- ID:
- ivo://CDS.VizieR/J/ApJ/852/72
- Title:
- Luminosity functions of tidal disruption flares
- Short Name:
- J/ApJ/852/72
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The tidal disruption of a star by a massive black hole is expected to yield a luminous flare of thermal emission. About two dozen of these stellar tidal disruption flares (TDFs) may have been detected in optical transient surveys. However, explaining the observed properties of these events within the tidal disruption paradigm is not yet possible. This theoretical ambiguity has led some authors to suggest that optical TDFs are due to a different process, such as a nuclear supernova or accretion disk instabilities. Here we present a test of a fundamental prediction of the tidal disruption event scenario: a suppression of the flare rate due to the direct capture of stars by the black hole. Using a recently compiled sample of candidate TDFs with black hole mass measurements, plus a careful treatment of selection effects in this flux-limited sample, we confirm that the dearth of observed TDFs from high-mass black holes is statistically significant. All the TDF impostor models we consider fail to explain the observed mass function; the only scenario that fits the data is a suppression of the rate due to direct captures. We find that this suppression can explain the low volumetric rate of the luminous TDF candidate ASASSN-15lh, thus supporting the hypothesis that this flare belongs to the TDF family. Our work is the first to present the optical TDF luminosity function. A steep power law is required to explain the observed rest-frame g-band luminosity, dN/dL_g_{propto}L_g_^-2.5^. The mean event rate of the flares in our sample is ~1x10^-4^galaxy^-1^/yr, consistent with the theoretically expected tidal disruption rate.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/157/22
- Title:
- Luminous and variable stars in NGC 2403 and M81
- Short Name:
- J/AJ/157/22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of spectroscopy and multi-wavelength photometry of luminous and variable star candidates in the nearby spiral galaxies NGC 2403 and M81. We discuss specific classes of stars, the Luminous Blue Variables (LBVs), B[e] supergiants (sgB[e]), and the high-luminosity yellow hypergiants. We identify two new LBV candidates, and three sgB[e] stars in M81. We also find that some stars that were previously considered LBV candidates are actually field stars. The confirmed and candidate LBVs and sgB[e] stars together with the other confirmed members are shown on the HR Diagrams for their respective galaxies. We also present the HR Diagrams for the two "SN impostors", V37 (SN2002kg) and V12 (SN1954J) in NGC 2403 and the stars in their immediate environments.
- ID:
- ivo://CDS.VizieR/J/MNRAS/478/3138
- Title:
- Luminous cool supergiants in Magellanic Clouds
- Short Name:
- J/MNRAS/478/3138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The empirical upper luminosity boundary L_max_ of cool supergiants, often referred to as the Humphreys-Davidson limit, is thought to encode information on the general mass-loss behaviour of massive stars. Further, it delineates the boundary at which single stars will end their lives stripped of their hydrogen-rich envelope, which in turn is a key factor in the relative rates of Type-II to Type-Ibc supernovae from single star channels. In this paper we have revisited the issue of L_max_ by studying the luminosity distributions of cool supergiants (SGs) in the Large and Small Magellanic Clouds (LMC/SMC). We assemble highly-complete samples of cool SGs in each galaxy, and determine their spectral energy distributions from the optical to the mid-infrared using modern multi-wavelength survey data. We show that in both cases L_max_ appears to be lower than previously quoted, and is in the region of logL/L_{sun}_=5.5. There is no evidence for L_max_ being higher in the SMC than in the LMC, as would be expected if metallicity-dependent winds were the dominant factor in the stripping of stellar envelopes. We also show that L_max_ aligns with the lowest luminosity of single nitrogen-rich Wolf-Rayet stars, indicating of a change in evolutionary sequence for stars above a critical mass. From population synthesis analysis we show that the Geneva evolutionary models greatly over-predict the numbers of cool SGs in the SMC. We also argue that the trend of earlier average spectral types of cool SGs in lower metallicity environments represents a genuine shift to hotter temperatures. Finally, we use our new bolometric luminosity measurements to provide updated bolometric corrections for cool supergiants.
- ID:
- ivo://CDS.VizieR/J/ApJ/836/64
- Title:
- Luminous variable stars in M31 & M33. IV.
- Short Name:
- J/ApJ/836/64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this series of papers we have presented the results of a spectroscopic survey of luminous stars in the nearby spirals M31 and M33. Here, we present spectroscopy of 132 additional stars. Most have emission-line spectra, including luminous blue variables (LBVs) and candidate LBVs, Fe II emission line stars, the B[e] supergiants, and the warm hypergiants. Many of these objects are spectroscopically similar and are often confused with each other. We examine their similarities and differences and propose the following guidelines that can be used to help distinguish these stars in future work. (1) The B[e] supergiants have emission lines of [OI] and [FeII] in their spectra. Most of the spectroscopically confirmed sgB[e] stars also have warm circumstellar dust in their spectral energy distributions (SEDs). (2) Confirmed LBVs do not have the [OI] emission lines in their spectra. Some LBVs have [FeII] emission lines, but not all. Their SEDs show free-free emission in the near-infrared but no evidence for warm dust. Their most important and defining characteristic is the S Dor-type variability. (3) The warm hypergiants spectroscopically resemble the LBVs in their dense wind state and the B[e] supergiants. However, they are very dusty. Some have [FeII] and [OI] emission in their spectra like the sgB[e] stars, but are distinguished by their A- and F-type absorption-line spectra. In contrast, the B[e] supergiant spectra have strong continua and few if any apparent absorption lines. Candidate LBVs should share the spectral characteristics of the confirmed LBVs with low outflow velocities and the lack of warm circumstellar dust.
- ID:
- ivo://CDS.VizieR/J/A+A/521/A19
- Title:
- 21 Lutetia UBVRI light curves
- Short Name:
- J/A+A/521/A19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Asteroid 21 Lutetia is the second target of the Rosetta space mission. Extensive pre-encounter, space-, and ground-based observations are being performed to prepare for the flyby in July 2010. The aim of this article is to accurately characterize the photometric properties of this asteroid over a broad spectral range from the ultraviolet to the near-infrared and to search for evidence of surface inhomogeneities.
- ID:
- ivo://CDS.VizieR/J/MNRAS/445/881
- Title:
- LVL global optical photometry
- Short Name:
- J/MNRAS/445/881
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the global optical photometry of 246 galaxies in the Local Volume Legacy (LVL) survey. The full volume-limited sample consists of 258 nearby (D<11Mpc) galaxies whose absolute B-band magnitude span a range of -9.6<M_B_<-20.7mag. A composite optical (UBVR) data set is constructed from observed UBVR and Sloan Digital Sky Survey ugriz imaging, where the ugriz magnitudes are transformed into UBVR. We present photometry within three galaxy apertures defined at UV, optical, and IR wavelengths. Flux comparisons between these apertures reveal that the traditional optical R25 galaxy apertures do not fully encompass extended sources. Using the larger IR apertures, we find colour-colour relationships where later type spiral and irregular galaxies tend to be bluer than earlier type galaxies. These data provide the missing optical emission from which future LVL studies can construct the full panchromatic (UV-optical-IR) spectral energy distributions.
- ID:
- ivo://CDS.VizieR/J/ApJ/696/546
- Title:
- Ly{alpha} emitters at z~4.86
- Short Name:
- J/ApJ/696/546
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of a survey for Ly{alpha} emitters at z~4.86 based on optical narrowband ({lambda}c=7126{AA}, {Delta}{lambda}=73{AA}) and broadband (B, V, r', i', and z') observations of the Cosmic Evolution Survey field using Suprime-Cam on the Subaru Telescope. We find 79 Ly{alpha} emitter (LAE) candidates at z~4.86 over a contiguous survey area of 1.83deg^2^, down to the Ly{alpha} line flux of 1.47x10^-17^erg/s/cm^2^. We obtain the Ly{alpha} luminosity function with a best-fit Schechter parameters of log L*=42.9^+0.5^_-0.3_erg/s and {Phi}*=1.2^+8.0^_-1.1_x10^-4^Mpc^-3^ for {alpha}=-1.5 (fixed). The two-point correlation function for our LAE sample is {xi}(r)=(r/4.4^+5.7^_-2.9_Mpc)^-1.90+/-0.22^. In order to investigate the field-to-field variations of the properties of Ly{alpha} emitters, we divide the survey area into nine tiles of 0.5x0.5{deg} each. We find that the number density varies with a factor of ~2 from field to field with high statistical significance. However, we find no significant field-to-field variance when we divide the field into four tiles with 0.7x0.7{deg} each. We conclude that at least 0.5deg^2^ survey area is required to derive averaged properties of LAEs at z~5, and our survey field is wide enough to overcome the cosmic variance.
- ID:
- ivo://CDS.VizieR/J/other/NewA/51.59
- Title:
- LY And photometric followup
- Short Name:
- J/other/NewA/51.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a low-dispersion spectrum and two sets of CCD photometric light curves of the eclipsing binary LY And for the first time. The spectrum of LY And was classified as G2. We derived an updated ephemeris based on all previously available and our newly acquired minimum light times. Our analyses of LY And light curve minimum times reveals that the differences between calculated and observed minimum times for LY And can be represented by an upward parabolic curve, which means its orbital period is increasing with a rate of 1.88 (+/-0.13)x10^-7^days/year. This increase in orbital period may be interpreted as mass transfer from the primary component to the secondary component, with a rate of dM1/dt=-4.54x10^-8^M_{sun}_/year. By analyzing our CCD photometric light curves obtained in 2015, we obtained its photometric solution with the Wilson-Devinney program. This photometric solution also fits very well our light curves obtained in 2014. Our photometric solution shows that LY And is a contact eclipsing binary and its contact factor is f=(17.8+/-1.9)%. Furthermore, both our spectroscopic and photometric data show no obvious chromospheric activity of LY And.
- ID:
- ivo://CDS.VizieR/J/ApJ/736/48
- Title:
- 48 Lyman break galaxies at z~3 in HUDF
- Short Name:
- J/ApJ/736/48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present evidence for spatially extended low surface brightness emission around Lyman break galaxies (LBGs) in the V-band image of the Hubble Ultra Deep Field, corresponding to the z~3 rest-frame far-UV (FUV) light, which is a sensitive measure of star formation rates (SFRs). We find that the covering fraction of molecular gas at z~3 is not adequate to explain the emission in the outskirts of LBGs, while the covering fraction of neutral atomic-dominated hydrogen gas at high redshift is sufficient. We develop a theoretical framework to connect this emission around LBGs to the expected emission from neutral HI gas, i.e., damped Ly{alpha} systems (DLAs), using the Kennicutt-Schmidt (KS) relation. Working under the hypothesis that the observed FUV emission in the outskirts of LBGs is from in situ star formation in atomic-dominated hydrogen gas, the results suggest that the SFR efficiency in such gas at z~3 is between factors of 10 and 50 lower than predictions based on the local KS relation. The total SFR density in atomic-dominated gas at z~3 is constrained to be ~10% of that observed from the inner regions of LBGs. In addition, the metals produced by in situ star formation in the outskirts of LBGs yield metallicities comparable to those of DLAs, which is a possible solution to the "Missing Metals" problem for DLAs. Finally, the atomic-dominated gas in the outskirts of galaxies at both high and low redshifts has similar reduced SFR efficiencies and is consistent with the same power law.
- ID:
- ivo://CDS.VizieR/J/MNRAS/465/316
- Title:
- Lyman continuum LAEs and LBGs in SSA22 field
- Short Name:
- J/MNRAS/465/316
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the largest to date sample of hydrogen Lyman continuum (LyC) emitting galaxy candidates at any redshift, with 18 Lyman {alpha} emitters (LAEs) and seven Lyman break galaxies (LBGs), obtained from the SSA22 field with Subaru/Suprime-Cam. The sample is based on the 159 LAEs and 136 LBGs observed in the field, all with spectroscopically confirmed redshifts, and these LyC candidates are selected as galaxies with counterparts in a narrow-band filter image which traces LyC at z>=3.06. Many LyC candidates show a spatial offset between the rest-frame non-ionizing ultraviolet (UV) detection and the LyC-emitting substructure or between the Ly{alpha} emission and LyC. The possibility of foreground contamination complicates the analysis of the nature of LyC emitters, although statistically it is highly unlikely that all candidates in our sample are contaminated by foreground sources. Many viable LyC LAE candidates have flux density ratios inconsistent with standard models, while also having too blue UV slopes to be foreground contaminants. Stacking reveals no significant LyC detection, suggesting that there is a dearth of objects with marginal LyC signal strength, perhaps due to a bimodality in the LyC emission. The foreground contamination corrected 3{sigma} upper limits of the observed average flux density ratios are fLyC/fUV < 0.08 from stacking LAEs and f_LyC_/f_UV_<0.02 from stacking LBGs. There is a sign of a positive correlation between LyC and Ly{alpha}, suggesting that both types of photons escape via a similar mechanism. The LyC detection rate among protocluster LBGs is seemingly lower compared to the field.
