We report on our radial velocity monitoring project of a wide range of evolved stars where binari... more We report on our radial velocity monitoring project of a wide range of evolved stars where binarity was proposed to explain some of their peculiarities. Our spectrograph HERMES is a new optical echelle spectrograph mounted on the 1.2m Mercator telescope on La Palma, built by a consortium of Belgian Institutes (KULeuven, ULB, Royal Observatory) with contributions from the Geneva Observatory and Landessternwarte Tautenburg. By combining high S/N single observations with low S/N time-series, we aim at quantifying the orbital and chemical characteristics of every distinct subgroup. The final goal is to gain insight in the diverse binary interaction processes relevant at late stages of stellar evolution. We discuss our project, the unique capabilities of HERMES, and present the first results of our program.
Proceedings of the International Astronomical Union
To investigate the binary hypothesis in the formation of planetary nebulae, we have been doing lo... more To investigate the binary hypothesis in the formation of planetary nebulae, we have been doing long-term photometry and radial velocity (RV) monitoring of bright post-AGB stars which possess bipolar or ellipsoidal nebulae but no indication of a disk in their spectral energy distribution, indicative of a binary companion. RV’s are determined by cross correlating high-resolution spectra with a line mask. Stellar variability and companions both deform the cross correlation function (CCF) and induce periodic variations in the RV. To uniformly quantify the asymmetry of the CCF from a Gaussian, we propose to fit the CCF profile with a Gauss-Hermite series and determine all CCF parameters (RV, skewness, FWHM, and depth) in one single fit. We analyze the correlation and time series of these CCF parameters for V448 Lac and conclude that its RV variability is most likely due to stellar pulsation and not to an orbiting body.
Context. Hundreds of candidate hybrid pulsators of intermediate type A–F were revealed by recent ... more Context. Hundreds of candidate hybrid pulsators of intermediate type A–F were revealed by recent space missions. Hybrid pulsators allow us to study the full stellar interiors, where both low-order p- and high-order g-modes are simultaneously excited. The true hybrid stars must be identified since other processes, related to stellar multiplicity or rotation, might explain the presence of (some) low frequencies observed in their periodograms. Aims. We measured the radial velocities of 50 candidate δ Scuti −γ Doradus hybrid stars from the Kepler mission with the Hermes and ace spectrographs over a time span of months to years. We aim to derive the fraction of binary and multiple systems and to provide an independent and homogeneous determination of the atmospheric properties and v sin i for all targets. The long(er)-term objective is to identify the (probable) physical cause of the low frequencies. Methods. We computed one-dimensional cross-correlation functions (CCFs) in order to find...
Proceedings of the International Astronomical Union
V4334 Sgr (a.k.a. Sakurai's object) is the central star of an old planetary nebula that under... more V4334 Sgr (a.k.a. Sakurai's object) is the central star of an old planetary nebula that underwent a very late thermal pulse a few years before its discovery in 1996. We have been monitoring the evolution of the optical emission line spectrum since 2001. The goal is to improve the evolutionary models by constraining them with the temporal evolution of the central star temperature. In addition the high resolution spectral observations obtained by X-shooter and ALMA show the temporal evolution of the different morphological components.
While in the past spherodicity was assumed, and still is used in modeling of most nebulae, we kno... more While in the past spherodicity was assumed, and still is used in modeling of most nebulae, we know now that only a small number of planetary nebulae (PNe) are really spherical or at least nearly round. Round planetary nebulae are the minority of objects. In the case of those objects that underwent a very late helium flash (called VLTP objects
While in the past spheroidicity was assumed, and still is used in modeling of most nebulae, we kn... more While in the past spheroidicity was assumed, and still is used in modeling of most nebulae, we know now that only a small number of planetary nebulae (PNe) are really spherical or at least nearly round. Round planetary nebulae are the minority of objects. In case of those objects that underwent a very late helium flash (called VLTP or "born-again" PNe) it seems to be different. The first, hydrogen rich PN, is more or less round. The ejecta from the VLTP event is extremely asymmetrically. Angular momentum is mostly assumed to be the main reason for the asymmetry in PNe. Thus we have to find processes either changing their behavior within a few hundred to a few thousands of years or change their properties dramatically due to the variation of the abundance. They most likely have a strong link or dependency with the abundance of the ejecta.
While in the past spheroidicity was assumed, and still is used in modeling of most nebulae, we kn... more While in the past spheroidicity was assumed, and still is used in modeling of most nebulae, we know now that only a small number of planetary nebulae (PNe) are really spherical or at least nearly round. Round planetary nebulae are the minority of objects. In case of those objects that underwent a very late helium flash (called VLTP or "born-again" PNe) it seems to be different. The first, hydrogen rich PN, is more or less round. The ejecta from the VLTP event is extremely asymmetrically. Angular momentum is mostly assumed to be the main reason for the asymmetry in PNe. Thus we have to find processes either changing their behavior within a few hundred to a few thousands of years or change their properties dramatically due to the variation of the abundance. They most likely have a strong link or dependency with the abundance of the ejecta.
The results from a Hubble Space T elescope (HST) snapshot survey of post-AGB objects are shown. T... more The results from a Hubble Space T elescope (HST) snapshot survey of post-AGB objects are shown. The aim of the survey is to complement existing HST images of PPN and to connect various types of nebulosities with physical and chemical properties of their central stars. Nebulosities are detected in 15 of 33 sources. Images and photometric and geometric measurements are presented. For sources with nebulosities we see a morphological bifurcation into two groups, DUPLEX and SOLE, as previous studies have found. We find further support to the previous results suggesting that this dichotomy is caused by a difference in optical thickness of the dust shell. The remaining 18 sources are classified as stellar post-AGB objects, because our observations indicate a lack of nebulosity. We show that some stellar sources may in fact be DUPLEX or SOLE based on their infrared colors. The cause of the differences among the groups are investigated. We discuss some evidence suggesting that high progenitor-mass AGB stars tend to become DUPLEX post-AGB objects. Intermediate progenitormass AGB stars tend to be SOLE post-AGB objects. Most of the stellar sources probably have low mass progenitors and do not seem to develop nebulosities during the post-AGB phase and therefore do not become planetary nebulae.
While in the past spheroidicity was assumed, and still is used in modeling of most nebulae, we kn... more While in the past spheroidicity was assumed, and still is used in modeling of most nebulae, we know now that only a small number of planetary nebulae (PNe) are really spherical or at least nearly round. Round planetary nebulae are the minority of objects. In case of those objects that underwent a very late helium flash (called VLTP or "born-again" PNe) it seems to be different. The first, hydrogen rich PN, is more or less round. The ejecta from the VLTP event is extremely asymmetrically. Angular momentum is mostly assumed to be the main reason for the asymmetry in PNe. Thus we have to find processes either changing their behavior within a few hundred to a few thousands of years or change their properties dramatically due to the variation of the abundance. They most likely have a strong link or dependency with the abundance of the ejecta.
IRAS 16594-4656 is a C-rich B[e]-type post-AGB star with a strong stellar wind, and maybe a disk.... more IRAS 16594-4656 is a C-rich B[e]-type post-AGB star with a strong stellar wind, and maybe a disk. Shocked H2 reveals the interaction of the post-AGB wind with the AGB shell and the shaping of the hollow bipolar shell. The shocked [Fe ii] 1.645 µm emission line originates in the stellar wind, or possibly in a disk, close to the central star. The [O i] and [C i] emission lines in the optical spectrum indicate the presence of a very high density region.
By measuring the abundances in nebulae, and distinguishing the enrichment of processed elements (... more By measuring the abundances in nebulae, and distinguishing the enrichment of processed elements (primarily He, C, N, and O) from non-processed elements, (chiefly Ar, Ne, S) we are able to probe both the chemical enrichment around the planetary nebula and the population type of the progenitor star. Where we can also determine the evolutionary state, and therefore the mass, of
Aims. In our series of papers presenting the Herschel imaging of evolved planetary nebulae, we pr... more Aims. In our series of papers presenting the Herschel imaging of evolved planetary nebulae, we present images of the dust distribution in the Helix nebula (NGC 7293). Methods. Images at 70, 160, 250, 350, and 500 µm were obtained with the PACS and SPIRE instruments on board the Herschel satellite. Results. The broadband maps show the dust distribution over the main Helix nebula to be clumpy and predominantly present in the barrel wall. We determined the spectral energy distribution of the main nebula in a consistent way using Herschel, IRAS, and Planck flux values. The emissivity index of β = 0.99 ± 0.09, in combination with the carbon rich molecular chemistry of the nebula, indicates that the dust consists mainly of amorphous carbon. The dust excess emission from the central star disk is detected at 70 µm and the flux measurement agrees with previous measurement. We present the temperature and dust column density maps. The total dust mass across the Helix nebula (without its halo) is determined to be 3.5 10 −3 M at a distance of 216 pc. The temperature map shows dust temperatures between 22 K and 42 K, which is similar to the kinetic temperature of the molecular gas, confirming that the dust and gas co-exist in high density clumps. Archived images are used to compare the location of the dust emission in the far infrared (Herschel) with the ionized (GALEX and Hβ) and molecular (H 2) component. The different emission components are consistent with the Helix consisting of a thick walled barrel-like structure inclined to the line of sight. The radiation field decreases rapidly through the barrel wall.
Context. The Helix Nebula (NGC 7293) is the closest planetary nebulae. Therefore, it is an ideal ... more Context. The Helix Nebula (NGC 7293) is the closest planetary nebulae. Therefore, it is an ideal template for photochemical studies at small spatial scales in planetary nebulae. Aims. We aim to study the spatial distribution of the atomic and the molecular gas, and the structure of the photodissociation region along the western rims of the Helix Nebula as seen in the submillimeter range with Herschel. Methods. We use 5 SPIRE FTS pointing observations to make atomic and molecular spectral maps. We analyze the molecular gas by modeling the CO rotational lines using a non-local thermodynamic equilibrium (non-LTE) radiative transfer model. Results. For the first time, we have detected extended OH + emission in a planetary nebula. The spectra towards the Helix Nebula also show CO emission lines (from J = 4 to 8), [N ii] at 1461 GHz from ionized gas, and [C i] (3 P 2 − 3 P 1), which together with the OH + lines, trace extended CO photodissociation regions along the rims. The estimated OH + column density is ∼ 10 12 − 10 13 cm −2. The CH + (1-0) line was not detected at the sensitivity of our observations. Non-LTE models of the CO excitation were used to constrain the average gas density (n(H 2) ∼ (1 − 5) × 10 5 cm −3) and the gas temperature (T k ∼ 20 − 40 K). Conclusions. The SPIRE spectral-maps suggest that CO arises from dense and shielded clumps in the western rims of the Helix Nebula whereas OH + and [C i] lines trace the diffuse gas and the UV and X-ray illuminated clumps surface where molecules reform after CO photodissociation. [N ii] traces a more diffuse ionized gas componnent in the interclump medium.
Gamma Doradus stars (hereafter γ Dor stars) are gravity-mode pulsators of spectral type A or F. S... more Gamma Doradus stars (hereafter γ Dor stars) are gravity-mode pulsators of spectral type A or F. Such modes probe the deep stellar interior, offering a detailed fingerprint of their structure. Four-year high-precision space-based Kepler photometry of γ Dor stars has become available, allowing us to study these stars with unprecedented detail. We selected, analysed, and characterized a sample of 67 γ Dor stars for which we have Kepler observations available. For all the targets in the sample we assembled high-resolution spectroscopy to confirm their F-type nature. We found fourteen binaries, among which four single-lined binaries, five double-lined binaries, two triple systems and three binaries with no detected radial velocity variations. We estimated the orbital parameters whenever possible. For the single stars and the single-lined binaries, fundamental parameter values were determined from spectroscopy. We searched for period spacing patterns in the photometric data and identified this diagnostic for 50 of the stars in the sample, 46 of which are single stars or single-lined binaries. We found a strong correlation between the spectroscopic v sin i and the period spacing values, confirming the influence of rotation on γ Dor-type pulsations as predicted by theory. We also found relations between the dominant g-mode frequency, the longest pulsation period detected in series of prograde modes, v sin i, and log T eff .
Proceedings of the International Astronomical Union, 2006
We report on the progress of our ongoing campaign to monitor the evolution of the VLTP objects V4... more We report on the progress of our ongoing campaign to monitor the evolution of the VLTP objects V4334 Sgr and V605 Aql, as well as the suspected (V)LTP object CK Vul. V4334 Sgr does not show signs of increased ionization compared to our previous observations in 2004. We obtained the first radio detection of V605 Aql, indicating a strong increase in radio flux since 1987. We also present the first radio detection of CK Vul and discuss the expansion of the material ejected during the 1670 event.
We report on our radial velocity monitoring project of a wide range of evolved stars where binari... more We report on our radial velocity monitoring project of a wide range of evolved stars where binarity was proposed to explain some of their peculiarities. Our spectrograph HERMES is a new optical echelle spectrograph mounted on the 1.2m Mercator telescope on La Palma, built by a consortium of Belgian Institutes (KULeuven, ULB, Royal Observatory) with contributions from the Geneva Observatory and Landessternwarte Tautenburg. By combining high S/N single observations with low S/N time-series, we aim at quantifying the orbital and chemical characteristics of every distinct subgroup. The final goal is to gain insight in the diverse binary interaction processes relevant at late stages of stellar evolution. We discuss our project, the unique capabilities of HERMES, and present the first results of our program.
Proceedings of the International Astronomical Union
To investigate the binary hypothesis in the formation of planetary nebulae, we have been doing lo... more To investigate the binary hypothesis in the formation of planetary nebulae, we have been doing long-term photometry and radial velocity (RV) monitoring of bright post-AGB stars which possess bipolar or ellipsoidal nebulae but no indication of a disk in their spectral energy distribution, indicative of a binary companion. RV’s are determined by cross correlating high-resolution spectra with a line mask. Stellar variability and companions both deform the cross correlation function (CCF) and induce periodic variations in the RV. To uniformly quantify the asymmetry of the CCF from a Gaussian, we propose to fit the CCF profile with a Gauss-Hermite series and determine all CCF parameters (RV, skewness, FWHM, and depth) in one single fit. We analyze the correlation and time series of these CCF parameters for V448 Lac and conclude that its RV variability is most likely due to stellar pulsation and not to an orbiting body.
Context. Hundreds of candidate hybrid pulsators of intermediate type A–F were revealed by recent ... more Context. Hundreds of candidate hybrid pulsators of intermediate type A–F were revealed by recent space missions. Hybrid pulsators allow us to study the full stellar interiors, where both low-order p- and high-order g-modes are simultaneously excited. The true hybrid stars must be identified since other processes, related to stellar multiplicity or rotation, might explain the presence of (some) low frequencies observed in their periodograms. Aims. We measured the radial velocities of 50 candidate δ Scuti −γ Doradus hybrid stars from the Kepler mission with the Hermes and ace spectrographs over a time span of months to years. We aim to derive the fraction of binary and multiple systems and to provide an independent and homogeneous determination of the atmospheric properties and v sin i for all targets. The long(er)-term objective is to identify the (probable) physical cause of the low frequencies. Methods. We computed one-dimensional cross-correlation functions (CCFs) in order to find...
Proceedings of the International Astronomical Union
V4334 Sgr (a.k.a. Sakurai's object) is the central star of an old planetary nebula that under... more V4334 Sgr (a.k.a. Sakurai's object) is the central star of an old planetary nebula that underwent a very late thermal pulse a few years before its discovery in 1996. We have been monitoring the evolution of the optical emission line spectrum since 2001. The goal is to improve the evolutionary models by constraining them with the temporal evolution of the central star temperature. In addition the high resolution spectral observations obtained by X-shooter and ALMA show the temporal evolution of the different morphological components.
While in the past spherodicity was assumed, and still is used in modeling of most nebulae, we kno... more While in the past spherodicity was assumed, and still is used in modeling of most nebulae, we know now that only a small number of planetary nebulae (PNe) are really spherical or at least nearly round. Round planetary nebulae are the minority of objects. In the case of those objects that underwent a very late helium flash (called VLTP objects
While in the past spheroidicity was assumed, and still is used in modeling of most nebulae, we kn... more While in the past spheroidicity was assumed, and still is used in modeling of most nebulae, we know now that only a small number of planetary nebulae (PNe) are really spherical or at least nearly round. Round planetary nebulae are the minority of objects. In case of those objects that underwent a very late helium flash (called VLTP or "born-again" PNe) it seems to be different. The first, hydrogen rich PN, is more or less round. The ejecta from the VLTP event is extremely asymmetrically. Angular momentum is mostly assumed to be the main reason for the asymmetry in PNe. Thus we have to find processes either changing their behavior within a few hundred to a few thousands of years or change their properties dramatically due to the variation of the abundance. They most likely have a strong link or dependency with the abundance of the ejecta.
While in the past spheroidicity was assumed, and still is used in modeling of most nebulae, we kn... more While in the past spheroidicity was assumed, and still is used in modeling of most nebulae, we know now that only a small number of planetary nebulae (PNe) are really spherical or at least nearly round. Round planetary nebulae are the minority of objects. In case of those objects that underwent a very late helium flash (called VLTP or "born-again" PNe) it seems to be different. The first, hydrogen rich PN, is more or less round. The ejecta from the VLTP event is extremely asymmetrically. Angular momentum is mostly assumed to be the main reason for the asymmetry in PNe. Thus we have to find processes either changing their behavior within a few hundred to a few thousands of years or change their properties dramatically due to the variation of the abundance. They most likely have a strong link or dependency with the abundance of the ejecta.
The results from a Hubble Space T elescope (HST) snapshot survey of post-AGB objects are shown. T... more The results from a Hubble Space T elescope (HST) snapshot survey of post-AGB objects are shown. The aim of the survey is to complement existing HST images of PPN and to connect various types of nebulosities with physical and chemical properties of their central stars. Nebulosities are detected in 15 of 33 sources. Images and photometric and geometric measurements are presented. For sources with nebulosities we see a morphological bifurcation into two groups, DUPLEX and SOLE, as previous studies have found. We find further support to the previous results suggesting that this dichotomy is caused by a difference in optical thickness of the dust shell. The remaining 18 sources are classified as stellar post-AGB objects, because our observations indicate a lack of nebulosity. We show that some stellar sources may in fact be DUPLEX or SOLE based on their infrared colors. The cause of the differences among the groups are investigated. We discuss some evidence suggesting that high progenitor-mass AGB stars tend to become DUPLEX post-AGB objects. Intermediate progenitormass AGB stars tend to be SOLE post-AGB objects. Most of the stellar sources probably have low mass progenitors and do not seem to develop nebulosities during the post-AGB phase and therefore do not become planetary nebulae.
While in the past spheroidicity was assumed, and still is used in modeling of most nebulae, we kn... more While in the past spheroidicity was assumed, and still is used in modeling of most nebulae, we know now that only a small number of planetary nebulae (PNe) are really spherical or at least nearly round. Round planetary nebulae are the minority of objects. In case of those objects that underwent a very late helium flash (called VLTP or "born-again" PNe) it seems to be different. The first, hydrogen rich PN, is more or less round. The ejecta from the VLTP event is extremely asymmetrically. Angular momentum is mostly assumed to be the main reason for the asymmetry in PNe. Thus we have to find processes either changing their behavior within a few hundred to a few thousands of years or change their properties dramatically due to the variation of the abundance. They most likely have a strong link or dependency with the abundance of the ejecta.
IRAS 16594-4656 is a C-rich B[e]-type post-AGB star with a strong stellar wind, and maybe a disk.... more IRAS 16594-4656 is a C-rich B[e]-type post-AGB star with a strong stellar wind, and maybe a disk. Shocked H2 reveals the interaction of the post-AGB wind with the AGB shell and the shaping of the hollow bipolar shell. The shocked [Fe ii] 1.645 µm emission line originates in the stellar wind, or possibly in a disk, close to the central star. The [O i] and [C i] emission lines in the optical spectrum indicate the presence of a very high density region.
By measuring the abundances in nebulae, and distinguishing the enrichment of processed elements (... more By measuring the abundances in nebulae, and distinguishing the enrichment of processed elements (primarily He, C, N, and O) from non-processed elements, (chiefly Ar, Ne, S) we are able to probe both the chemical enrichment around the planetary nebula and the population type of the progenitor star. Where we can also determine the evolutionary state, and therefore the mass, of
Aims. In our series of papers presenting the Herschel imaging of evolved planetary nebulae, we pr... more Aims. In our series of papers presenting the Herschel imaging of evolved planetary nebulae, we present images of the dust distribution in the Helix nebula (NGC 7293). Methods. Images at 70, 160, 250, 350, and 500 µm were obtained with the PACS and SPIRE instruments on board the Herschel satellite. Results. The broadband maps show the dust distribution over the main Helix nebula to be clumpy and predominantly present in the barrel wall. We determined the spectral energy distribution of the main nebula in a consistent way using Herschel, IRAS, and Planck flux values. The emissivity index of β = 0.99 ± 0.09, in combination with the carbon rich molecular chemistry of the nebula, indicates that the dust consists mainly of amorphous carbon. The dust excess emission from the central star disk is detected at 70 µm and the flux measurement agrees with previous measurement. We present the temperature and dust column density maps. The total dust mass across the Helix nebula (without its halo) is determined to be 3.5 10 −3 M at a distance of 216 pc. The temperature map shows dust temperatures between 22 K and 42 K, which is similar to the kinetic temperature of the molecular gas, confirming that the dust and gas co-exist in high density clumps. Archived images are used to compare the location of the dust emission in the far infrared (Herschel) with the ionized (GALEX and Hβ) and molecular (H 2) component. The different emission components are consistent with the Helix consisting of a thick walled barrel-like structure inclined to the line of sight. The radiation field decreases rapidly through the barrel wall.
Context. The Helix Nebula (NGC 7293) is the closest planetary nebulae. Therefore, it is an ideal ... more Context. The Helix Nebula (NGC 7293) is the closest planetary nebulae. Therefore, it is an ideal template for photochemical studies at small spatial scales in planetary nebulae. Aims. We aim to study the spatial distribution of the atomic and the molecular gas, and the structure of the photodissociation region along the western rims of the Helix Nebula as seen in the submillimeter range with Herschel. Methods. We use 5 SPIRE FTS pointing observations to make atomic and molecular spectral maps. We analyze the molecular gas by modeling the CO rotational lines using a non-local thermodynamic equilibrium (non-LTE) radiative transfer model. Results. For the first time, we have detected extended OH + emission in a planetary nebula. The spectra towards the Helix Nebula also show CO emission lines (from J = 4 to 8), [N ii] at 1461 GHz from ionized gas, and [C i] (3 P 2 − 3 P 1), which together with the OH + lines, trace extended CO photodissociation regions along the rims. The estimated OH + column density is ∼ 10 12 − 10 13 cm −2. The CH + (1-0) line was not detected at the sensitivity of our observations. Non-LTE models of the CO excitation were used to constrain the average gas density (n(H 2) ∼ (1 − 5) × 10 5 cm −3) and the gas temperature (T k ∼ 20 − 40 K). Conclusions. The SPIRE spectral-maps suggest that CO arises from dense and shielded clumps in the western rims of the Helix Nebula whereas OH + and [C i] lines trace the diffuse gas and the UV and X-ray illuminated clumps surface where molecules reform after CO photodissociation. [N ii] traces a more diffuse ionized gas componnent in the interclump medium.
Gamma Doradus stars (hereafter γ Dor stars) are gravity-mode pulsators of spectral type A or F. S... more Gamma Doradus stars (hereafter γ Dor stars) are gravity-mode pulsators of spectral type A or F. Such modes probe the deep stellar interior, offering a detailed fingerprint of their structure. Four-year high-precision space-based Kepler photometry of γ Dor stars has become available, allowing us to study these stars with unprecedented detail. We selected, analysed, and characterized a sample of 67 γ Dor stars for which we have Kepler observations available. For all the targets in the sample we assembled high-resolution spectroscopy to confirm their F-type nature. We found fourteen binaries, among which four single-lined binaries, five double-lined binaries, two triple systems and three binaries with no detected radial velocity variations. We estimated the orbital parameters whenever possible. For the single stars and the single-lined binaries, fundamental parameter values were determined from spectroscopy. We searched for period spacing patterns in the photometric data and identified this diagnostic for 50 of the stars in the sample, 46 of which are single stars or single-lined binaries. We found a strong correlation between the spectroscopic v sin i and the period spacing values, confirming the influence of rotation on γ Dor-type pulsations as predicted by theory. We also found relations between the dominant g-mode frequency, the longest pulsation period detected in series of prograde modes, v sin i, and log T eff .
Proceedings of the International Astronomical Union, 2006
We report on the progress of our ongoing campaign to monitor the evolution of the VLTP objects V4... more We report on the progress of our ongoing campaign to monitor the evolution of the VLTP objects V4334 Sgr and V605 Aql, as well as the suspected (V)LTP object CK Vul. V4334 Sgr does not show signs of increased ionization compared to our previous observations in 2004. We obtained the first radio detection of V605 Aql, indicating a strong increase in radio flux since 1987. We also present the first radio detection of CK Vul and discuss the expansion of the material ejected during the 1670 event.
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Papers by G. Steene