Search

Start Over Subject h alpha photometry Capability Type Simple Cone Search
101. Star formation in Centaurus A Group dwarfs
ID:
ivo://CDS.VizieR/J/AJ/138/1037
Title:
Star formation in Centaurus A Group dwarfs
Short Name:
J/AJ/138/1037
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present H{alpha} narrow-band imaging of 17 dwarf irregular (dI) galaxies in the nearby Centaurus A Group. Although all large galaxies of the group are or recently have been through a period of enhanced star formation, the dIs have normal star formation rates (SFRs) and do not contain a larger fraction of dwarf starbursts than other nearby groups such as the Sculptor Group or the Local Group. Most of the galaxies in the group now have fairly accurately known distances, which enables us to obtain relative distances between dIs and larger galaxies of the group. We find four transition dwarfs in the Group, dwarfs that show characteristics of both dE/dSphs and dIs, and which contain cold gas but no current star formation.
102. Star formation in nuclear rings
ID:
ivo://CDS.VizieR/J/ApJS/174/337
Title:
Star formation in nuclear rings
Short Name:
J/ApJS/174/337
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results from a photometric H{alpha} survey of 22 nuclear rings, aiming to provide insight into their star formation properties, including age distribution, dynamical timescales, star formation rates, and galactic bar influence. We find a clear relationship between the position angles and ellipticities of the rings and those of their host galaxies, which indicates the rings are in the same plane as the disk and circular. We use population synthesis models to estimate ages of each H{alpha}-emitting (HII) region, which range from 1 to 10Myr throughout the rings. We find that approximately half of the rings contain azimuthal age gradients that encompass at least 25% of the ring, although there is no apparent relationship between the presence or absence of age gradients and the morphology of the rings or their host galaxies. NGC 1343, NGC 1530, and NGC 4321 show clear bipolar age gradients, where the youngest HII regions are located near the two contact points of the bar and ring. We speculate in these cases that the gradients are related to an increased mass inflow rate and/or an overall higher gas density in the ring, which would allow for massive star formation to occur on short timescales, after which the galactic rotation would transport the HII regions around the ring as they age. Two-thirds of the barred galaxies show correlation between the locations of the youngest HII region(s) in the ring and the location of the contact points, which is consistent with predictions from numerical modeling.
103. Star formation rate distribution in NGC 1232
ID:
ivo://CDS.VizieR/J/AJ/155/234
Title:
Star formation rate distribution in NGC 1232
Short Name:
J/AJ/155/234
Date:
22 Feb 2022
Publisher:
CDS
Description:
NGC 1232 is a face-on spiral galaxy and a great laboratory for the study of star formation due to its proximity. We obtained high spatial resolution H{alpha} images of this galaxy, with adaptive optics, using the SAM instrument at the SOAR telescope, and used these images to study its H II regions. These observations allowed us to produce the most complete H II region catalog for it to date, with a total of 976 sources. This doubles the number of H II regions previously found for this object. We used these data to construct the H II luminosity function, and obtained a power-law index lower than the typical values found for Sc galaxies. This shallower slope is related to the presence of a significant number of high-luminosity H II regions (log L>39 dex). We also constructed the size distribution function, verifying that, as for most galaxies, NGC 1232 follows an exponential law. We also used the H{alpha} luminosity to calculate the star formation rate. An extremely interesting fact about this galaxy is that X-ray diffuse observations suggest that NGC 1232 recently suffered a collision with a dwarf galaxy. We found an absence of star formation around the region where the X-ray emission is more intense, which we interpret as a star formation quenching due to the collision. Along with that, we found an excess of star-forming regions in the northeast part of the galaxy, where the X-ray emission is less intense.
104. Star-forming regions in NGC 6822 from UV data
ID:
ivo://CDS.VizieR/J/ApJ/730/88
Title:
Star-forming regions in NGC 6822 from UV data
Short Name:
J/ApJ/730/88
Date:
21 Oct 2021
Publisher:
CDS
Description:
We characterize the star formation in the low-metallicity galaxy NGC 6822 over the past few hundred million years, using GALEX far-UV (FUV, 1344-1786{AA}) and near-UV (NUV, 1771-2831{AA}) imaging, and ground-based H{alpha} imaging. From the GALEX FUV image, we define 77 star-forming (SF) regions with area >860pc^2^, and surface brightness <~26.8 mag (AB) arcsec^-2^, within 0.2{deg} (1.7kpc) of the center of the galaxy. We estimate the extinction by interstellar dust in each SF region from resolved photometry of the hot stars it contains: E(B-V) ranges from the minimum foreground value of 0.22mag up to 0.66+/-0.21mag. The integrated FUV and NUV photometry, compared with stellar population models, yields ages of the SF complexes up to a few hundred Myr, and masses from 2x10^2^M_{sun}_ to 1.5x10^6^M_{sun}_. The derived ages and masses strongly depend on the assumed type of interstellar selective extinction, which we find to vary across the galaxy. The total mass of the FUV-defined SF regions translates into an average star formation rate (SFR) of 1.4x10^-2^M_{sun}_/yr over the past 100Myr, and SFR=1.0x10^-2^M_{sun}_/yr in the most recent 10Myr. The latter is in agreement with the value that we derive from the H{alpha} luminosity, SFR=0.008M_{sun}_/yr. The SFR in the most recent epoch becomes higher if we add the SFR=0.02M_{sun}_/yr inferred from far-IR measurements, which trace star formation still embedded in dust (age <~ a few Myr).
105. Surface photometry of BCD galaxies
ID:
ivo://CDS.VizieR/J/ApJS/156/345
Title:
Surface photometry of BCD galaxies
Short Name:
J/ApJS/156/345
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results from an analysis of surface photometry of B, R, and H{alpha} images of a total of 114 nearby galaxies (v_helio_<4000km/s) drawn from the Palomar/Las Campanas Imaging Atlas of blue compact dwarf (BCD) galaxies. Surface brightness and color profiles for the complete sample have been obtained. We determine the exponential and Sersic profiles that best fit the surface brightness distribution of the underlying stellar population detected in these galaxies. We also compute the (B-R) color and total absolute magnitude of the underlying stellar population and compared them to the integrated properties of the galaxies in the sample.
106. The Kepler-INT survey
ID:
ivo://CDS.VizieR/J/AJ/144/24
Title:
The Kepler-INT survey
Short Name:
J/AJ/144/24
Date:
21 Oct 2021
Publisher:
CDS
Description:
This paper describes the first data release of the Kepler-INT Survey (KIS) that covers a 116deg^2^ region of the Cygnus and Lyra constellations. The Kepler field is the target of the most intensive search for transiting planets to date. Despite the fact that the Kepler mission provides superior time-series photometry, with an enormous impact on all areas of stellar variability, its field lacks optical photometry complete to the confusion limit of the Kepler instrument necessary for selecting various classes of targets. For this reason, we follow the observing strategy and data reduction method used in the IPHAS and UVEX galactic plane surveys in order to produce a deep optical survey of the Kepler field. This initial release concerns data taken between 2011 May and August, using the Isaac Newton Telescope on the island of La Palma. Four broadband filters were used, U, g, r, i, as well as one narrowband one, H{alpha}, reaching down to a 10{sigma} limit of ~20th mag in the Vega system. Observations covering ~5 deg^2^, thus about half of the field, passed our quality control thresholds and constitute this first data release. We derive a global photometric calibration by placing the KIS magnitudes as close as possible to the Kepler Input Catalog (KIC) photometry. The initial data release catalog containing around 6 million sources from all the good photometric fields is available for download from the KIS Web site (www.astro.warwick.ac.uk/research/kis/) as well as via MAST (KIS magnitudes can be retrieved using the MAST enhanced target search page http://archive.stsci.edu/kepler/kepler_fov/search.php and also via Casjobs at MAST Web site http://mastweb.stsci.edu/kplrcasjobs/).
107. The SOS project. IV. NGC 1624 and NGC 1931
ID:
ivo://CDS.VizieR/J/AJ/149/127
Title:
The SOS project. IV. NGC 1624 and NGC 1931
Short Name:
J/AJ/149/127
Date:
21 Oct 2021
Publisher:
CDS
Description:
Young open clusters located in the outer Galaxy provide us with an opportunity to study star formation activity in a different environment from the solar neighborhood. We present a UBVI and H{alpha} photometric study of the young open clusters NGC 1624 and NGC 1931 that are situated toward the Galactic anticenter. Various photometric diagrams are used to select the members of the clusters and to determine the fundamental parameters. NGC 1624 and NGC 1931 are, on average, reddened by <E(B-V)>=0.92+/-0.05 and 0.74+/-0.17mag, respectively. The properties of the reddening toward NGC 1931 indicate an abnormal reddening law (R_V,cl_=5.2+/-0.3). Using the zero-age main sequence fitting method we confirm that NGC 1624 is 6.0+/-0.6kpc away from the Sun, whereas NGC 1931 is at a distance of 2.3+/-0.2kpc. The results from isochrone fitting in the Hertzsprung-Russell diagram indicate the ages of NGC 1624 and NGC 1931 to be less than 4 and 1.5-2.0Myr, respectively. We derived the initial mass function (IMF) of the clusters. The slope of the IMF ({Gamma}_NGC1624_=-2.0+/-0.2 and {Gamma}_NGC1931_=-2.0+/-0.1) appears to be steeper than that of the Salpeter/Kroupa IMF. We discuss the implication of the derived IMF based on simple Monte-Carlo simulations and conclude that the property of star formation in the clusters does not seem to be significantly different from that in the solar neighborhood.
108. The VVV Variables (V^4^) catalog
ID:
ivo://CDS.VizieR/J/ApJ/864/11
Title:
The VVV Variables (V^4^) catalog
Short Name:
J/ApJ/864/11
Date:
21 Oct 2021
Publisher:
CDS
Description:
Time-varying phenomena are one of the most substantial sources of astrophysical information, and their study has led to many fundamental discoveries in modern astronomy. We have developed an automated tool to search for and analyze variable sources in the near-infrared Ks band using the data from the VISTA Variables in the Via Lactea (VVV) ESO Public Large Survey. This process relies on the characterization of variable sources using different variability indices calculated from time series generated with point-spread function (PSF) photometry of sources under analysis. In particular, we used two main indices, the total amplitude {Delta}Ks and the eta index {eta}, to identify variable sources. Once the variable objects are identified, periods are determined with generalized Lomb-Scargle periodograms and the information potential metric. Variability classes are assigned according to a compromise between comparisons with VVV templates and the period of the variability. The automated tool is applied on VVV tiles d001 and d002 and led to the discovery of 200 variable sources. We detected 70 irregular variable sources and 130 periodic ones. In addition, nine open-cluster candidates projected in the region are analyzed, and the infrared variable candidates found around these clusters are further scrutinized by cross-matching their locations against emission star candidates from VPHAS+ survey H{alpha} color cuts.
109. Type Ibc SNe in disturbed galaxies
ID:
ivo://CDS.VizieR/J/ApJ/717/342
Title:
Type Ibc SNe in disturbed galaxies
Short Name:
J/ApJ/717/342
Date:
21 Oct 2021
Publisher:
CDS
Description:
We compare the radial locations of 178 core-collapse supernovae (CCSNe) to the R-band and H{alpha} light distributions of their host galaxies. When the galaxies are split into "disturbed" and "undisturbed" categories, a striking difference emerges. The disturbed galaxies have a central excess of CCSNe and this excess is almost completely dominated by supernovae of types Ib, Ic, and Ib/c, whereas type II supernovae dominate in all other environments. The difference cannot easily be explained by metallicity or extinction effects, and thus we propose that this is direct evidence for a stellar initial mass function that is strongly weighted toward high-mass stars, specifically in the central regions of disturbed galaxies.
110. UBVI and H{alpha} CCD photometry of NGC 6231
ID:
ivo://CDS.VizieR/J/AJ/145/37
Title:
UBVI and H{alpha} CCD photometry of NGC 6231
Short Name:
J/AJ/145/37
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have performed new wide-field photometry of the young open cluster NGC6231 to study the shape of the initial mass function (IMF) and mass segregation. We also investigated the reddening law toward NGC6231 from optical to mid-infrared color excess ratios, and found that the total-to-selective extinction ratio is R_V_=3.2, which is very close to the normal value. But many early-type stars in the cluster center show large color excess ratios. We derived the surface density profiles of four member groups, and found that they reach the surface density of field stars at about 10', regardless of stellar mass. The IMF of NGC6231 is derived for the mass range 0.8-45M_{sun}_. The slope of the IMF of NGC6231 ({Gamma}=-1.1+/-0.1) is slightly shallower than the canonical value, but the difference is marginal. In addition, the mass function varies systematically, and is a strong function of radius-it is very shallow at the center, and very steep at the outer ring suggesting the cluster is mass segregated. We confirm the mass segregation for the massive stars (m>~8 M_{sun}_) by a minimum spanning tree analysis. Using a Monte Carlo method, we estimate the total mass of NGC6231 to be about 2.6(+/-0.6)*10^3^M_{sun}_. We constrain the age of NGC 6231 by comparison with evolutionary isochrones. The age of the low-mass stars ranges from 1 to 7Myr with a slight peak at 3Myr. However, the age of the high-mass stars depends on the adopted models and is 3.5+/-0.5Myr from the non-rotating or moderately rotating models of Brott et al. (2011, cat. J/A+A/530/A115) as well as the non-rotating models of Ekstrom et al. (2012, cat. J/A+A/537/A146). But the age is 4.0-7.0Myr if the rotating models of Ekstrom et al. (2012, cat. J/A+A/537/A146) are adopted. This latter age is in excellent agreement with the timescale of ejection of the high-mass runaway star HD153919 from NGC6231, albeit the younger age cannot be entirely excluded.

Limit your search

more »

  • 2126