation of observed emission line strengths from Wolf-Rayet (WR) stars, we have constructed evolutionary synthesis models for young starbursts (Schaerer…
Based on new spectra spanning wavelengths from 0.8 to 2.4μm, we study the properties of bright ne... more Based on new spectra spanning wavelengths from 0.8 to 2.4μm, we study the properties of bright near-IR clusters in M82. We focus on age and extinction, which are critical parameters when one uses dynamical masses to constrain the stellar IMF. The modelling of red supergiant evolution by various authors leads to very significant differences in synthetic cluster spectra. Near-IR fluxes alone therefore do not rule out a normal IMF for cluster F, previously found to be deficient in low mass stars. Combined optical and near-IR studies are being undertaken.
Symposium - International Astronomical Union, 2003
We present the initial results of a medium resolution, 0.8 to 4.2 μm spectroscopic survey of M, L... more We present the initial results of a medium resolution, 0.8 to 4.2 μm spectroscopic survey of M, L, and T dwarfs. We have identified the most prominent molecular and atomic absorption features found in the spectra of these late-type dwarfs. We have also compared the spectra to a laboratory FeH emission spectrum and identified nearly 100 features common to the FeH spectrum and the dwarf spectra from 0.99 to 1.8 μm.
The nuclear starburst in M82 is host to over 20 infrared-bright, dense, young super star clusters... more The nuclear starburst in M82 is host to over 20 infrared-bright, dense, young super star clusters (SSCs). We use high-resolution near-infrared Keck/NIRSPEC echelle spectroscopy to measure the stellar velocity dispersions. The SSCs are resolved in Hubble Space Telescope images, from which we measure half-light radii and integrated luminosities. We calculate virial masses for the SSCs, and compare the observed light-to-mass
Symposium - International Astronomical Union, 2003
N-band (10.8 μm) imaging of the blue compact starburst galaxy He 2-10 reveals the presence of fou... more N-band (10.8 μm) imaging of the blue compact starburst galaxy He 2-10 reveals the presence of four emission regions, which have no optical or near-IR counterparts. These sources correspond to the ‘ultradense H ii’ regions recently identified in 2cm and 6cm radio maps of this galaxy. We have used the N-band data to place constraints on the properties of the stellar clusters, that are deeply embedded within these dust-emitting regions.
Bulletin of the American Astronomical Society, 1993
We present a study of the massive star content of 30 Dor using a population synthesis model in th... more We present a study of the massive star content of 30 Dor using a population synthesis model in the ultraviolet. The relatively small distance to the LMC allows one to spatially resolve the individual components in 30 Dor. This property offers an important test for theoretical models. UV spectra of the central region of 30 Dor have been collected with IUE by trailing the entrance aperture across the central 1' times 1' and 3' times 3' region. Using our model, we synthesize as a function of time the monochromatic luminosity from 912 to 10000 Angstroms, the number of ionizing photons emitted shortward of 912 Angstroms (NLy), the UV lines of SiIV, CIV and HeII, the spectral type following from the stellar parameters and the evolutionary status. We generated a series of starburst models for the two limiting cases of a continuous and an instantaneous burst. A Salpeter-type IMF with alpha = 2.35 is adopted and two metallicities, Z_sun and 0.25Z_sun, are considered. The modeling of the UV spectrum provides a stringent limit on the age and the IMF upper cut-off mass for the central regions of 30 Dor. The flux level depends on the age and the upper cut-off mass. Combining the results for the instantaneous and the continuous scenarios, we find that the age of the observed region is less than 5 Myr. The observations cannot be matched for an upper cut-off mass less then 50 M_sun. The conclusions reached from the synthesis of the UV lines are very consistent considering the fact that we are here limited by a spectral library at solar metallicity. The SiIV, CIV and HeII lines offer characteristics which are very sensitive to the massive star content. For example, evolved massive stars display a strong P Cygni profile of SiIV with a large velocity shift to the blue due to Doppler effect in their fast and dense stellar winds. Based on the synthesis of the lines alone (at Z_sun), an age of 3 Myr is found for the central regions of 30 Dor, again with an upper cut-off mass larger than 50 M_sun. The number of O and Wolf-Rayet stars observed and classified in the central region of 30 Dor are well reproduced.
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