- ID:
- ivo://CDS.VizieR/J/ApJ/836/186
- Title:
- Continuum-band lags in SDSS QSOs from PS1 obs.
- Short Name:
- J/ApJ/836/186
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the time lags between the continuum emission of quasars at different wavelengths, based on more than four years of multi-band (g, r, i, z) light curves in the Pan-STARRS Medium Deep Fields. As photons from different bands emerge from different radial ranges in the accretion disk, the lags constrain the sizes of the accretion disks. We select 240 quasars with redshifts of z~1 or z~0.3 that are relatively emission-line free. The light curves are sampled from day to month timescales, which makes it possible to detect lags on the scale of the light crossing time of the accretion disks. With the code JAVELIN, we detect typical lags of several days in the rest frame between the g band and the riz bands. The detected lags are ~2-3 times larger than the light crossing time estimated from the standard thin disk model, consistent with the recently measured lag in NGC 5548 and microlensing measurements of quasars. The lags in our sample are found to increase with increasing luminosity. Furthermore, the increase in lags going from g-r to g-i and then to g-z is slower than predicted in the thin disk model, particularly for high-luminosity quasars. The radial temperature profile in the disk must be different from what is assumed. We also find evidence that the lags decrease with increasing line ratios between ultraviolet Fe II lines and Mg II, which may point to changes in the accretion disk structure at higher metallicity.
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- ID:
- ivo://CDS.VizieR/J/ApJ/866/133
- Title:
- Continuum-H{beta} light curves of 5 Seyfert 1
- Short Name:
- J/ApJ/866/133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first results from a reverberation-mapping campaign undertaken during the first half of 2012, with additional data on one active galactic nucleus (AGN) (NGC 3227) from a 2014 campaign. Our main goals are (1) to determine the black hole masses from continuum-H{beta} reverberation signatures, and (2) to look for velocity-dependent time delays that might be indicators of the gross kinematics of the broad-line region. We successfully measure H{beta} time delays and black hole masses for five AGNs, four of which have previous reverberation mass measurements. The values measured here are in agreement with earlier estimates, though there is some intrinsic scatter beyond the formal measurement errors. We observe velocity-dependent H{beta} lags in each case, and find that the patterns have changed in the intervening five years for three AGNs that were also observed in 2007.
- ID:
- ivo://CDS.VizieR/J/A+A/588/A97
- Title:
- Continuum sources from the THOR survey
- Short Name:
- J/A+A/588/A97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We carried out a large program with the Karl G. Jansky Very Large Array (VLA): "THOR: The HI, OH, Recombination line survey of the Milky Way". We observed a significant portion of the Galactic plane in the first quadrant of the Milky Way in the 21cm HI line, 4 OH transitions, 19 radio recombination lines, and continuum from 1 to 2GHz. In this paper we present a catalog of the continuum sources in the first half of the survey (l=14.0-37.9{deg} and l=47.1-51.2{deg}, |b|<1.1{deg}) at a spatial resolution of 10-25", depending on the frequency and sky position with a spatially varying noise level of ~0.3-1mJy/beam. The catalog contains ~4400 sources. Around 1200 of these are spatially resolved, and ~1000 are possible artifacts, given their low signal-to-noise ratios. Since the spatial distribution of the unresolved objects is evenly distributed and not confined to the Galactic plane, most of them are extragalactic. Thanks to the broad bandwidth of the observations from 1 to 2GHz, we are able to determine a reliable spectral index for ~1800 sources. The spectral index distribution reveals a double-peaked profile with maxima at spectral indices of alpha=-1 and alpha=0, corresponding to steep declining and flat spectra, respectively. This allows us to distinguish between thermal and non-thermal emission, which can be used to determine the nature of each source. We examine the spectral index of ~300 known HII regions, for which we find thermal emission with spectral indices around alpha=0. In contrast, supernova remnants (SNR) show non-thermal emission with alpha=-0.5 and extragalactic objects generally have a steeper spectral index of alpha=-1. Using the spectral index information of the THOR survey, we investigate potential SNR candidates. We classify the radiation of four SNR candidates as non-thermal, and for the first time, we provide strong evidence for the SNR origin of these candidates.
- ID:
- ivo://CDS.VizieR/J/A+A/654/A168
- Title:
- Convective blueshifts for solar-type stars
- Short Name:
- J/A+A/654/A168
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The detection of earth-mass exoplanets in the habitable zone around solar-mass stars using the radial velocity technique requires extremely high- precision of the order of 10cm/s. This puts the required noise floor below the intrinsic variability of even relatively inactive stars, like the Sun. One such variable is convective blueshift varying temporally, spatially and between spectral lines. We develop a novel approach to measure convective blueshift and determine the strength of convective blueshift for 810 stars observed by the HARPS spectrograph, spanning spectral types from late-F, G, K to early-M. We derive a model to infer blueshift velocity for lines of any depth in later-type stars of any effective temperature. Using a custom list of spectral lines, covering a wide range of absorption depths, we create a model for the line-core shift as a function of line depth, commonly known as the third signature of granulation. For this we utilize an extremely high-resolution solar spectrum (R~1.000.000) to empirically account for the non-linear nature of the third signature. The solar third signature is then scaled to all 810 stars. Through this we obtain a measure of the convective blueshift relative to the Sun as a function of stellar effective temperature. We confirm the general correlation of increasing convective blueshift with effective temperature and establish a tight, cubic relation between the two that strongly increases for stars above ~5800K. For stars between ~4100K and ~4700K we show for the first time a plateau in convective shift and a possible onset of a plateau for stars above 6000K. Stars below ~4000K show neither blue or red shift. We provide a table listing expected blueshift velocities for each spectral subtype in the data set to quickly access the intrinsic noise floor through convective blueshift for the RV technique.
- ID:
- ivo://CDS.VizieR/J/A+A/624/A57
- Title:
- Convective blueshifts in solar atmos.
- Short Name:
- J/A+A/624/A57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Convective motions in the solar atmosphere cause spectral lines to become asymmetric and shifted in wavelength. For photospheric lines, this differential Doppler shift varies from the solar disk center to the limb. Precise and comprehensive observations of the convective blueshift and its center-to-limb variation improve our understanding of the atmospheric hydrodynamics and ensuing line formation, and provide the basis to refine 3D models of the solar atmosphere. We performed systematical spectroscopic measurements of the convective blueshift of the quiet Sun with the Laser Absolute Reference Spectrograph (LARS) at the German Vacuum Tower Telescope. The spatial scanning of the solar disk covered 11 heliocentric positions each along four radial (meridional and equatorial) axes. The high-resolution spectra of 26 photospheric to chromospheric lines in the visible range were calibrated with a laser frequency comb to absolute wavelengths at the 1m/s accuracy. Applying ephemeris and reference corrections, the bisector analysis provided line asymmetries and Doppler shifts with an uncertainty of only few m/s. To allow for a comparison with other observations, we convolved the results to lower spectral resolutions.
- ID:
- ivo://CDS.VizieR/J/ApJ/738/119
- Title:
- Conversion from magnetoacoustic to Alfven waves
- Short Name:
- J/ApJ/738/119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Alfven waves may be generated via mode conversion from fast magnetoacoustic waves near their reflection level in the solar atmosphere, with implications both for coronal oscillations and for active region helioseismology. In active regions this reflection typically occurs high enough that the Alfven speed a greatly exceeds the sound speed c, well above the a=c level where the fast and slow modes interact. In order to focus on the fundamental characteristics of fast/Alfven conversion, stripped of unnecessary detail, it is therefore useful to freeze out the slow mode by adopting the gravitationally stratified cold magnetohydrodynamic model c->0. This provides a benchmark for fast-to-Alfven mode conversion in more complex atmospheres. Assuming a uniform inclined magnetic field and an exponential Alfven speed profile with density scale height h, the Alfven conversion coefficient depends on three variables only: the dimensionless transverse-to-the-stratification wavenumber {kappa}=kh, the magnetic field inclination from the stratification direction {theta}, and the polarization angle {phi} of the wavevector relative to the plane containing the stratification and magnetic field directions. We present an extensive exploration of mode conversion in this parameter space and conclude that near-total conversion to outward-propagating Alfven waves typically occurs for small {theta} and large {phi} (80-90{deg}), though it is absent entirely when {theta} is exactly zero (vertical field). For wavenumbers of helioseismic interest, the conversion region is broad enough to encompass the whole chromosphere.
- ID:
- ivo://CDS.VizieR/J/A+A/411/381
- Title:
- CO observation of isolated galaxies
- Short Name:
- J/A+A/411/381
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present ^12^CO(J=1-0) line observations of 99 galaxies obtained with the SEST 15m, the Kitt Peak 12m and the IRAM 30m telescopes. The target galaxies were selected from the catalogue of isolated galaxies of Karachentseva (1973, Cat. <VII/82>). These data are thus representative of the CO properties of isolated late-type galaxies. All objects were observed in their central position, those with large angular sizes were mapped. These new measurements are used to estimate the molecular gas mass of the target galaxies. The molecular gas is on average ~18% of the atomic gas mass.
- ID:
- ivo://CDS.VizieR/J/ApJ/761/37
- Title:
- CO observations in giant molecular clouds of M33
- Short Name:
- J/ApJ/761/37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a giant molecular cloud (GMC) catalog of M33 (NGC598), containing 71 GMCs in total, based on wide-field and high-sensitivity CO(J=3-2) observations with a spatial resolution of 100pc using the ASTE 10m telescope. Employing archival optical data, we identify 75 young stellar groups (YSGs) from the excess of the surface stellar density, and estimate their ages by comparing with stellar evolution models. A spatial comparison among the GMCs, YSGs, and H II regions enable us to classify GMCs into four categories: Type A, showing no sign of massive star formation (SF); Type B, being associated only with H II regions; Type C, with both H II regions and <10Myr old YSGs; and Type D, with both H II regions and 10-30Myr YSGs. Out of 65 GMCs (discarding those at the edges of the observed fields), 1 (1%), 13 (20%), 29 (45%), and 22 (34%) are Types A, B, C, and D, respectively. We interpret these categories as stages in a GMC evolutionary sequence. Assuming that the timescale for each evolutionary stage is proportional to the number of GMCs, the lifetime of a GMC with a mass >10^5^M_{sun}_ is estimated to be 20-40Myr. In addition, we find that the dense gas fraction as traced by the CO(J=3-2)/CO(J=1-0) ratio is enhanced around SF regions. This confirms a scenario where dense gas is preferentially formed around previously generated stars, and will be the fuel for the next stellar generation. In this way, massive SF gradually propagates in a GMC until gas is exhausted.
- ID:
- ivo://CDS.VizieR/J/A+A/295/585
- Title:
- CO observations in NGC 1365
- Short Name:
- J/A+A/295/585
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of the J=1-0 and J=2-1 CO observations are presented
- ID:
- ivo://CDS.VizieR/J/A+AS/118/47
- Title:
- CO observations in spirals
- Short Name:
- J/A+AS/118/47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 1300{mu}m continuum observations and measurements of the CO (1-0) and (2-1) emission from the inner regions of 98 normal galaxies. The spatial resolution ranges from 11arcsec to 45arcsec. The sources come from a complete FIR selected sample of 138 inactive spirals with an optical diameter D_25_<=180arcsec.