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Jim Fuller - One of the best experts on this subject based on the ideXlab platform.
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the Spin Rate of pre collapse stellar cores wave driven angular momentum transport in massive stars
The Astrophysical Journal, 2015Co-Authors: Jim Fuller, Matteo Cantiello, Daniel Lecoanet, Eliot QuataertAbstract:The core rotation Rates of massive stars have a substantial impact on the nature of core-collapse (CC) supernovae and their compact remnants. We demonstRate that internal gravity waves (IGWs), excited via envelope convection during a red supergiant phase or during vigorous late time burning phases, can have a significant impact on the rotation Rate of the pre-SN core. In typical (10 M⊙ ≾ M ≾ 20 M⊙) supernova progenitors, IGWs may substantially Spin down the core, leading to iron core rotation periods P_(min,Fe) ≳ 30 s. Angular momentum (AM) conservation during the supernova would entail minimum NS rotation periods of P_(min,NS) ≳ 3 ms. In most cases, the combined effects of magnetic torques and IGW AM transport likely lead to substantially longer rotation periods. However, the stochastic influx of AM delivered by IGWs during shell burning phases inevitably Spin up a slowly rotating stellar core, leading to a maximum possible core rotation period. We estimate maximum iron core rotation periods of P_(max,Fe) ≾ 5 x 10^3 s in typical CC supernova progenitors, and a corresponding Spin period of P_(max,NS) ≾ 500 ms for newborn neutron stars (NSs). This is comparable to the typical birth Spin periods of most radio pulsars. Stochastic Spin-up via IGWs during shell O/Si burning may thus determine the initial rotation Rate of most NSs. For a given progenitor, this theory predicts a Maxwellian distribution in pre-collapse core rotation frequency that is uncorrelated with the Spin of the overlying envelope.
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the Spin Rate of pre collapse stellar cores wave driven angular momentum transport in massive stars
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: Jim Fuller, Matteo Cantiello, Daniel Lecoanet, Eliot QuataertAbstract:The core rotation Rates of massive stars have a substantial impact on the nature of core-collapse supernovae and their compact remnants. We demonstRate that internal gravity waves (IGW), excited via envelope convection during a red supergiant phase or during vigorous late time burning phases, can have a significant impact on the rotation Rate of the pre-SN core. In typical ($10 \, M_\odot \lesssim M \lesssim 20 \, M_\odot$) supernova progenitors, IGW may substantially Spin down the core, leading to iron core rotation periods $P_{\rm min,Fe} \gtrsim 30 \, {\rm s}$. Angular momentum (AM) conservation during the supernova would entail minimum NS rotation periods of $P_{\rm min,NS} \gtrsim 3 \, {\rm ms}$. In most cases, the combined effects of magnetic torques and IGW AM transport likely lead to substantially longer rotation periods. However, the stochastic influx of AM delivered by IGW during shell burning phases inevitably Spin up a slowly rotating stellar core, leading to a maximum possible core rotation period. We estimate maximum iron core rotation periods of $P_{\rm max,Fe} \lesssim 5 \times 10^3 \, {\rm s}$ in typical core-collapse supernova progenitors, and a corresponding Spin period of $P_{\rm max, NS} \lesssim 500 \, {\rm ms}$ for newborn neutron stars. This is comparable to the typical birth Spin periods of most radio pulsars. Stochastic Spin-up via IGW during shell O/Si burning may thus determine the initial rotation Rate of most neutron stars. For a given progenitor, this theory predicts a Maxwellian distribution in pre-collapse core rotation frequency that is uncorrelated with the Spin of the overlying envelope.
Ji Wang - One of the best experts on this subject based on the ideXlab platform.
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detecting water in the atmosphere of hr 8799 c with l band high dispersion spectroscopy aided by adaptive optics
The Astronomical Journal, 2018Co-Authors: Ji Wang, Dimitri Mawet, Jonathan J Fortney, Callie Hood, Caroline V Morley, Bjorn BennekeAbstract:High-dispersion spectroscopy of brown dwarfs and exoplanets enables exciting science cases, e.g., mapping surface inhomogeneity and measuring Spin Rate. Here, we present L-band observations of HR 8799 c using Keck NIRSPEC (R = 15,000) in adaptive optics (AO) mode (NIRSPAO). We search for molecular species (H_2O and CH_4) in the atmosphere of HR 8799 c with a template-matching method, which involves cross-correlation between reduced spectra and a template spectrum. We detect H_2O but not CH_4, which suggests disequilibrium chemistry in the atmosphere of HR 8799 c, and this is consistent with previous findings. We conduct planet signal injection simulations to estimate the sensitivity of our AO-aided high-dispersion spectroscopy observations. We conclude that 10^(−4) contrast can be reached in the L band. The sensitivity is mainly limited by the accuracy of line list used in modeling spectra and detector noise. The latter will be alleviated by the NIRSPEC upgrade.
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detecting water in the atmosphere of hr 8799 c with l band high dispersion spectroscopy aided by adaptive optics
arXiv: Earth and Planetary Astrophysics, 2018Co-Authors: Ji Wang, Dimitri Mawet, Jonathan J Fortney, Callie Hood, Caroline V Morley, Bjorn BennekeAbstract:High dispersion spectroscopy of brown dwarfs and exoplanets enables exciting science cases, e.g., mapping surface inhomogeneity and measuring Spin Rate. Here, we present $L$ band observations of HR 8799 c using Keck NIRSPEC (R=15,000) in adaptive optics (AO) mode (NIRSPAO). We search for molecular species (H$_2$O and CH$_4$) in the atmosphere of HR 8799 c with a template matching method, which involves cross correlation between reduced spectrum and a template spectrum. We detect H$_2$O but not CH$_4$, which suggests disequilibrium chemistry in the atmosphere of HR 8799 c, and this is consistent with previous findings. We conduct planet signal injection simulations to estimate the sensitivity of our AO-aided high dispersion spectroscopy observations. We conclude that $10^{-4}$ contrast can be reached in $L$ band. The sensitivity is mainly limited by the accuracy of line list used in modeling spectra and detector noise. The latter will be alleviated by the NIRSPEC upgrade.
Russ R Laher - One of the best experts on this subject based on the ideXlab platform.
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asteroid Spin Rate studies using large sky field surveys
Geoscience Letters, 2017Co-Authors: Chankao Chang, Hsingwen Lin, S R Kulkarni, David Levitan, Russ R Laher, Thomas A Prince, Jason SuraceAbstract:Eight campaigns to survey asteroid rotation periods have been carried out using the intermediate Palomar Transient Factory in the past 3 years. 2780 reliable rotation periods were obtained, from which we identified two new super-fast rotators (SFRs), (335433) 2005 UW163 and (40511) 1999 RE88, and 23 candidate SFRs. Along with other three known super-fast rotators, there are five known SFRs so far. Contrary to the case of rubble-pile asteroids (i.e., bounded aggregations by gravity only), an internal cohesion, ranging from 100 to 1000 Pa, is required to prevent these five SFRs from flying apart because of their super-fast rotations. This cohesion range is comparable with that of lunar regolith. However, some candidates of several kilometers in size require unusually high cohesion (i.e., a few thousands of Pa). Therefore, the confirmation of these kilometer-sized candidates can provide important information about asteroid interior structure. From the rotation periods we collected, we also found that the Spin-Rate limit of C-type asteroids, which has a lower bulk density, is lower than for S-type asteroids. This result is in agreement with the general picture of rubble-pile asteroids (i.e., lower bulk density, lower Spin-Rate limit). Moreover, the Spin-Rate distributions of asteroids of $$3< D < 15$$ km in size show a steady decrease along frequency for $$f > 5$$ rev/day, regardless of the location in the main belt. The YORP effect is indicated to be less efficient in altering asteroid Spin Rates from our results when compared with the flat distribution found by Pravec et al. (Icarus 197:497–504, 2008. doi: 10.1016/j.icarus.2008.05.012 ). We also found a significant number drop at f = 5 rev/day in the Spin-Rate distributions of asteroids of $$D < 3$$ km.
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asteroid light curves from the palomar transient factory survey rotation periods and phase functions from sparse photometry
The Astronomical Journal, 2015Co-Authors: A Waszczak, Chankao Chang, Yuchi Cheng, David Levitan, Russ R Laher, Jason Surace, E O Ofek, Frank J Masci, W H Ip, Daisuke KinoshitaAbstract:We fit 54,296 sparsely sampled asteroid light curves in the Palomar Transient Factory survey to a combined rotation plus phase-function model. Each light curve consists of 20 or more observations acquired in a single opposition. Using 805 asteroids in our sample that have reference periods in the literature, we find that the reliability of our fitted periods is a complicated function of the period, amplitude, apparent magnitude, and other light-curve attributes. Using the 805-asteroid ground-truth sample, we train an automated classifier to estimate (along with manual inspection) the validity of the remaining ~53,000 fitted periods. By this method we find that 9033 of our light curves (of ~8300 unique asteroids) have "reliable" periods. Subsequent consideration of asteroids with multiple light-curve fits indicates a 4% contamination in these "reliable" periods. For 3902 light curves with sufficient phase-angle coverage and either a reliable fit period or low amplitude, we examine the distribution of several phase-function parameters, none of which are bimodal though all correlate with the bond albedo and with visible-band colors. Comparing the theoretical maximal Spin Rate of a fluid body with our amplitude versus Spin-Rate distribution suggests that, if held together only by self-gravity, most asteroids are in general less dense than ~2 g cm^(−3), while C types have a lower limit of between 1 and 2 g cm^(−3). These results are in agreement with previous density estimates. For 5–20 km diameters, S types rotate faster and have lower amplitudes than C types. If both populations share the same angular momentum, this may indicate the two types' differing ability to deform under rotational stress. Lastly, we compare our absolute magnitudes (and apparent-magnitude residuals) to those of the Minor Planet Center's nominal (G = 0.15, rotation-neglecting) model; our phase-function plus Fourier-series fitting reduces asteroid photometric rms scatter by a factor of ~3.
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asteroid Spin Rate study using the intermediate palomar transient factory
Astrophysical Journal Supplement Series, 2015Co-Authors: Chankao Chang, Hsingwen Lin, Yuchi Cheng, Chowchoong Ngeow, Tingchang Yang, Adam Waszczak, S R Kulkarni, David Levitan, Branimir Sesar, Russ R LaherAbstract:Two dedicated asteroid rotation-period surveys have been carried out in the R band with ~20 minute cadence using the intermediate Palomar Transient Factory (iPTF) during 2014 January 6–9 and February 20–23. The total survey area covered 174 deg^2 in the ecliptic plane. Reliable rotation periods for 1438 asteroids are obtained from a larger data set of 6551 mostly main-belt asteroids, each with ⩾ 10 detections. Analysis of 1751, PTF-based, reliable rotation periods clearly shows the Spin barrier at ~2 hr for rubble-pile asteroids. We found a new large super-fast rotator, 2005 UW163, and another five candidates as well. For asteroids of 3 < D < 15 km, our Spin-Rate distribution shows a number decrease along with frequency after 5 rev day^(−1), which is consistent with the results of the Asteroid Light Curve Database. The discrepancy between our work and that of Pravec et al. (update 2014 April 20) comes mainly from asteroids with Δm < 0.2 mag, which could be the result of different survey stRategies. For asteroids with D < 3 km, we see a significant number drop at f = 6 rev day^(−1). The relatively short YORP effect timescale for small asteroids could have spun up those elongated objects to reach their Spin-Rate limit resulting in breakup to create such a number deficiency. We also see that the C-type asteroids show a smaller Spin-Rate limit than the S-type, which agrees with the general impression that C-type asteroids have a lower bulk density than S-type asteroids.
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asteroid Spin Rate study using the intermediate palomar transient factory
arXiv: Earth and Planetary Astrophysics, 2015Co-Authors: Chankao Chang, Hsingwen Lin, Yuchi Cheng, Chowchoong Ngeow, Tingchang Yang, Adam Waszczak, S R Kulkarni, David Levitan, Branimir Sesar, Russ R LaherAbstract:Two dedicated asteroid rotation-period surveys have been carried out using data taken on January 6-9 and February 20-23 of 2014 by the Intermediate Palomar Transient Factory (iPTF) in the $R$~band with $\sim 20$-min cadence. The total survey area covered 174~deg$^2$ in the ecliptic plane. Reliable rotation periods for 1,438 asteroids are obtained from a larger data set of 6,551 mostly main-belt asteroids, each with $\geq 10$~detections. Analysis of 1751, PTF based, reliable rotation periods clearly shows the "Spin barrier" at $\sim 2$~hours for "rubble-pile" asteroids. We also found a new large-sized super-fast rotator, 2005 UW163 (Chang et al., 2014), and other five candidates as well. Our Spin-Rate distributions of asteroids with $3 < D < 15$~km shows number decrease when frequency greater than 5 rev/day, which is consistent to that of the Asteroid Light Curve Database (LCDB, Warner et al., 2009) and the result of (Masiero et al., 2009). We found the discrepancy in the Spin-Rate distribution between our result and (Pravec et al., 2008, update 2014-04-20) is mainly from asteroids with $\Delta m < 0.2$ mag that might be primarily due to different survey stRategies. For asteroids with $D \leq 3$~km, we found a significant number drop at $f = 6$ rev/day. The YORP effect timescale for small-sized asteroid is shorter that makes more elongate objets spun up to reach their Spin-Rate limit and results in break-up. The K-S test suggests a possible difference in the Spin-Rate distributions of C- and S-type asteroids. We also find that C-type asteroids have a smaller Spin-Rate limit than the S-type, which agrees with the general sense that the C-type has lower bulk density than the S-type.
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asteroid lightcurves from the palomar transient factory survey rotation periods and phase functions from sparse photometry
arXiv: Earth and Planetary Astrophysics, 2015Co-Authors: Adam Waszczak, Chankao Chang, Yuchi Cheng, David Levitan, Russ R Laher, Jason Surace, E O Ofek, Frank J Masci, Daisuke Kinoshita, G HelouAbstract:We fit 54,296 sparsely-sampled asteroid lightcurves in the Palomar Transient Factory to a combined rotation plus phase-function model. Each lightcurve consists of 20+ observations acquired in a single opposition. Using 805 asteroids in our sample that have reference periods in the literature, we find the reliability of our fitted periods is a complicated function of the period, amplitude, apparent magnitude and other attributes. Using the 805-asteroid ground-truth sample, we train an automated classifier to estimate (along with manual inspection) the validity of the remaining 53,000 fitted periods. By this method we find 9,033 of our lightcurves (of 8,300 unique asteroids) have reliable periods. Subsequent consideration of asteroids with multiple lightcurve fits indicate 4% contamination in these reliable periods. For 3,902 lightcurves with sufficient phase-angle coverage and either a reliably-fit period or low amplitude, we examine the distribution of several phase-function parameters, none of which are bimodal though all correlate with the bond albedo and with visible-band colors. Comparing the theoretical maximal Spin Rate of a fluid body with our amplitude versus Spin-Rate distribution suggests that, if held together only by self-gravity, most asteroids are in general less dense than 2 g/cm$^3$, while C types have a lower limit of between 1 and 2 g/cm$^3$, in agreement with previous density estimates. For 5-20km diameters, S types rotate faster and have lower amplitudes than C types. If both populations share the same angular momentum, this may indicate the two types' differing ability to deform under rotational stress. Lastly, we compare our absolute magnitudes and apparent-magnitude residuals to those of the Minor Planet Center's nominal $G=0.15$, rotation-neglecting model; our phase-function plus Fourier-series fitting reduces asteroid photometric RMS scatter by a factor of 3.
Eliot Quataert - One of the best experts on this subject based on the ideXlab platform.
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the Spin Rate of pre collapse stellar cores wave driven angular momentum transport in massive stars
The Astrophysical Journal, 2015Co-Authors: Jim Fuller, Matteo Cantiello, Daniel Lecoanet, Eliot QuataertAbstract:The core rotation Rates of massive stars have a substantial impact on the nature of core-collapse (CC) supernovae and their compact remnants. We demonstRate that internal gravity waves (IGWs), excited via envelope convection during a red supergiant phase or during vigorous late time burning phases, can have a significant impact on the rotation Rate of the pre-SN core. In typical (10 M⊙ ≾ M ≾ 20 M⊙) supernova progenitors, IGWs may substantially Spin down the core, leading to iron core rotation periods P_(min,Fe) ≳ 30 s. Angular momentum (AM) conservation during the supernova would entail minimum NS rotation periods of P_(min,NS) ≳ 3 ms. In most cases, the combined effects of magnetic torques and IGW AM transport likely lead to substantially longer rotation periods. However, the stochastic influx of AM delivered by IGWs during shell burning phases inevitably Spin up a slowly rotating stellar core, leading to a maximum possible core rotation period. We estimate maximum iron core rotation periods of P_(max,Fe) ≾ 5 x 10^3 s in typical CC supernova progenitors, and a corresponding Spin period of P_(max,NS) ≾ 500 ms for newborn neutron stars (NSs). This is comparable to the typical birth Spin periods of most radio pulsars. Stochastic Spin-up via IGWs during shell O/Si burning may thus determine the initial rotation Rate of most NSs. For a given progenitor, this theory predicts a Maxwellian distribution in pre-collapse core rotation frequency that is uncorrelated with the Spin of the overlying envelope.
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the Spin Rate of pre collapse stellar cores wave driven angular momentum transport in massive stars
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: Jim Fuller, Matteo Cantiello, Daniel Lecoanet, Eliot QuataertAbstract:The core rotation Rates of massive stars have a substantial impact on the nature of core-collapse supernovae and their compact remnants. We demonstRate that internal gravity waves (IGW), excited via envelope convection during a red supergiant phase or during vigorous late time burning phases, can have a significant impact on the rotation Rate of the pre-SN core. In typical ($10 \, M_\odot \lesssim M \lesssim 20 \, M_\odot$) supernova progenitors, IGW may substantially Spin down the core, leading to iron core rotation periods $P_{\rm min,Fe} \gtrsim 30 \, {\rm s}$. Angular momentum (AM) conservation during the supernova would entail minimum NS rotation periods of $P_{\rm min,NS} \gtrsim 3 \, {\rm ms}$. In most cases, the combined effects of magnetic torques and IGW AM transport likely lead to substantially longer rotation periods. However, the stochastic influx of AM delivered by IGW during shell burning phases inevitably Spin up a slowly rotating stellar core, leading to a maximum possible core rotation period. We estimate maximum iron core rotation periods of $P_{\rm max,Fe} \lesssim 5 \times 10^3 \, {\rm s}$ in typical core-collapse supernova progenitors, and a corresponding Spin period of $P_{\rm max, NS} \lesssim 500 \, {\rm ms}$ for newborn neutron stars. This is comparable to the typical birth Spin periods of most radio pulsars. Stochastic Spin-up via IGW during shell O/Si burning may thus determine the initial rotation Rate of most neutron stars. For a given progenitor, this theory predicts a Maxwellian distribution in pre-collapse core rotation frequency that is uncorrelated with the Spin of the overlying envelope.
Chankao Chang - One of the best experts on this subject based on the ideXlab platform.
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asteroid Spin Rate studies using large sky field surveys
Geoscience Letters, 2017Co-Authors: Chankao Chang, Hsingwen Lin, S R Kulkarni, David Levitan, Russ R Laher, Thomas A Prince, Jason SuraceAbstract:Eight campaigns to survey asteroid rotation periods have been carried out using the intermediate Palomar Transient Factory in the past 3 years. 2780 reliable rotation periods were obtained, from which we identified two new super-fast rotators (SFRs), (335433) 2005 UW163 and (40511) 1999 RE88, and 23 candidate SFRs. Along with other three known super-fast rotators, there are five known SFRs so far. Contrary to the case of rubble-pile asteroids (i.e., bounded aggregations by gravity only), an internal cohesion, ranging from 100 to 1000 Pa, is required to prevent these five SFRs from flying apart because of their super-fast rotations. This cohesion range is comparable with that of lunar regolith. However, some candidates of several kilometers in size require unusually high cohesion (i.e., a few thousands of Pa). Therefore, the confirmation of these kilometer-sized candidates can provide important information about asteroid interior structure. From the rotation periods we collected, we also found that the Spin-Rate limit of C-type asteroids, which has a lower bulk density, is lower than for S-type asteroids. This result is in agreement with the general picture of rubble-pile asteroids (i.e., lower bulk density, lower Spin-Rate limit). Moreover, the Spin-Rate distributions of asteroids of $$3< D < 15$$ km in size show a steady decrease along frequency for $$f > 5$$ rev/day, regardless of the location in the main belt. The YORP effect is indicated to be less efficient in altering asteroid Spin Rates from our results when compared with the flat distribution found by Pravec et al. (Icarus 197:497–504, 2008. doi: 10.1016/j.icarus.2008.05.012 ). We also found a significant number drop at f = 5 rev/day in the Spin-Rate distributions of asteroids of $$D < 3$$ km.
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asteroid light curves from the palomar transient factory survey rotation periods and phase functions from sparse photometry
The Astronomical Journal, 2015Co-Authors: A Waszczak, Chankao Chang, Yuchi Cheng, David Levitan, Russ R Laher, Jason Surace, E O Ofek, Frank J Masci, W H Ip, Daisuke KinoshitaAbstract:We fit 54,296 sparsely sampled asteroid light curves in the Palomar Transient Factory survey to a combined rotation plus phase-function model. Each light curve consists of 20 or more observations acquired in a single opposition. Using 805 asteroids in our sample that have reference periods in the literature, we find that the reliability of our fitted periods is a complicated function of the period, amplitude, apparent magnitude, and other light-curve attributes. Using the 805-asteroid ground-truth sample, we train an automated classifier to estimate (along with manual inspection) the validity of the remaining ~53,000 fitted periods. By this method we find that 9033 of our light curves (of ~8300 unique asteroids) have "reliable" periods. Subsequent consideration of asteroids with multiple light-curve fits indicates a 4% contamination in these "reliable" periods. For 3902 light curves with sufficient phase-angle coverage and either a reliable fit period or low amplitude, we examine the distribution of several phase-function parameters, none of which are bimodal though all correlate with the bond albedo and with visible-band colors. Comparing the theoretical maximal Spin Rate of a fluid body with our amplitude versus Spin-Rate distribution suggests that, if held together only by self-gravity, most asteroids are in general less dense than ~2 g cm^(−3), while C types have a lower limit of between 1 and 2 g cm^(−3). These results are in agreement with previous density estimates. For 5–20 km diameters, S types rotate faster and have lower amplitudes than C types. If both populations share the same angular momentum, this may indicate the two types' differing ability to deform under rotational stress. Lastly, we compare our absolute magnitudes (and apparent-magnitude residuals) to those of the Minor Planet Center's nominal (G = 0.15, rotation-neglecting) model; our phase-function plus Fourier-series fitting reduces asteroid photometric rms scatter by a factor of ~3.
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asteroid Spin Rate study using the intermediate palomar transient factory
Astrophysical Journal Supplement Series, 2015Co-Authors: Chankao Chang, Hsingwen Lin, Yuchi Cheng, Chowchoong Ngeow, Tingchang Yang, Adam Waszczak, S R Kulkarni, David Levitan, Branimir Sesar, Russ R LaherAbstract:Two dedicated asteroid rotation-period surveys have been carried out in the R band with ~20 minute cadence using the intermediate Palomar Transient Factory (iPTF) during 2014 January 6–9 and February 20–23. The total survey area covered 174 deg^2 in the ecliptic plane. Reliable rotation periods for 1438 asteroids are obtained from a larger data set of 6551 mostly main-belt asteroids, each with ⩾ 10 detections. Analysis of 1751, PTF-based, reliable rotation periods clearly shows the Spin barrier at ~2 hr for rubble-pile asteroids. We found a new large super-fast rotator, 2005 UW163, and another five candidates as well. For asteroids of 3 < D < 15 km, our Spin-Rate distribution shows a number decrease along with frequency after 5 rev day^(−1), which is consistent with the results of the Asteroid Light Curve Database. The discrepancy between our work and that of Pravec et al. (update 2014 April 20) comes mainly from asteroids with Δm < 0.2 mag, which could be the result of different survey stRategies. For asteroids with D < 3 km, we see a significant number drop at f = 6 rev day^(−1). The relatively short YORP effect timescale for small asteroids could have spun up those elongated objects to reach their Spin-Rate limit resulting in breakup to create such a number deficiency. We also see that the C-type asteroids show a smaller Spin-Rate limit than the S-type, which agrees with the general impression that C-type asteroids have a lower bulk density than S-type asteroids.
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asteroid Spin Rate study using the intermediate palomar transient factory
arXiv: Earth and Planetary Astrophysics, 2015Co-Authors: Chankao Chang, Hsingwen Lin, Yuchi Cheng, Chowchoong Ngeow, Tingchang Yang, Adam Waszczak, S R Kulkarni, David Levitan, Branimir Sesar, Russ R LaherAbstract:Two dedicated asteroid rotation-period surveys have been carried out using data taken on January 6-9 and February 20-23 of 2014 by the Intermediate Palomar Transient Factory (iPTF) in the $R$~band with $\sim 20$-min cadence. The total survey area covered 174~deg$^2$ in the ecliptic plane. Reliable rotation periods for 1,438 asteroids are obtained from a larger data set of 6,551 mostly main-belt asteroids, each with $\geq 10$~detections. Analysis of 1751, PTF based, reliable rotation periods clearly shows the "Spin barrier" at $\sim 2$~hours for "rubble-pile" asteroids. We also found a new large-sized super-fast rotator, 2005 UW163 (Chang et al., 2014), and other five candidates as well. Our Spin-Rate distributions of asteroids with $3 < D < 15$~km shows number decrease when frequency greater than 5 rev/day, which is consistent to that of the Asteroid Light Curve Database (LCDB, Warner et al., 2009) and the result of (Masiero et al., 2009). We found the discrepancy in the Spin-Rate distribution between our result and (Pravec et al., 2008, update 2014-04-20) is mainly from asteroids with $\Delta m < 0.2$ mag that might be primarily due to different survey stRategies. For asteroids with $D \leq 3$~km, we found a significant number drop at $f = 6$ rev/day. The YORP effect timescale for small-sized asteroid is shorter that makes more elongate objets spun up to reach their Spin-Rate limit and results in break-up. The K-S test suggests a possible difference in the Spin-Rate distributions of C- and S-type asteroids. We also find that C-type asteroids have a smaller Spin-Rate limit than the S-type, which agrees with the general sense that the C-type has lower bulk density than the S-type.
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asteroid lightcurves from the palomar transient factory survey rotation periods and phase functions from sparse photometry
arXiv: Earth and Planetary Astrophysics, 2015Co-Authors: Adam Waszczak, Chankao Chang, Yuchi Cheng, David Levitan, Russ R Laher, Jason Surace, E O Ofek, Frank J Masci, Daisuke Kinoshita, G HelouAbstract:We fit 54,296 sparsely-sampled asteroid lightcurves in the Palomar Transient Factory to a combined rotation plus phase-function model. Each lightcurve consists of 20+ observations acquired in a single opposition. Using 805 asteroids in our sample that have reference periods in the literature, we find the reliability of our fitted periods is a complicated function of the period, amplitude, apparent magnitude and other attributes. Using the 805-asteroid ground-truth sample, we train an automated classifier to estimate (along with manual inspection) the validity of the remaining 53,000 fitted periods. By this method we find 9,033 of our lightcurves (of 8,300 unique asteroids) have reliable periods. Subsequent consideration of asteroids with multiple lightcurve fits indicate 4% contamination in these reliable periods. For 3,902 lightcurves with sufficient phase-angle coverage and either a reliably-fit period or low amplitude, we examine the distribution of several phase-function parameters, none of which are bimodal though all correlate with the bond albedo and with visible-band colors. Comparing the theoretical maximal Spin Rate of a fluid body with our amplitude versus Spin-Rate distribution suggests that, if held together only by self-gravity, most asteroids are in general less dense than 2 g/cm$^3$, while C types have a lower limit of between 1 and 2 g/cm$^3$, in agreement with previous density estimates. For 5-20km diameters, S types rotate faster and have lower amplitudes than C types. If both populations share the same angular momentum, this may indicate the two types' differing ability to deform under rotational stress. Lastly, we compare our absolute magnitudes and apparent-magnitude residuals to those of the Minor Planet Center's nominal $G=0.15$, rotation-neglecting model; our phase-function plus Fourier-series fitting reduces asteroid photometric RMS scatter by a factor of 3.