J/AJ/149/103 Spectroscopy of candidate YSOs in Serpens (Erickson+, 2015)
An optical spectroscopic survey of the Serpens main cluster: evidence for two
populations?
Erickson K.L., Wilking B.A., Meyer M.R., Kim J.S., Sherry W., Freeman M.
<Astron. J., 149, 103 (2015)>
=2015AJ....149..103E 2015AJ....149..103E
ADC_Keywords: Molecular clouds ; YSOs ; Photometry, UBVRI ; Spectral types ;
Rotational velocities ; Extinction ; Equivalent widths ;
Stars, masses ; Stars, ages
Keywords: ISM: individual: Serpens cloud - stars: formation -
open clusters and associations: general - stars: pre-main sequence
Abstract:
We have completed an optical spectroscopic survey of a sample of
candidate young stars in the Serpens Main star-forming region selected
from deep B, V, and R band images. While infrared, X-ray, and optical
surveys of the cloud have identified many young stellar objects
(YSOs), these surveys have been biased toward particular stages of
pre-main sequence evolution. We have obtained over 700 moderate
resolution optical spectra that, when combined with published data,
have led to the identification of 63 association members based on the
presence of Hα in emission, lithium absorption, X-ray emission,
a mid-infrared excess, and/or reflection nebulosity. Twelve YSOs are
identified based on the presence of lithium absorption alone. An
additional 16 objects are classified as possible association members
and their pre-main sequence nature is in need of confirmation.
Spectral types along with V and R band photometry were used to derive
effective temperatures and bolometric luminosities for association
members to compare with theoretical tracks and isochrones for pre-main
sequence stars. An average age of 2Myr is derived for this population.
When compared to simulations, there is no obvious evidence for an age
spread when considering the major sources of uncertainties in the
derived luminosities. However when compared to the young cluster in
Ophiuchus, the association members in Serpens appear to have a larger
spread in luminosities and hence ages which could be intrinsic to the
region or the result of a foreground population of YSOs associated
with the Aquila Rift. Modeling of the spectral energy distributions
from optical through mid-infrared wavelengths has revealed three new
transition disk objects, making a total of six in the cluster. Echelle
spectra for a subset of these sources enabled estimates of vsini for
seven association members. Analysis of gravity-sensitive lines in the
echelle and moderate resolution spectra of the association members
indicate surface gravities consistent with dwarf or sub-giant stars.
Description:
Over 700 moderate resolution spectra were obtained for 345 stars
selected from a (V-R) versus V color-magnitude diagram (Figure 1 in
the paper) as candidate Young Stellar Objects (YSOs).
B, V, and R band images were obtained on 2007 May 25 through light
cirrus with the 90prime wide-field camera on the 2.3m Bok Telescope.
Using one of the four CCDs (selected to give the highest quality for
photometry), the images covered a 30.7'*30.7' area with a scale of
0.45''/pixel centered on the Serpens Main cluster,
R.A.(2000)=18h29m56.7s, decl.(2000)=+01°12'24''.
Optical spectra were obtained using several instruments; Hydra,
Hectospec, a Boller and Chivens (B&C) spectrograph, and the Magellan
Inamori Kyocera Echelle (MIKE) spectrograph, on the WIYN, MMT, Bok,
and Magellan Clay telescopes, respectively. Observing parameters are
detailed as below:
----------------------------------------------------------------------------
Start date Telescope Spectrograph λ range Resolution
(in Å) (in Å)
(a)
----------------------------------------------------------------------------
2006 Jun 16 WIYN 3.5m Hydra 6249-7657 1.4
2008 Jun 28 Bok 2.3m B&C 5954-7115 1.2
2008 Sep 16 Bok 2.3m B&C 3850-5566 2.3
2009 Jun 27 WIYN 3.5m Hydra 3966-5386 1.4
... ... ... 6300-7669 1.4
2010 Jun 29 WIYN 3.5m Hydra 3900-5315 1.4
... ... ... 6286-7662 1.4
2010 Jul 03 MMT 6.5m Hectospec 5462-8070 1.2
2011 Sep 19 MMT 6.5m Hectospec 3703-9146 2.4
2009 Jun 13 Magellan Clay MIKE 3360-4991 0.11
6.5m
... ... ... 4830-8928 0.24
2009 Aug 10 Magellan Clay MIKE 3360-4991 0.11
6.5m
... ... ... 4830-8928 0.24
2010 Jul 09 Magellan Clay MIKE 3360-4991 0.11
6.5m
... ... ... 4830-8928 0.24
----------------------------------------------------------------------------
Note (a): Spectral resolution at central wavelength.
----------------------------------------------------------------------------
Table 2 presents the results using the moderate resolution spectra
from the B&C, Hydra, and Hectospec spectrographs. Table 3 presents the
results from the echelle spectra obtained with MIKE spectrograph.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 160 342 Optical properties of candidate Young Stellar
Objects (YSOs) with moderate resolution spectra
table3.dat 108 20 Optical properties of candidate Young Stellar
Objects (YSOs) with echelle spectra
table4.dat 133 63 Association members
table5.dat 86 16 Weak criteria sources
--------------------------------------------------------------------------------
See also:
J/ApJ/691/672 : Spectrocopy of YSOs in Serpens molecular cloud (Oliveira+ 2009)
J/ApJ/669/493 : Spitzer/Chandra YSOs in Serpens cloud core (Winston+, 2007)
J/A+A/463/275 : Chandra obs. of Serpens star-forming region (Giardino+, 2007)
J/A+A/421/623 : ISOCAM survey of YSOs in Serpens Cloud Core (Kaas+, 2004)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 21 A21 --- Type "Candidate YSOs" or "Photometric standards" type
23- 27 A5 --- r_Name Reference for Name (G1)
29- 38 A10 --- Name Stellar identifier
40- 42 A3 --- r_OName Reference for OName (G1)
44- 50 A7 --- OName Other stellar name
52- 66 A15 --- Obs Observational year and telescope used (1)
68- 69 I2 h RAh Hour of Right Ascension (J2000)
71- 72 I2 min RAm Minute of Right Ascension (J2000)
74- 77 F4.1 s RAs Second of Right Ascension (J2000)
78 A1 --- DE- Declination sign
79- 80 I2 deg DEd Degree of Declination (J2000)
82- 83 I2 arcmin DEm Arcminute of Declination (J2000)
85- 88 F4.1 arcsec DEs Arcsecond of Declination (J2000)
90- 98 A9 --- SpR Spectral type range
100-106 A7 --- SpT Adopted spectral type
108 A1 --- f_SpT [g] Indicates a spectral type from Winston et
al. (2009AJ....137.4777W 2009AJ....137.4777W) or Oliveira et al.
2009 (J/ApJ/691/672)
110-113 A4 --- Li? Is LiI emission present? (yes/no/poss=possibly)
115-118 A4 --- f_Li? [<1.6] Limit on column "Li?"
120 A1 --- l_EWHa [<] Upper limit flag on EWHa
121-127 F7.2 0.1nm EWHa [-110/14]? Hα equivalent width (in Å)
129-133 F5.1 0.1nm EWmax [-56/-1.2]? Maximum value of equivalent width (2)
135-139 F5.2 mag Vmag [8.43/20.72]? The V band magnitude
141 A1 --- f_Vmag [hf] V not observed, or blend (3)
143-146 F4.2 mag B-V ? The (B-V) color index
148-152 F5.3 mag V-R ? The (V-R) color index
154 A1 --- f_V-R [h] (V-R) not observed (3)
156-160 A5 --- o_Obs Number and region of observation code (4)
--------------------------------------------------------------------------------
Note (1): Years and telescopes used for observation are defined as follows:
06W = In 2006 with WIYN 3.5m telescope and Hydra spectrograph;
08B = In 2008 with Bok 2.3m telescope and Boller and Chivens (B&C)
spectrograph;
09W = In 2009 with WIYN 3.5m telescope and Hydra spectrograph;
10M = In 2010 with MMT 6.5m telescope and Hectospec spectrograph;
10W = In 2010 with WIYN 3.5m telescope and Hydra spectrograph;
11M = In 2011 with MMT 6.5m telescope and Hectospec spectrograph.
Note (2): When a value is present, its associated equivalent width (EW) value in
the previous column (EWHa) is the minimum value observed.
Note (3): The two flags on Vmag are defined as follows:
h = V and R band data were not available for 5 sources. They were dereddened
using 2MASS photometry: Jmag replaces Vmag and (J-H) replaces (V-R).
f = Source has a known companion, not resolved in our photometry.
Note (4): Spectral region observed and number of observations in each wavelength
range (see the "Description" section above for exact wavelength range for
each telescope/set of observations) are defined as follows:
1B = One observation in blue spectral region;
1R = One observation in red spectral region;
2B = Two observations in blue spectral region;
2R = Two observations in red spectral region;
3B = Three observations in blue spectral region;
3R = Three observations in red spectral region;
4R = Four observations in red spectral region.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- r_Name Reference for Name (G1)
7- 16 A10 --- Name Object name (1)
18- 20 A3 --- r_OName Reference for OName (G1)
22- 32 A11 --- OName Other name
34- 35 I2 h RAh ? Hour of Right Ascension (J2000)
37- 38 I2 min RAm ? Minute of Right Ascension (J2000)
40- 43 F4.1 s RAs ? Second of Right Ascension (J2000)
44 A1 --- DE- Declination sign
45- 46 I2 deg DEd ? Degree of Declination (J2000)
48- 49 I2 arcmin DEm ? Arcminute of Declination (J2000)
51- 54 F4.1 arcsec DEs ? Arcsecond of Declination (J2000)
56- 66 A11 "Y:M:D" Date Date of observation
68- 72 A5 --- SpR Spectral type range
74- 77 A4 --- SpT Spectral type (2)
79- 83 A5 --- LC Luminosity class (range of surface gravity)
85- 87 I3 km/s vsini0 [14/140]? Rotational velocity (or starting
rotational velocity range for SCB 40 and
SCB 70) (3)
89- 90 I2 km/s e_vsini0 ? Standard deviation of the mean in vsini0
92- 93 I2 km/s vsini1 [24/25]? Ending rotational velocity range for
SCB 40 and SCB 70 (3)
95 I1 km/s e_vsini1 ? Standard deviation of the mean in vsini1
97 A1 --- f_YSO Indicates that Hα emission is variable
and not detected in the echelle spectrum
99-108 A10 --- YSO YSO criterion (G2)
--------------------------------------------------------------------------------
Note (1): This table presents the results from the echelle spectra obtained with
Magellan Clay 6.5m telescope and MIKE spectrograph.
Note (2): Spectral types derived from Magellan spectra only; See Table 4 for
adopted spectral type.
Note (3): In most cases, the value of vsini was not sensitive to surface gravity
and is represented by a single value. A range is given only for SCB 40 and
SCB 70. When the surface gravity was indeterminate, a dwarf surface gravity
was assumed.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- r_Name Reference for Name (G1)
7- 16 A10 --- Name Object name
18- 20 A3 --- r_OName Reference for OName (G1)
22- 32 A11 --- OName Other name
34- 35 I2 h RAh Hour of Right Ascension (J2000)
37- 38 I2 min RAm Minute of Right Ascension (J2000)
40- 43 F4.1 s RAs Second of Right Ascension (J2000)
44 A1 --- DE- Declination sign
45- 46 I2 deg DEd Degree of Declination (J2000)
48- 49 I2 arcmin DEm Arcminute of Declination (J2000)
51- 54 F4.1 arcsec DEs Arcsecond of Declination (J2000)
56- 59 A4 --- SpT Spectral type
61 A1 --- f_SpT [d] Indicates a spectral type from Winston
et al. (2009AJ....137.4777W 2009AJ....137.4777W) and Oliveira
et al. 2009 (cat. J/ApJ/691/672)
63 A1 --- l_Av [>] Lower limit flag on Av
64- 68 F5.2 mag Av [0/22]? Extinction
69 A1 --- f_Av [e] Indicates that 2MASS (J-H) photometry
is used to compute Av and JMag
71 A1 --- l_VMag [<] Upper limit flag on VMag
72- 76 F5.2 --- VMag [-1.21/12]? Absolute V-band magnitude
78 A1 --- f_VMag [e] JMag recorded (situation where J and H
were used to deredden in Table 2)
80 A1 --- l_logL [>] Lower limit flag on logL
81- 85 F5.2 [Lsun] logL [-1.7/3]? Log of the bolometric luminosity
87- 90 F4.2 [Lsun] e_logL ? 1σ uncertainty on logL
92 A1 --- l_logT [>] Lower limit flag on logT
93- 96 F4.2 [K] logT [3.48/4.18]? Log of the effective temperature
98-101 F4.2 [K] E_logT ? Upper 1σ error in logT
103-106 F4.2 [K] e_logT ? Lower 1σ error in logT
108-111 F4.2 Msun Mass [0.14/5.1]? Mass (1)
113 A1 --- l_logA [<] Upper limit flag on logA
114-117 F4.2 [yr] logA [5/8]? Log of the age (1)
119-133 A15 --- Mm Association membership criterion (G2)
--------------------------------------------------------------------------------
Note (1): Masses and ages estimated from the tracks and isochrones of D'Antona &
Mazzitelli (1997MmSAI..68..807D 1997MmSAI..68..807D) and F. D'Antona & I. Mazzitelli (1998,
private communication) except for the two B stars for which the Siess et
al. (2000A&A...358..593S 2000A&A...358..593S) models were used.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Name ? Object name from infrared ISO survey by
Kaas et al. 2004 (cat. J/A+A/421/623)
8- 9 I2 h RAh Hour of Right Ascension (J2000)
11- 12 I2 min RAm Minute of Right Ascension (J2000)
14- 17 F4.1 s RAs Second of Right Ascension (J2000)
18 A1 --- DE- Declination sign
19- 20 I2 deg DEd Degree of Declination (J2000)
22- 23 I2 arcmin DEm Arcminute of Declination (J2000)
25- 28 F4.1 arcsec DEs Arcsecond of Declination (J2000)
30- 31 A2 --- SpT Spectral type
33- 35 F3.1 mag Av [3.8/7.9] Extinction
37- 40 F4.2 mag VMag [1.37/6.79] Absolute V-band magnitude
42- 46 F5.2 [Lsun] logL [-0.56/1.36] Log of the bolometric luminosity
48- 51 F4.2 [Lsun] e_logL 1σ uncertainty in logL
53- 56 F4.2 [K] logT [3.62/3.86] Log of the effective temperature
58- 61 F4.2 [K] E_logT Upper 1σ error in logT
63- 66 F4.2 [K] e_logT Lower 1σ error in logT
68- 70 F3.1 Msun Mass [0.6/2.3] Mass (1)
72- 75 F4.2 [yr] logA [5.61/7.3] Log of the age (1)
77- 86 A10 --- Weak Weak criteria source (2)
--------------------------------------------------------------------------------
Note (1): Masses and ages estimated from the tracks and isochrones of D'Antona
& Mazzitelli (1997MmSAI..68..807D 1997MmSAI..68..807D) and F. D'Antona & I. Mazzitelli (1998,
private communication).
Note (2): Weak criteria sources sit above the main sequence with the following
properties:
ext = An AV>3.5mag;
possLi = Possible lithium absorption;
weakHa = The presence of weak Hα emission (10Å>EW(Hα)>5Å).
--------------------------------------------------------------------------------
Global Notes:
Note (G1): Source names from X-ray, optical or infrared studies defined as
follows:
SCB = Straizys et al. (1996BaltA...5..125S 1996BaltA...5..125S);
XMM = XMM-Newton survey by Preibisch (2003A&A...410..951P 2003A&A...410..951P);
WMW = Spitzer survey by Winston et al. 2007 (cat. J/ApJ/669/493);
CDF88 = Reflection nebulae survey by Chavarria-K. et al. (1988A&A...197..151C 1988A&A...197..151C);
KOB = ISO survey by Kaas et al. 2004 (cat. J/A+A/421/623);
GFM = Chandra survey by Giardino et al. 2007 (cat. J/A+A/463/275);
EC = Eiroa & Casali (1992A&A...262..468E 1992A&A...262..468E);
SVS = Strom, Vrba, & Strom (1976AJ.....81..638S 1976AJ.....81..638S);
2MASS = 2Micron All-Sky Survey (cat. II/246).
Note (G2): The criteria are defined as follows:
IRX = An infrared excess;
TD = Identification as a possible Transition Disk object;
X = X-ray emission;
RefNeb = Association with reflection nebulosity;
Ha = The presence of Hα emission with equivalent width (EW) >10Å;
Li = Lithium absorption;
ext = Location above the main sequence and AV>3.5mag.
History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 13-Apr-2015