Boncho Bonev | The Catholic University of America (original) (raw)

Papers by Boncho Bonev

The Planetary Science Journal, 2021

A major upgrade to the NIRSPEC instrument at the Keck II telescope was successfully completed in ... more A major upgrade to the NIRSPEC instrument at the Keck II telescope was successfully completed in time for near-infrared spectroscopic observations of comet 46P/Wirtanen during its exceptionally close flyby of Earth in 2018 December. These studies determined the abundances of several volatiles, including C2H2, C2H6, CH3OH, NH3, HCN, H2CO, and H2O. Long-slit spatial distributions of gas rotational temperature and column density are diagnostic for the presence of icy grains in the coma and understanding if different volatiles are associated with common or distinct outgassing sources. These spatial distributions suggest that C2H2, C2H6, and HCN have a common outgassing source, whereas H2O and CH3OH have additional, more extended sources. The synergy of these findings with observations by space missions (Rosetta and EPOXI) motivates continuing studies to address whether or not C2H6, C2H2, and HCN have a common source of release (plausibly associated with CO2) in a larger sample of comets...

The Astronomical Journal, 2020

The Astronomical Journal, 2019

The Astronomical Journal, 2017

The Astrophysical Journal, 2014

The Astrophysical Journal, 2005

The Astrophysical Journal, 2004

The Astrophysical Journal, 2008

The Astrophysical Journal, 2006

The Astrophysical Journal, 2007

The Astrophysical Journal, 2012

The Astrophysical Journal, 2008

The Astrophysical Journal, 2007

The Astrophysical Journal, 2006

The Astrophysical Journal, 2007

We present spatially resolved measurements of the rotational temperature and ortho-para ratio for... more We present spatially resolved measurements of the rotational temperature and ortho-para ratio for H 2 O in the inner coma of the Oort Cloud comet C/2004 Q2 (Machholz). Our results are based on direct simultaneous detections of ortho-H 2 O and para-H 2 O via "hot-band" fluorescence near 2.9 mm. We find a well-defined decline in rotational temperature with increasing nucleocentric distance (up to ∼1000 km). The ortho-para ratio remains constant (within stochastic uncertainty) with increasing nucleocentric distance and is close to the statistical equilibrium value of 3.0 ( [0.17], including, respectively, stochastic [systematic] uncertainty), resulting 2.86 ‫ע‬ 0.06 in spin temperature K. We compare the present results with those reported for other comets and discuss T ≥ 34 spin the difficulties in interpreting spin temperatures deduced from measured ortho-para ratios. Improved understanding of the special conditions that enable nuclear spin conversion would test the extent to which derived spin temperatures reflect the formative history or the processing record of cometary ices.

The Astrophysical Journal, 2013

The Astronomical Journal, 2013

We acquired near-infrared spectra of the Oort cloud comet C/2012 F6 (Lemmon) at three different h... more We acquired near-infrared spectra of the Oort cloud comet C/2012 F6 (Lemmon) at three different heliocentric distances (R h ) during the comet's 2013 perihelion passage, providing a comprehensive measure of the outgassing behavior of parent volatiles and cosmogonic indicators. Our observations were performed pre-perihelion at R h = 1.2 AU with CRIRES (on 2013 February 2 and 4), and post-perihelion at R h = 0.75 AU with CSHELL (on March 31 and April 1) and R h = 1.74 AU with NIRSPEC (on June 20). We detected 10 volatile species (H 2 O, OH * prompt emission, C 2 H 6 , CH 3 OH, H 2 CO, HCN, CO, CH 4 , NH 3 , and NH 2 ), and obtained upper limits for two others (C 2 H 2 and HDO). One-dimensional spatial profiles displayed different distributions for some volatiles, confirming either the existence of polar and apolar ices, or of chemically distinct active vents in the nucleus. The ortho-para ratio for water was 3.31 ± 0.33 (weighted mean of CRIRES and NIRSPEC results), implying a spin temperature >37 K at the 95% confidence limit. Our (3σ ) upper limit for HDO corresponds to D/H < 2.45 × 10 -3 (i.e., <16 Vienna Standard Mean Ocean Water, VSMOW). At R h = 1.2 AU (CRIRES), the production rate for water was Q(H 2 O) = 1.9 ± 0.1 × 10 29 s -1 and its rotational temperature was T rot ∼ 69 K. At R h = 0.75 AU (CSHELL), we measured Q(H 2 O) = 4.6 ± 0.6 × 10 29 s -1 and T rot = 80 K on March 31, and 6.6 ± 0.9 × 10 29 s -1 and T rot = 100 K on April 1. At R h = 1.74 AU (NIRSPEC), we obtained Q(H 2 O) = 1.1 ± 0.1 × 10 29 s -1 and T rot ∼ 50 K. The measured volatile abundance ratios classify comet C/2012 F6 as rather depleted in C 2 H 6 and CH 3 OH, while HCN, CH 4 , and CO displayed abundances close to their median values found among comets. H 2 CO was the only volatile showing a relative enhancement. The relative paucity of C 2 H 6 and CH 3 OH (with respect to H 2 O) suggests formation within warm regions of the nebula. However, the normal abundance of HCN and hypervolatiles CH 4 and CO, and the enhancement of H 2 CO, may indicate a possible heterogeneous nucleus of comet C/2012 F6 (Lemmon), possibly as a result of radial mixing within the protoplanetary disk.

Science, 2005

We quantified eight parent volatiles (H 2 O, C 2 H 6 , HCN, CO, CH 3 OH, H 2 CO, C 2 H 2 , and CH... more We quantified eight parent volatiles (H 2 O, C 2 H 6 , HCN, CO, CH 3 OH, H 2 CO, C 2 H 2 , and CH 4 ) in the Jupiter-family comet Tempel 1 using high-dispersion infrared spectroscopy in the wavelength range 2.8 to 5.0 micrometers. The abundance ratio for ethane was significantly higher after impact, whereas those for methanol and hydrogen cyanide were unchanged. The abundance ratios in the ejecta are similar to those for most Oort cloud comets, but methanol and acetylene are lower in Tempel 1 by a factor of about 2. These results suggest that the volatile ices in Tempel 1 and in most Oort cloud comets originated in a common region of the protoplanetary disk.

The Astrophysical Journal, 2011

The Planetary Science Journal, 2021

A major upgrade to the NIRSPEC instrument at the Keck II telescope was successfully completed in ... more A major upgrade to the NIRSPEC instrument at the Keck II telescope was successfully completed in time for near-infrared spectroscopic observations of comet 46P/Wirtanen during its exceptionally close flyby of Earth in 2018 December. These studies determined the abundances of several volatiles, including C2H2, C2H6, CH3OH, NH3, HCN, H2CO, and H2O. Long-slit spatial distributions of gas rotational temperature and column density are diagnostic for the presence of icy grains in the coma and understanding if different volatiles are associated with common or distinct outgassing sources. These spatial distributions suggest that C2H2, C2H6, and HCN have a common outgassing source, whereas H2O and CH3OH have additional, more extended sources. The synergy of these findings with observations by space missions (Rosetta and EPOXI) motivates continuing studies to address whether or not C2H6, C2H2, and HCN have a common source of release (plausibly associated with CO2) in a larger sample of comets...

The Astronomical Journal, 2020

The Astronomical Journal, 2019

The Astronomical Journal, 2017

The Astrophysical Journal, 2014

The Astrophysical Journal, 2005

The Astrophysical Journal, 2004

The Astrophysical Journal, 2008

The Astrophysical Journal, 2006

The Astrophysical Journal, 2007

The Astrophysical Journal, 2012

The Astrophysical Journal, 2008

The Astrophysical Journal, 2007

The Astrophysical Journal, 2006

The Astrophysical Journal, 2007

We present spatially resolved measurements of the rotational temperature and ortho-para ratio for... more We present spatially resolved measurements of the rotational temperature and ortho-para ratio for H 2 O in the inner coma of the Oort Cloud comet C/2004 Q2 (Machholz). Our results are based on direct simultaneous detections of ortho-H 2 O and para-H 2 O via "hot-band" fluorescence near 2.9 mm. We find a well-defined decline in rotational temperature with increasing nucleocentric distance (up to ∼1000 km). The ortho-para ratio remains constant (within stochastic uncertainty) with increasing nucleocentric distance and is close to the statistical equilibrium value of 3.0 ( [0.17], including, respectively, stochastic [systematic] uncertainty), resulting 2.86 ‫ע‬ 0.06 in spin temperature K. We compare the present results with those reported for other comets and discuss T ≥ 34 spin the difficulties in interpreting spin temperatures deduced from measured ortho-para ratios. Improved understanding of the special conditions that enable nuclear spin conversion would test the extent to which derived spin temperatures reflect the formative history or the processing record of cometary ices.

The Astrophysical Journal, 2013

The Astronomical Journal, 2013

We acquired near-infrared spectra of the Oort cloud comet C/2012 F6 (Lemmon) at three different h... more We acquired near-infrared spectra of the Oort cloud comet C/2012 F6 (Lemmon) at three different heliocentric distances (R h ) during the comet's 2013 perihelion passage, providing a comprehensive measure of the outgassing behavior of parent volatiles and cosmogonic indicators. Our observations were performed pre-perihelion at R h = 1.2 AU with CRIRES (on 2013 February 2 and 4), and post-perihelion at R h = 0.75 AU with CSHELL (on March 31 and April 1) and R h = 1.74 AU with NIRSPEC (on June 20). We detected 10 volatile species (H 2 O, OH * prompt emission, C 2 H 6 , CH 3 OH, H 2 CO, HCN, CO, CH 4 , NH 3 , and NH 2 ), and obtained upper limits for two others (C 2 H 2 and HDO). One-dimensional spatial profiles displayed different distributions for some volatiles, confirming either the existence of polar and apolar ices, or of chemically distinct active vents in the nucleus. The ortho-para ratio for water was 3.31 ± 0.33 (weighted mean of CRIRES and NIRSPEC results), implying a spin temperature >37 K at the 95% confidence limit. Our (3σ ) upper limit for HDO corresponds to D/H < 2.45 × 10 -3 (i.e., <16 Vienna Standard Mean Ocean Water, VSMOW). At R h = 1.2 AU (CRIRES), the production rate for water was Q(H 2 O) = 1.9 ± 0.1 × 10 29 s -1 and its rotational temperature was T rot ∼ 69 K. At R h = 0.75 AU (CSHELL), we measured Q(H 2 O) = 4.6 ± 0.6 × 10 29 s -1 and T rot = 80 K on March 31, and 6.6 ± 0.9 × 10 29 s -1 and T rot = 100 K on April 1. At R h = 1.74 AU (NIRSPEC), we obtained Q(H 2 O) = 1.1 ± 0.1 × 10 29 s -1 and T rot ∼ 50 K. The measured volatile abundance ratios classify comet C/2012 F6 as rather depleted in C 2 H 6 and CH 3 OH, while HCN, CH 4 , and CO displayed abundances close to their median values found among comets. H 2 CO was the only volatile showing a relative enhancement. The relative paucity of C 2 H 6 and CH 3 OH (with respect to H 2 O) suggests formation within warm regions of the nebula. However, the normal abundance of HCN and hypervolatiles CH 4 and CO, and the enhancement of H 2 CO, may indicate a possible heterogeneous nucleus of comet C/2012 F6 (Lemmon), possibly as a result of radial mixing within the protoplanetary disk.

Science, 2005

We quantified eight parent volatiles (H 2 O, C 2 H 6 , HCN, CO, CH 3 OH, H 2 CO, C 2 H 2 , and CH... more We quantified eight parent volatiles (H 2 O, C 2 H 6 , HCN, CO, CH 3 OH, H 2 CO, C 2 H 2 , and CH 4 ) in the Jupiter-family comet Tempel 1 using high-dispersion infrared spectroscopy in the wavelength range 2.8 to 5.0 micrometers. The abundance ratio for ethane was significantly higher after impact, whereas those for methanol and hydrogen cyanide were unchanged. The abundance ratios in the ejecta are similar to those for most Oort cloud comets, but methanol and acetylene are lower in Tempel 1 by a factor of about 2. These results suggest that the volatile ices in Tempel 1 and in most Oort cloud comets originated in a common region of the protoplanetary disk.

The Astrophysical Journal, 2011