Symposium - International Astronomical Union, 2004
A model with two dust components is used do explain the circumstellar structure of weak-T Tauri s... more A model with two dust components is used do explain the circumstellar structure of weak-T Tauri stars. The IR-excess was calculated and compared to spectroscopic criteria in order to classify the objects according an evolutionary sequence. About 46% of the sample correspond to young main sequence stars showing dust distribution consistent with a disrupted disk, that could be possibly caused by the formation of a planetary system.
Proceedings of the International Astronomical Union, 2006
We have developed geometric disk models to study the circumstellar geometries by fitting the spec... more We have developed geometric disk models to study the circumstellar geometries by fitting the spectral energy distribution (SED) of T Tauri and Herbig Ae/Be stars. The simulations provide means to recognize the signatures of different disk structures, including the effects due to external UV photoevaporation.Following Chiang & Goldreich (1997) and Dullemond et al. (2001), we used hydrostatic, radiative equilibrium models for passive, reprocessing flared disks. The grains in the surface of the disk are directly exposed to the radiation from the star and the interior of the disk is heated by diffusion from the surface. Adopting this two-layers disk structure, our disk model was improved in order to optimize the parameters estimated by using a calculation technique based on genetic algorithms presented by Bentley & Corne (2002).In the present work, we apply the code to model the SED of protoplanetary disks, which have being destroyed by photoevaporation due to the presence of ionizing O...
A large sample of Herbig Ae/Be (HAeBe) candidates, distributed in different Galactic regions sout... more A large sample of Herbig Ae/Be (HAeBe) candidates, distributed in different Galactic regions south to declination +30 • , were identified by the Pico dos Dias Survey (a search for young stellar objects based on IRAS colors). Most of the candidates are nearby or associated with star-forming clouds, but several others are considered isolated objects. Aiming to verify the young nature of 93 HAeBe candidates, we searched for additional information that could be useful to confirm if they are pre-main-sequence (PMS) stars or evolved objects, which coincidentally show similar IRAS colors. By adopting a spectral index that is related to the amount of infrared excess and the shape of the spectral energy distribution, we have classified the sample according to three groups, which are analyzed on the basis of (1) circumstellar luminosity; (2) spatial distribution; (3) optical polarization; (4) nearinfrared colors; (5) stellar parameters (mass, age, effective temperature); and (5) intensity of emission lines. Our analysis indicates that only 76% of the studied sample, mainly the group with intermediate to low levels of circumstellar emission, can be more confidently considered PMS stars. The nature of the remaining stars, which are in the other group that contains the highest levels of infrared excess, remains to be confirmed. They share the same characteristics of evolved objects, requiring complementary studies in order to correctly classify them. At least seven objects show characteristics typical of post-asymptotic giant branch or proto-planetary nebulae.
Monthly Notices of the Royal Astronomical Society, 2008
A detailed study was performed for a sample of low-mass pre-main-sequence (PMS) stars, previously... more A detailed study was performed for a sample of low-mass pre-main-sequence (PMS) stars, previously identified as weak-line T Tauri stars, which are compared to members of the Tucanae and Horologium Associations. Aiming to verify if there is any pattern of abundances when comparing the young stars at different phases, we selected objects in the range from 1 to 100 Myr, which covers most of PMS evolution. High-resolution optical spectra were acquired at European Southern Observatory and Observatório do Pico dos Dias. The stellar fundamental parameters effective temperature and gravity were calculated by excitation and ionization equilibria of iron absorption lines. Chemical abundances were obtained via equivalent width calculations and spectral synthesis for 44 per cent of the sample, which shows metallicities within 0.5 dex solar. A classification was developed based on equivalent width of Li I 6708 Å and Hα lines and spectral types of the studied stars. This classification allowed a separation of the sample into categories that correspond to different evolutive stages in the PMS. The position of these stars in the Hertzsprung-Russell diagram was also inspected in order to estimate their ages and masses. Among the studied objects, it was verified that our sample actually contains seven weak-line T Tauri stars, three are Classical T Tauri, 12 are Fe/Ge PMS stars and 21 are post-T Tauri or young main-sequence stars. An estimation of circumstellar luminosity was obtained using a disc model to reproduce the observed spectral energy distribution. Most of the stars show low levels of circumstellar emission, corresponding to less than 30 per cent of the total emission.
Monthly Notices of the Royal Astronomical Society, 2002
We studied a sample of 27 T Tauri stars (TTs) showing a weak Hα line, selected from the Pico dos ... more We studied a sample of 27 T Tauri stars (TTs) showing a weak Hα line, selected from the Pico dos Dias Survey, a search for young stellar objects. A model to fit the spectral energy distribution is used in order to reproduce their observed infrared excess and to evaluate the individual contribution of the circumstellar components (dust disc and/or envelope) to the total emitted flux. The objects were separated into different categories of young stars, searching for an agreement with an evolutionary sequence. The classification is based on the stellar characteristics as spectral type; equivalent width of the Li 670.8-nm line; optical and X-ray properties; and infrared excess. We conclude that only 41 per cent of our sample actually correspond to weak TTs, and the remaining objects are mainly classical TTs or young mainsequence stars. Most of the stars have a near-infrared index typical of Class II objects and show an important fraction of the observed emission (∼30 per cent) being generated by the circumstellar material.
Monthly Notices of the Royal Astronomical Society, 2007
The protoplanetary discs of T Tauri and Herbig Ae/Be stars have been studied by using geometric d... more The protoplanetary discs of T Tauri and Herbig Ae/Be stars have been studied by using geometric disc models to fit their spectral energy distribution (SED). The simulations provide means to reproduce the signatures of different circumstellar structures, which are related to different levels of infrared excess. Aiming to improve our previous model that assumed a simple flat disc configuration, in the present work we adopt a reprocessing flared disc model that considers hydrostatic, radiative equilibrium (Dullemond et al. 2001). We developed a method to optimise the parameters estimation based on genetic algorithms (GA). This paper is dedicated to describe the implementation of the new code, which has been applied for Herbig stars from the Pico dos Dias Survey catalogue, in order to illustrate the quality of the fitting for a variety of SED shapes. The star AB Aur was used as a test of the GA parameters estimation, demonstrating that the new code reproduces successfully a canonical example of the flared disc model. The GA method gives good quality of fittings, but the range of input parameters must be chosen with caution, since unrealistic disc parameters can be derived. The flared disc model is confirmed to fit the flattened SEDs typical from Herbig stars, however the embedded objects (increasing SED slope) and debris discs (steeper SED) are not well fitted with this configuration. Even considering the limitation of the derived parameters, the automatic process of SED fitting provides an interesting tool for the statistical analysis of the circumstellar luminosity of large samples of young stars.
The ISM shock waves due to the collisions of a high velocity cloud (HVC) and the galactic disk ca... more The ISM shock waves due to the collisions of a high velocity cloud (HVC) and the galactic disk can generate turbulence and star formation processes. As a particular feature, a fraction of gas is ejected out of the disk, and this could be the origin of some molecular complexes like the Chamaeleon and rho Ophiuchi clouds. One can observe some hydrodynamical phases during the shock, when the cloud presents a coalescence stage, followed by re-expansion and deep disk penetration. We present results of evolving shocks done by 3D hydrodynamical simulations of a falling high velocity cloud on the galactic disk with conditions more realistic than preceding studies, with equations which include molecular cooling.
Context. A sample of 27 sources, cataloged as pre-main sequence stars by the Pico dos Dias Survey... more Context. A sample of 27 sources, cataloged as pre-main sequence stars by the Pico dos Dias Survey (PDS), is analyzed to investigate a possible contamination by post-AGB stars. The far-infrared excess due to dust present in the circumstellar envelope is typical of both categories: young stars and objects that have already left the main sequence and are suffering severe mass loss. Aims. The two known post-AGB stars in our sample inspired us to seek for other very likely or possible post-AGB objects among PDS sources previously suggested to be Herbig Ae/Be stars, by revisiting the observational database of this sample. Methods. In a comparative study with well known post-AGBs, several characteristics were evaluated: (i) parameters related to the circumstellar emission; (ii) spatial distribution to verify the background contribution from dark clouds; (iii) spectral features; and (iv) optical and infrared colors. Results. These characteristics suggest that seven objects of the studied sample are very likely post-AGBs, five are possible post-AGBs, eight are unlikely post-AGBs, and the nature of seven objects remains unclear.
ABSTRACT We propose a number of methods to produce 3D simulations of the gas density distribution... more ABSTRACT We propose a number of methods to produce 3D simulations of the gas density distribution of molecular clouds. The methods make use of random number generation and of simple recursive construction rules dependent on a few parameters. A large number of simulations were produced by varying the parameters of these rules. The projected 2D images of the simulated clouds were compared to those of observed molecular clouds. The quantitative description of a simulation is approached via the fractal dimension D and the factor/f of the contour levels of the images, obtained from the relation (area) exp 1/2 = K x (perimeter) exp 1/D. From our measurements of the fractal dimension of the visual extinction contours of clouds of the Chamaeleon complex and from other results in the literature, D and K are found to be in the range 1.21-1.52 and 0.32-0.45, respectively. The simulated clouds that we obtained with D in the correct range were submitted to additional tests like the study of the normalized-mass vs normalized-radius relation, visual inspection of a perspective representation of the density distribution, and a study of the projected distribution of density peaks. The tests show that the simulated clouds have statistical properties similar to that observed ones. Theoretical reasons for D being in the interval 1.2-1.5 are discussed. Some examples of possible applications of our simulations are briefly discussed.
Este trabalho está diretamente relacionado ao desenvolvimento do altímetro laser para a missão AS... more Este trabalho está diretamente relacionado ao desenvolvimento do altímetro laser para a missão ASTER, denominado ALR. A primeira missão brasileira ao espaço profundo planeja enviar em 2017 uma nave para explorar o asteroide triplo 2001-SN263. O ALR será utilizado na investigação científica da forma, topografia e distribuição de massa dos componentes do asteroide triplo, que será realizada nas fases de maior proximidade. O instrumento desempenhará também papel importante como sensor auxiliar de navegação da nave. Coordenado pela UFABC, o desenvolvimento proposto envolve uma parceria entre a UFABC, UNICAMP e empresas do setor aeroespacial nacional. Este trabalho descreve as modelagens e simulações efetuadas para criação e testes do software que comporá a unidade de controle e processamento de sinais do instrumento. Como resultado principal, um ambiente de simulação da operação do aparelho foi criado e denominado ALR_Sim. A simulação envolve as características: do aparelho (emissor e receptor) e do ambiente em que ele opera (meio e alvo: transmissividade, refletividade, rugosidade, ocorrência de falésia, superfícies inclinadas, etc.). Como saída da simulação, as formas de onda que se espera obter como sinal de retorno para diferentes formas de pulsos emitidos. O ALR_Sim foi testado com sucesso com relação às situações mais comuns esperadas.
The Brazilian deep space mission ASTER, as temporarily named, plans to send a small spacecraft to... more The Brazilian deep space mission ASTER, as temporarily named, plans to send a small spacecraft to encounter and investigate the triple asteroid 2001-SN263. The launch is scheduled (initially) to occur in 2015, arriving in 2018. The main motivation of the mission is the development of technology and expertise to leverage the national space sector. Within the scientific goals, the investigation of the still unknown asteroid 2001-SN263. The main project guideline is to aggregate the widest possible Brazilian involvement in the platform, the development and operation of subsystems, integration, payload, as well as in the tracking, navigation, guidance and control of the probe. To meet this guideline, among others, the decision for the development of a laser altimeter in Brazil to fly in the mission was taken. This effort is currently coordinated by a group of researchers from the aerospace engineering personnel of UFABC. This article presents the preliminary development plan for the design of this instrument, which was called ALR (ASTER Laser Rangefinder).
Fractal statistics in young star clusters: structural parameters and dynamical evolution
Monthly Notices of the Royal Astronomical Society, 2019
We used fractal statistics to quantify the degree of observed substructures in a sample of 50 emb... more We used fractal statistics to quantify the degree of observed substructures in a sample of 50 embedded clusters and more evolved open clusters (< 100 Myr) found in different galactic regions. The observed fractal parameters were compared with N-body simulations from the literature, which reproduce star-forming regions under different initial conditions and geometries that are related to the cluster's dynamical evolution. Parallax and proper motion from Gaia-DR2 were used to accurately determine cluster membership by using the Bayesian model and cross-entropy technique. The statistical parameters $\mathcal {Q}$, $\overline{m}$ and $\overline{s}$ were used to compare observed cluster structure with simulations. A low level of substructures ($\mathcal {Q} \lt $ 0.8) is found for most of the sample that coincides with simulations of regions showing fractal dimension D ∼ 2–3. Few clusters (<20 per cent) have uniform distribution with a radial density profile (α < 2). A compa...
large-scale structure of the universe In this work, we analyse the temperature fluctuations of th... more large-scale structure of the universe In this work, we analyse the temperature fluctuations of the cosmic microwave background radiation observed by COBE and show that the distribution can be fitted by a fractal distribution with a fractal dimension D=1.43±0.07. This value is in close agreement with the fractal dimension obtained by Coleman and Pietronero (1992) and Luo and Schramm (1992) from galaxy-galaxy and cluster-cluster correlations up to ~100 h-1 Mpc. The fact that the observed temperature fluctuations correspond to scales much larger than 100 h-1 Mpc and are signatures of the primordial density fluctuations at the recombination layer suggests that the structure of the matter at the early universe was already fractal and thus non-homogeneous on those scales. This result may have important consequences for the theoretical framework that describes the universe
This paper presents an analytical model to determine the wind turbine capacity factor from wind a... more This paper presents an analytical model to determine the wind turbine capacity factor from wind and turbine characteristics. This model was validated by experimental results. The proposed model was used to identify analytically the effect of the nominal turbine velocity choice on the capacity factor for different wind conditions. Resumo: Este artigo apresenta um modelo analítico para determinar o fator de capacidade da turbina eólica a partir das características do vento e da turbina. Este modelo foi validado por resultados experimentais. O modelo proposto foi utilizado para identificar analiticamente o efeito da escolha da velocidade nominal da turbina no fator de capacidade para diferentes condições de vento.
Context. The relationship between young stellar clusters and their respective parental molecular ... more Context. The relationship between young stellar clusters and their respective parental molecular clouds remains an open issue. Recent inquiries consider the similarities between substructures of clouds and clusters and whether they are a coincidence or, rather, an indication of a physical relationship. To address these issues, we studied the CMa OB1/R1 region, which shows evidence of a complex star formation history. Aims. We obtained molecular cloud mapping with the IRAM-30 metre telescope to reveal the physical conditions of an unexplored side of the CMa region with the aim of comparing the morphology of the clouds to the distribution of young stellar objects (YSOs). We also studied the cloud kinematics in pursuit of gradients and jet signatures that could trace different star formation scenarios. Methods. The YSOs were selected on the basis of astrometric data from Gaia EDR3 that characterize the moving groups. The distance of 1099−24+25 pc was obtained for the sample, based on t...
Symposium - International Astronomical Union, 2004
A model with two dust components is used do explain the circumstellar structure of weak-T Tauri s... more A model with two dust components is used do explain the circumstellar structure of weak-T Tauri stars. The IR-excess was calculated and compared to spectroscopic criteria in order to classify the objects according an evolutionary sequence. About 46% of the sample correspond to young main sequence stars showing dust distribution consistent with a disrupted disk, that could be possibly caused by the formation of a planetary system.
Proceedings of the International Astronomical Union, 2006
We have developed geometric disk models to study the circumstellar geometries by fitting the spec... more We have developed geometric disk models to study the circumstellar geometries by fitting the spectral energy distribution (SED) of T Tauri and Herbig Ae/Be stars. The simulations provide means to recognize the signatures of different disk structures, including the effects due to external UV photoevaporation.Following Chiang & Goldreich (1997) and Dullemond et al. (2001), we used hydrostatic, radiative equilibrium models for passive, reprocessing flared disks. The grains in the surface of the disk are directly exposed to the radiation from the star and the interior of the disk is heated by diffusion from the surface. Adopting this two-layers disk structure, our disk model was improved in order to optimize the parameters estimated by using a calculation technique based on genetic algorithms presented by Bentley & Corne (2002).In the present work, we apply the code to model the SED of protoplanetary disks, which have being destroyed by photoevaporation due to the presence of ionizing O...
A large sample of Herbig Ae/Be (HAeBe) candidates, distributed in different Galactic regions sout... more A large sample of Herbig Ae/Be (HAeBe) candidates, distributed in different Galactic regions south to declination +30 • , were identified by the Pico dos Dias Survey (a search for young stellar objects based on IRAS colors). Most of the candidates are nearby or associated with star-forming clouds, but several others are considered isolated objects. Aiming to verify the young nature of 93 HAeBe candidates, we searched for additional information that could be useful to confirm if they are pre-main-sequence (PMS) stars or evolved objects, which coincidentally show similar IRAS colors. By adopting a spectral index that is related to the amount of infrared excess and the shape of the spectral energy distribution, we have classified the sample according to three groups, which are analyzed on the basis of (1) circumstellar luminosity; (2) spatial distribution; (3) optical polarization; (4) nearinfrared colors; (5) stellar parameters (mass, age, effective temperature); and (5) intensity of emission lines. Our analysis indicates that only 76% of the studied sample, mainly the group with intermediate to low levels of circumstellar emission, can be more confidently considered PMS stars. The nature of the remaining stars, which are in the other group that contains the highest levels of infrared excess, remains to be confirmed. They share the same characteristics of evolved objects, requiring complementary studies in order to correctly classify them. At least seven objects show characteristics typical of post-asymptotic giant branch or proto-planetary nebulae.
Monthly Notices of the Royal Astronomical Society, 2008
A detailed study was performed for a sample of low-mass pre-main-sequence (PMS) stars, previously... more A detailed study was performed for a sample of low-mass pre-main-sequence (PMS) stars, previously identified as weak-line T Tauri stars, which are compared to members of the Tucanae and Horologium Associations. Aiming to verify if there is any pattern of abundances when comparing the young stars at different phases, we selected objects in the range from 1 to 100 Myr, which covers most of PMS evolution. High-resolution optical spectra were acquired at European Southern Observatory and Observatório do Pico dos Dias. The stellar fundamental parameters effective temperature and gravity were calculated by excitation and ionization equilibria of iron absorption lines. Chemical abundances were obtained via equivalent width calculations and spectral synthesis for 44 per cent of the sample, which shows metallicities within 0.5 dex solar. A classification was developed based on equivalent width of Li I 6708 Å and Hα lines and spectral types of the studied stars. This classification allowed a separation of the sample into categories that correspond to different evolutive stages in the PMS. The position of these stars in the Hertzsprung-Russell diagram was also inspected in order to estimate their ages and masses. Among the studied objects, it was verified that our sample actually contains seven weak-line T Tauri stars, three are Classical T Tauri, 12 are Fe/Ge PMS stars and 21 are post-T Tauri or young main-sequence stars. An estimation of circumstellar luminosity was obtained using a disc model to reproduce the observed spectral energy distribution. Most of the stars show low levels of circumstellar emission, corresponding to less than 30 per cent of the total emission.
Monthly Notices of the Royal Astronomical Society, 2002
We studied a sample of 27 T Tauri stars (TTs) showing a weak Hα line, selected from the Pico dos ... more We studied a sample of 27 T Tauri stars (TTs) showing a weak Hα line, selected from the Pico dos Dias Survey, a search for young stellar objects. A model to fit the spectral energy distribution is used in order to reproduce their observed infrared excess and to evaluate the individual contribution of the circumstellar components (dust disc and/or envelope) to the total emitted flux. The objects were separated into different categories of young stars, searching for an agreement with an evolutionary sequence. The classification is based on the stellar characteristics as spectral type; equivalent width of the Li 670.8-nm line; optical and X-ray properties; and infrared excess. We conclude that only 41 per cent of our sample actually correspond to weak TTs, and the remaining objects are mainly classical TTs or young mainsequence stars. Most of the stars have a near-infrared index typical of Class II objects and show an important fraction of the observed emission (∼30 per cent) being generated by the circumstellar material.
Monthly Notices of the Royal Astronomical Society, 2007
The protoplanetary discs of T Tauri and Herbig Ae/Be stars have been studied by using geometric d... more The protoplanetary discs of T Tauri and Herbig Ae/Be stars have been studied by using geometric disc models to fit their spectral energy distribution (SED). The simulations provide means to reproduce the signatures of different circumstellar structures, which are related to different levels of infrared excess. Aiming to improve our previous model that assumed a simple flat disc configuration, in the present work we adopt a reprocessing flared disc model that considers hydrostatic, radiative equilibrium (Dullemond et al. 2001). We developed a method to optimise the parameters estimation based on genetic algorithms (GA). This paper is dedicated to describe the implementation of the new code, which has been applied for Herbig stars from the Pico dos Dias Survey catalogue, in order to illustrate the quality of the fitting for a variety of SED shapes. The star AB Aur was used as a test of the GA parameters estimation, demonstrating that the new code reproduces successfully a canonical example of the flared disc model. The GA method gives good quality of fittings, but the range of input parameters must be chosen with caution, since unrealistic disc parameters can be derived. The flared disc model is confirmed to fit the flattened SEDs typical from Herbig stars, however the embedded objects (increasing SED slope) and debris discs (steeper SED) are not well fitted with this configuration. Even considering the limitation of the derived parameters, the automatic process of SED fitting provides an interesting tool for the statistical analysis of the circumstellar luminosity of large samples of young stars.
The ISM shock waves due to the collisions of a high velocity cloud (HVC) and the galactic disk ca... more The ISM shock waves due to the collisions of a high velocity cloud (HVC) and the galactic disk can generate turbulence and star formation processes. As a particular feature, a fraction of gas is ejected out of the disk, and this could be the origin of some molecular complexes like the Chamaeleon and rho Ophiuchi clouds. One can observe some hydrodynamical phases during the shock, when the cloud presents a coalescence stage, followed by re-expansion and deep disk penetration. We present results of evolving shocks done by 3D hydrodynamical simulations of a falling high velocity cloud on the galactic disk with conditions more realistic than preceding studies, with equations which include molecular cooling.
Context. A sample of 27 sources, cataloged as pre-main sequence stars by the Pico dos Dias Survey... more Context. A sample of 27 sources, cataloged as pre-main sequence stars by the Pico dos Dias Survey (PDS), is analyzed to investigate a possible contamination by post-AGB stars. The far-infrared excess due to dust present in the circumstellar envelope is typical of both categories: young stars and objects that have already left the main sequence and are suffering severe mass loss. Aims. The two known post-AGB stars in our sample inspired us to seek for other very likely or possible post-AGB objects among PDS sources previously suggested to be Herbig Ae/Be stars, by revisiting the observational database of this sample. Methods. In a comparative study with well known post-AGBs, several characteristics were evaluated: (i) parameters related to the circumstellar emission; (ii) spatial distribution to verify the background contribution from dark clouds; (iii) spectral features; and (iv) optical and infrared colors. Results. These characteristics suggest that seven objects of the studied sample are very likely post-AGBs, five are possible post-AGBs, eight are unlikely post-AGBs, and the nature of seven objects remains unclear.
ABSTRACT We propose a number of methods to produce 3D simulations of the gas density distribution... more ABSTRACT We propose a number of methods to produce 3D simulations of the gas density distribution of molecular clouds. The methods make use of random number generation and of simple recursive construction rules dependent on a few parameters. A large number of simulations were produced by varying the parameters of these rules. The projected 2D images of the simulated clouds were compared to those of observed molecular clouds. The quantitative description of a simulation is approached via the fractal dimension D and the factor/f of the contour levels of the images, obtained from the relation (area) exp 1/2 = K x (perimeter) exp 1/D. From our measurements of the fractal dimension of the visual extinction contours of clouds of the Chamaeleon complex and from other results in the literature, D and K are found to be in the range 1.21-1.52 and 0.32-0.45, respectively. The simulated clouds that we obtained with D in the correct range were submitted to additional tests like the study of the normalized-mass vs normalized-radius relation, visual inspection of a perspective representation of the density distribution, and a study of the projected distribution of density peaks. The tests show that the simulated clouds have statistical properties similar to that observed ones. Theoretical reasons for D being in the interval 1.2-1.5 are discussed. Some examples of possible applications of our simulations are briefly discussed.
Este trabalho está diretamente relacionado ao desenvolvimento do altímetro laser para a missão AS... more Este trabalho está diretamente relacionado ao desenvolvimento do altímetro laser para a missão ASTER, denominado ALR. A primeira missão brasileira ao espaço profundo planeja enviar em 2017 uma nave para explorar o asteroide triplo 2001-SN263. O ALR será utilizado na investigação científica da forma, topografia e distribuição de massa dos componentes do asteroide triplo, que será realizada nas fases de maior proximidade. O instrumento desempenhará também papel importante como sensor auxiliar de navegação da nave. Coordenado pela UFABC, o desenvolvimento proposto envolve uma parceria entre a UFABC, UNICAMP e empresas do setor aeroespacial nacional. Este trabalho descreve as modelagens e simulações efetuadas para criação e testes do software que comporá a unidade de controle e processamento de sinais do instrumento. Como resultado principal, um ambiente de simulação da operação do aparelho foi criado e denominado ALR_Sim. A simulação envolve as características: do aparelho (emissor e receptor) e do ambiente em que ele opera (meio e alvo: transmissividade, refletividade, rugosidade, ocorrência de falésia, superfícies inclinadas, etc.). Como saída da simulação, as formas de onda que se espera obter como sinal de retorno para diferentes formas de pulsos emitidos. O ALR_Sim foi testado com sucesso com relação às situações mais comuns esperadas.
The Brazilian deep space mission ASTER, as temporarily named, plans to send a small spacecraft to... more The Brazilian deep space mission ASTER, as temporarily named, plans to send a small spacecraft to encounter and investigate the triple asteroid 2001-SN263. The launch is scheduled (initially) to occur in 2015, arriving in 2018. The main motivation of the mission is the development of technology and expertise to leverage the national space sector. Within the scientific goals, the investigation of the still unknown asteroid 2001-SN263. The main project guideline is to aggregate the widest possible Brazilian involvement in the platform, the development and operation of subsystems, integration, payload, as well as in the tracking, navigation, guidance and control of the probe. To meet this guideline, among others, the decision for the development of a laser altimeter in Brazil to fly in the mission was taken. This effort is currently coordinated by a group of researchers from the aerospace engineering personnel of UFABC. This article presents the preliminary development plan for the design of this instrument, which was called ALR (ASTER Laser Rangefinder).
Fractal statistics in young star clusters: structural parameters and dynamical evolution
Monthly Notices of the Royal Astronomical Society, 2019
We used fractal statistics to quantify the degree of observed substructures in a sample of 50 emb... more We used fractal statistics to quantify the degree of observed substructures in a sample of 50 embedded clusters and more evolved open clusters (< 100 Myr) found in different galactic regions. The observed fractal parameters were compared with N-body simulations from the literature, which reproduce star-forming regions under different initial conditions and geometries that are related to the cluster's dynamical evolution. Parallax and proper motion from Gaia-DR2 were used to accurately determine cluster membership by using the Bayesian model and cross-entropy technique. The statistical parameters $\mathcal {Q}$, $\overline{m}$ and $\overline{s}$ were used to compare observed cluster structure with simulations. A low level of substructures ($\mathcal {Q} \lt $ 0.8) is found for most of the sample that coincides with simulations of regions showing fractal dimension D ∼ 2–3. Few clusters (<20 per cent) have uniform distribution with a radial density profile (α < 2). A compa...
large-scale structure of the universe In this work, we analyse the temperature fluctuations of th... more large-scale structure of the universe In this work, we analyse the temperature fluctuations of the cosmic microwave background radiation observed by COBE and show that the distribution can be fitted by a fractal distribution with a fractal dimension D=1.43±0.07. This value is in close agreement with the fractal dimension obtained by Coleman and Pietronero (1992) and Luo and Schramm (1992) from galaxy-galaxy and cluster-cluster correlations up to ~100 h-1 Mpc. The fact that the observed temperature fluctuations correspond to scales much larger than 100 h-1 Mpc and are signatures of the primordial density fluctuations at the recombination layer suggests that the structure of the matter at the early universe was already fractal and thus non-homogeneous on those scales. This result may have important consequences for the theoretical framework that describes the universe
This paper presents an analytical model to determine the wind turbine capacity factor from wind a... more This paper presents an analytical model to determine the wind turbine capacity factor from wind and turbine characteristics. This model was validated by experimental results. The proposed model was used to identify analytically the effect of the nominal turbine velocity choice on the capacity factor for different wind conditions. Resumo: Este artigo apresenta um modelo analítico para determinar o fator de capacidade da turbina eólica a partir das características do vento e da turbina. Este modelo foi validado por resultados experimentais. O modelo proposto foi utilizado para identificar analiticamente o efeito da escolha da velocidade nominal da turbina no fator de capacidade para diferentes condições de vento.
Context. The relationship between young stellar clusters and their respective parental molecular ... more Context. The relationship between young stellar clusters and their respective parental molecular clouds remains an open issue. Recent inquiries consider the similarities between substructures of clouds and clusters and whether they are a coincidence or, rather, an indication of a physical relationship. To address these issues, we studied the CMa OB1/R1 region, which shows evidence of a complex star formation history. Aims. We obtained molecular cloud mapping with the IRAM-30 metre telescope to reveal the physical conditions of an unexplored side of the CMa region with the aim of comparing the morphology of the clouds to the distribution of young stellar objects (YSOs). We also studied the cloud kinematics in pursuit of gradients and jet signatures that could trace different star formation scenarios. Methods. The YSOs were selected on the basis of astrometric data from Gaia EDR3 that characterize the moving groups. The distance of 1099−24+25 pc was obtained for the sample, based on t...
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